Presentation on theme: "Conservation Biology (Biol 4350/5350) Fall 2012 Chapter 1: What is Conservation Biology? (A fairly brief overview)"— Presentation transcript:
Conservation Biology (Biol 4350/5350) Fall 2012 Chapter 1: What is Conservation Biology? (A fairly brief overview)
Almost all ecosystems on Earth have been impacted by humans to some extent; rate and degree is increasing exponentially with growth of the human population (about 6 billion people currently). Climate change, pollution, biogeochemical cycles, extinctions, habitat destruction and change, loss or alteration of genetic variation... Affects humans directly and indirectly.
1.1 Estimated global human population size from the last Ice Age to the present
1.2 United Nations projections for human population growth to 2050
1.3 Number of global hectares per person needed to support current lifestyles
BUT: Human growth rate has slowed in many countries. Much depends on how people act and how much they consume, not just how many there are -- and consumption is much lower in 3rd World countries; this can change in developed countries too.
And: Highest birth rates are in places where many family members are needed to achieve success at low-skill tasks. Education and targeted economic development can reduce the incentive to produce large families.
Try to achieve a balance between human needs and maintenance of biodiversity through sustainable development. Conservation biology: Many ideas are old, but really became a science in the 1980s: ties together areas of biology such as wildlife and habitat management, to population genetics, to evolution, to ecological modeling etc. Integrates with chemistry, geology, anthropology, sociology, economics...
Elements unique to the “new” conservation biology: 1)Spans the previous gap between pure and applied research; management plans consider genetic, theoretical, and many other kinds of data (not just counting trees, deer, etc.). Now, conservation biology is firmly established as rooted in real academic research.
2) Earlier approaches were largely human- oriented (anthropocentric) and utilitarian: focused on maintaining species that people use or like (timber, fisheries, flashy species etc.), and “useful” components of ecosystems (e.g., water). Now much more concern about diversity of a wide range of species (which may in turn help preserve the ones that are directly useful to humans).
And -- growing recognition that biodiversity itself has inherent value; healthy ecosystems are the “support system” of the planet. (Also, wider view of “intrinsic value” -- biodiversity is valuable regardless of its direct benefits to humans -- we’ll discuss this more later).
3) Realization of the importance of integrating conservation strategies with work of non-scientists: economics, politics, social sciences, urban planning, etc. People have to cooperate, establish viable alternatives, and understand the benefits of preserving biodiversity.
In the broadest sense, conservation biology tries not only to maintain diverse species, but also genetic diversity and genetic “integrity”: protect populations and gene flow. And, keep entire ecosystems functioning normally while recognizing that change (ecological, evolutionary) does occur even without human intervention.
Conservation biology, from a scientific perspective, is an attempt to maintain normal evolutionary processes within normally functioning ecological settings.
Even in ancient Greece (for example), massive habitat destruction was in progress, and was recognized. Huge areas of S. Europe, Mediterranean, and SW Asia were once called “the land of perpetual shade”; forests were destroyed to build ships etc.; now barren and/or desert.
The degree of human impact has depended partly on population density and partly how long people stayed in one place. Small groups of hunter-gatherers often have low impact; move on when local resources become scarce and resources can regenerate.
Some societies practiced sustainable agriculture, using selected areas, moving on, and allowing these areas to go through normal successional stages. But as agriculture became more sophisticated and permanent, ability of ecosystems to regenerate diminished. And -- demand for resources continues to grow.
Europe was essentially deforested by the 1700s, except for land held by the rich; many areas of China etc. similar. So, by the time there was a real interest in conservation, much of the natural habitat was lost. North America: Originally aboriginal peoples; probably low impact (except hunting of large mammals?).
Then: European colonization, exploitation of forests and other resources. And -- a lot of resources were sent back to Europe, where the demand was much greater; exploitation was no longer just local (and this continues to be a problem throughout the World).
Early approaches to conservation biology in the U.S.: Romantic-Transcendental Conservation Ethic: Rooted partly in the writings of Thoreau, Emerson, Muir. Philosophical view that nature is the work of God -- a “temple” -- not just for human/economic benefit. Today, this view is exemplified by groups such as the Sierra Club.
2) Resource Conservation Ethic: Formalized around the beginning of the 20th Century by Pinchot, following J.S. Mill and others. View of “useful” versus “non-useful” components of nature (an anthropocentric approach). Multi-use concept: get as much as possible out of an area (timber, fish, grazing, etc.); develop management strategies to achieve this.
Still seen with groups like the Forestry Service, fisheries management agencies, Ducks Unlimited etc. This established the “preservationist” versus “utilitarian” schools of thought. Then 3) Leopold’s Evolutionary-Ecological Land Ethic (EELE): mid-20th Century.
Still seen with groups like the Forestry Service, fisheries management agencies, Ducks Unlimited etc. This established the “preservationist” versus “utilitarian” schools of thought. Then 3) Leopold’s Evolutionary-Ecological Land Ethic (EELE): mid-20th Century.
EELE was rooted in the emerging science of evolutionary ecology. Can’t just break nature into “useful” and “non-useful” elements, and need to understand how it works. Study various components of ecosystems and their interactions to protect them as a whole in an informed way. Larger an “equilibrium” view (shifted more to non-equilibrium as knowledge grew).
The EELE provided the broadest and most useful approach, and much of the fundamental basis of modern conservation biology (although now, there’s much more emphasis on the human element as well).
1960s-1970s: Biologists started to wake up to the fact that entire ecosystems were disappearing; biodiversity was disappearing rapidly; also, pollution and other human-induced problems gained wide awareness. Conservation efforts at the time were largely utilitarian or focused on appealing species; need for an ecosystem approach became evident.
1980: Soulé and Wilcox published Conservation Biology: An Evolutionary Perspective Major turning point, followed by other works that emphasized evolutionary biology as much of the basis for conservation.
1985: Society for Conservation Biology (and their journal Conservation Biology) were established. Provided a venue for evolutionary and genetic approaches to conservation. The field continues to grow, integrating a wide range of areas of science (including new genomic tools) and study of human activities.
Our text: Three guiding principles that establish a paradigm (“world view”) for conservation biology. 1) Evolutionary change: A unifying theme throughout biology: explains origins and patterns of biodiversity; genetic change is central to evolution; don’t want to stop evolution -- instead, ensure that populations and species experience natural genetic change, including adaptation, in response to natural forces.
2) Dynamic ecology: Ecological systems are rarely at equilibrium, and if so don’t stay that way long -- no truly stable point. External forces -- floods, fires, invaders, etc. can “perturb” the system or change it drastically; ecosystems are usually patchy and shift over time.
This view is directly relevant to factors such as preserve design; e.g., habitat corridors to allow movement and gene flow, and consideration of temporal factors. And of course -- ecosystems are inherently dynamic because evolution of the organisms within them is happening all the time.
3) Human presence: Can’t leave humans out of the picture; we’re here to stay (?), and people won’t support conservation efforts if natural areas are simply barricaded off etc. Need to consider human needs, educate/build pride in local habitats, tie conservation to economic incentives, recognize rights of native groups -- and also, incorporate the knowledge that they have of the ecosystems and organisms.
Conservation biology is inherently interdisciplinary, and also inherently inexact in many ways: blending complex systems, human components, “hard” versus “soft” science, public policy etc. And, since ecology and evolution are not strictly predictable, there’s a strong component of probability, plus the need to consider many factors that could alter expected outcomes -- need to build in safety margins.
1.9 The interdisciplinary nature of conservation biology
1)Genetic diversity: Determines every level of biodiversity. Number of genes ranges from a few (viruses), to several hundred (many bacteria) to tens of thousands (e.g., humans: 20,000 +). Genetic variation is constantly arising (mutation, recombination): essential to evolution.
Levels of genetic variation are often considered indicators of the “health” of a population or species: may provide resilience to changing conditions. Also critical in captive breeding and management.
Understanding genetic diversity is essential to understanding gene flow, population structure, intra- and interspecific interactions, relationships to environment, species boundaries and evolutionary history...
Population level diversity: Describes, in part, nature and distribution of genetic variation within and among populations. e.g., local adaptations; species-wide variation (disease resistance, nutrient use, etc. And: genetically-determined phenotypic plasticity may be very important.
Prioritization of populations for conservation: maximize diversity? Different populations may play different roles in different ecosystems (may or may not be genetically determined). e.g., a pollinator, predator, etc. may be crucial in some systems: not always obvious until after it’s gone.
3) Human cultural diversity: Cultures evolve too, and interactions with environment vary tremendously (good and bad): many have a long history of managing/sustaining natural resources. How many human cultures are there? Over 6500 known languages (one indicator).
Can also measure by number of indigenous populations: generally highest in tropics (where biodiversity is usually highest too). So: complex human/environment interactions; these determine cultural adaptation. Often overlooked, especially in context of conservation strategies.
2.1 Linguistic diversity and numbers of indigenous cultures across the world (Part 1)
2.1 Linguistic diversity and numbers of indigenous cultures across the world (Part 2)
4) Species-level diversity: For now, just think of number of species in a given area (more correctly, this is species richness). Species are often viewed as the “fundamental” units of evolution (many would argue populations). But certainly they are the “biggest” (most inclusive) units of evolution.
Higher level taxa (genera, families...phyla, kingdoms, domains) do NOT evolve. These are collections of evolving species, designated by humans. Boundaries of higher-level taxa are largely arbitrary, although nearly everyone agrees that they should reflect evolutionary history and be monophyletic (= ancestor + all descendants).
2.2 (A) Domains of biodiversity: Bacteria, Archaea, and Eukarya
Much of conservation biology is species- focused: US Endangered Species Act (ESA); Convention on International Trade in Endangered Species (CITES); many others, often more localized. Danger: Can ignore what’s happening at the population level; lose genetic diversity in the wild and in preserves/captive populations.
What is a species? Many views; can be extremely important from a conservation, political, and legal perspective. Very important to distinguish between CONCEPT and PRACTICAL APPLICATION. Species recognition/designation is a hypothesis, and often testable.
“Classic” concept: Biological Species Concept (Dobzhansky, Mayr): “A species is a group of actually or potentially interbreeding populations which are reproductively isolated from other such groups”.
BUT: Problematic in many ways. Practical: Often very hard to test, especially with non-sympatric organisms. Fundamental: Lots of species interbreed to varying extents (and reproductive compatibility could just be a retained ancestral condition). What about asexual lineages?
Very restrictive: if two groups are sympatric (live in same area) and don’t ever interbreed -- yes, they are different species. Or if they interbreed and offspring are completely inviable or sterile -- different species. But what about the in-betweens? Say, slightly reduced fitness (or even higher fitness of hybrids).
Over 99.99% of all species on Earth are recognized based on indirect evidence of reproductive isolation: morphology, behavior, etc. (or simply no consideration of reproductive isolation).
Phylogenetic Species Concept: Not really “phylogenetic”; simply requires that a group be monophyletic, interbreeding, and display some feature unique to the group (an autapomorphy). But -- in practice, almost any population could be a species. And, do species have to be distinguishable at all? (Conceptually)
Evolutionary Species Concept (Simpson, Wiley and others): This is a real concept. A species is “a single lineage of ancestral-descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate”. (A lineage concept).
What are the implications? Maybe we’ll never be able to detect all species -- sometimes we have sufficient evidence, sometimes not. Unsatisfying to many (including lawyers!) who want some simple, quantifiable measure (say, genetic distance). But there isn’t one.
Are species real entities? Some would argue that they’re just human constructs, it’s all a continuum, etc. But obviously there are distinct lineages with distinct identities. If you don’t think that species are real, then you can make up various criteria -- but they will never hold up across different groups.
In legal situations, it’s common to invoke the Biological Species Concept -- which is rarely testable (so supposedly, if its requirements can’t be satisfied, then a given unit isn’t “proven” to be a distinct species).
And -- back to the issue of what to protect -- if the goal is genetic diversity, evolutionary potential, etc., then populations etc. may even be more important. The ESA does allow for protection of distinct “subspecies” and populations (Evolutionarily Significant Units, ESUs), but just for vertebrates, and generally less valued than full species.
And, if populations are the units of evolution, if there’s local adaptation, geographic genetic variation, if different populations play different roles in different ecosystems -- Then, protecting just one or a few select populations (or captive breeding) may provide a false sense of security.
Species-only focus can lead to loss of genetic diversity: consider crop plants: may have lost resistance to disease (or that ancestral population didn’t have it): If the wild ones are gone, usually irreversible.
Pros of species emphasis: Allows focus on particular entities, and a basis for estimating biodiversity. Can appeal to public (e.g., Giant Panda etc.) and at the same time protect whole ecosystems.
But -- Problematic if the approach obscures attention to ecosystems and results in only select species being protected in isolation of their ecological context. Captive breeding is an especially strong example.
Have to be careful, too, that species aren’t overlooked. Especially with molecular genetic advances (DNA sequencing etc.) many new species are being discovered that were “cryptic” (e.g., not identifiable based on morphology). So one “species” often is two, or even many (salamanders are a great example).
How many species on Earth? Described (= formally recognized): about 1.75 million living, plus about 300,000 fossils. Dozens to hundreds described every day; hundreds to thousands probably go extinct every day, before we even know that they exist.
Wide range of estimates: about 10 million - 100 million (text says high end is 50 million). Probably more. Fungi: About 80,000 described species; 1 million+ suspected. And viruses, bacteria, archaeans, etc. -- just beginning to scratch the surface (even though these may be critical to ecosystems worldwide).
e.g., fogging of tropical forest canopies reveals huge number of species previously unknown (55% new); think of the oceans! Even vertebrates: salamanders in central Texas: at least 12 species when there were only 4 recognized until recently; 4 new ones described in last few years, some right in the city of Austin and nearby urbanizing areas.
Table 2.1 in text: Bacteria: About 5,000 described species; around 1 million expected. Nematodes: About 25,000 described; around 400,000 expected. Arthropods: About 1 million+ described; around 9 million expected. Chordates: 58,000; 60,000
Diversity of higher-level taxa: classifications are controversial, but at least 3 Domains: Bacteria (= Eubacteria), Archaea, and Eukaryota; many biologists recognize 20+ Kingdoms (previously 5 at most) Preservation of higher-level taxa: even though these are human constructs, usually distinguished by “key innovations”; lose the whole group and lose a key part of biodiversity
2.2 (A) Domains of biodiversity: Bacteria, Archaea, and Eukarya
Consider genetic diversity using evolutionarily ancient small subunit ribosomal RNA gene: sequence diversity seen in animals, true plants, and fungi only about 10% of that seen across the rest of Life. Origins of many groups most familiar to us are relatively recent.
Deeper splits (e.g., among Domains) are billions of years old (Life arose at least 3.6 billion years ago, not long after Earth became habitable).
Biological communities: often hard to define: Species + interactions with each other and the environment. Changes across landscape with abiotic factors etc.
Species richness and species diversity: Richness = simple count of number of species (often a selected group). Includes both rare and abundant species. Diversity: Weighted measure of species “evenness”, based on numbers, biomass, productivity, etc.
e.g., if all species equally abundant, high degree of evenness. Various indices of similarity in diversity across ecosystems; provides an indication of habitat types (e.g., high proportion of one tree species may be predictive of the kind of ecosystem, versus similar abundances of many species).
Richness can be measured on different scales: “alpha richness” describes number of species in a given area. “Beta richness” describes change in species composition (cumulative number, or turnover -- i.e. change in species composition along a gradient). “Gamma richness”: Larger scale extension of beta richness.
Alteration of habitat, climate change, pollution, and other human-caused (anthropogenic) changes often lead to changes in both species richness and diversity. “Weedy”, resilient species take over: raccoons, blue jays, tough plants; often introduced species: less richness, more evenness (some species may persist, but their numbers become low).
BUT: Many biologists still focus on richness, partly because rare species may be very important (“keystone species” and “ecological engineers” for e.g.). These may be more vulnerable to being completely lost, and are often harder to census. Note: indices of richness and diversity rarely distinguish between native and introduced species.
Importance of particular species is often hard to assess, and understanding how a community or ecosystem works is extremely complex and difficult. This is a key reason why conservation biologists often focus on selected species (and often hope that this will preserve the whole ecosystem).
Richness/diversity of biomes and ecosystems worldwide: traditionally focused on plant composition (and later climatic factors too). Eight major terrestrial biogeographic regions are generally recognized:
1)Palearctic (northern part of Old World, from Europe and N. Africa through N. and N.-central Asia). 2) Afrotropic 3) Indo-Malay 4) Australasian
5) Oceania (S. Pacific islands) 6) Nearctic (Arctic through Caribbean and Mexico) 7) Neotropical (New World tropics) 8) Antarctic
Each has ecological gradients: consider temperate latitudes: can follow precipitation gradients. Wet forest to woodland to desert; boreal forest in north,then tundra: call these ecosystem types biomes. Tropics: Rainforest, evergreen seasonal forest, dry forest, thorn woodland, desert scrub, desert.
Elevational gradients: e.g., lowland rainforest, montane rainforest, cloud forest, elfin woodland, paramo (alpine tundra above treeline). Biomes can be further subdivided by slope, soil type, species present, etc. Of course, hard to define precisely.
2001: World Wildlife Fund recognized 867 terrestrial “ecoregions”: large areas with key communities, ecological characteristics, and usually some major groups of species spread through the region. More than 1000 researchers involved; the most comprehensive basis for classifying landscape-level richness/diversity on a broad scale.
Each ecoregion has a variety of habitat types; try to preserve as much of each in each ecoregion to maximize richness and biodiversity. Major attempts are underway to to classify marine ecoregions: their ecosystems are extremely important but still little understood.
Geological history of species richness: Determined by rate at which species arise vs. go extinct. Various factors may promote speciation; vicariance (geographic splitting) is arguably the most important. And -- the more species there are,
And -- the more species there are, the more (theoretically) chances there are for further speciation: feedback and exponential effects.
Loss (extinction) rates driven largely by disturbance (although some level of disturbance may promote speciation and species richness). Also competition, predation, disease, etc.
Life arose at least 3.6-3.8 BYA: prokaryotic, then eukaryotes too by about 2 BYA. Species richness probably low until around 1.6 BYA (late Precambrian -- but early organisms probably didn’t fossilize well). Mass extinctions: try to distinguish from “background” extinction rate.
Then, arthropod and echinoderm-like animals appear in the fossil record, plus other lineages that probably have gone extinct. Early Cambrian (approx. 550-600 MYA): “explosion” of speciation? Also, more organisms that fossilize better (e.g., shells). Another pulse starting about 450 MYA.
Five “major” extinction events often recognized (plus the sixth happening now). A big one: Permian extinction approx. 250 MYA: Pangaea breaking up, currents, climate changing, possibly asteroid impact: estimated 95% of species lost (note that next figure estimates loss of families).
Another big one: Cretaceous extinction at K/T (Cretaceous/Tertiary) boundary approx. 65 MYA. Asteroid impact; estimated 75% of species extinct, including most dinosaurs. On average, species richness seems to recover in 10+ MY. And, massive losses may open up opportunities for new species; overall, richness has increased.
Terrestrial vascular plants by about 400 MYA; major explosion of angiosperms starting approx. 150 MYA, then especially 65 MYA. Appears to be correlated with explosion in insects: maybe each promoted the other. Diversification of angiosperms may have fueled that of terrestrial animals (and other organisms).
Endemism: Localization of a species to a particular area (some bacteria are endemic to most of the Earth; other species may be endemic to just a tiny island). Largely the result of vicariance (geographic separation); also specialization for particular environmental conditions; a particular group may be endemic to an area if the ancestor gave rise to multiple species.
Islands have high levels of endemism, but not necessarily richness (depends partly on size of island). But: oceanic islands with coral reefs have high richness and endemism -- for example, western Pacific islands
Patterns of endemism greatly among taxa in a given area; species with high dispersal may be widespread, and intrinsic features of the organisms may promote localization, due to resource requirements or the nature of speciation
Cape of South Africa, southwestern Australia: low endemism of mammals and birds, extremely high endemism of plants. May be due to polyploidization: fairly rare in animals, common in angiosperms: promotes localized speciation. Marine systems: much less understood than terrestrial.
2.10 The Indo-West Pacific is a marine diversity hotspot
Latitudinal gradients in richness: For most groups, species richness highest closest to the equator -- true for terrestrial and marine organisms. Ants: Locally, around 10 species far north/south, up to 2000 in some areas of tropics; breeding birds: Greenland 56, NY 105, Colombia 1395; bivalves (see next figure).
Number of species, genera, and families of marine molluscs by latitude
Reason for latitudinal gradient still unclear; probably combination of factors: -speciation vs. extinction rates? -habitat heterogeneity? -energy availability (productivity)? -levels of gene flow?
In general, a major determinant of species richness is area: highly correlated with speciation and extinction rates. First noted by Arrhenius; true of both islands and whole continents.
Species - area curves: S = cA z Where S = number of species, A = area, c and z: constants fitted to area On log scale, linear: c = y-intercept and z is slope Next figures: Caribbean amphibians and reptiles; Pacific birds
Generally, z is about -0.15 for continents -biotic provinces within a continent: 0.19 -islands associated with continents range from about 0.25-0.45 (varies partly according to proximity to mainland = colonization, or islands that periodically connect to mainland)
MacArthur and Wilson (1960s): Theory of Island Biogeography: predict number of species based on island size, proximity to mainland, colonization vs. extinction rates.
Consider areas of climatic similarity: largest in tropics: -little change in temperature at middle latitudes -middle latitude bands have higher surface area - larger area: higher speciation rates, lower extinction = high richness
Perhaps more stability in tropics; also generation time effects/frequency of reproduction. More generations = more genetic variation = faster evolution = more speciation?
Energy effects: the more energy from the sun, the more biomass per unit area can be generated; higher packing of individuals (and probably species). High energy input (especially with high moisture) may put less strain on individuals, allow more of their energy for reproduction; may even allow greater dietary specialization, contributing to speciation.
Feedback effects: more species, more speciation. Primary productivity: primary source of energy available to organisms; a function of temperature, moisture, nutrients.
2.14 Numbers of species of Eucalyptus and Acacia in southwestern Australia
2.15 Plant species richness in Borneo (1-3) and in southwestern Australia (4-5)
Number of species of marine molluscs, by salinity
Effects of disturbance on species richness: Major, cyclical disturbance: climate change (except that now it’s probably permanent): especially strong in N and S latitudes. If it happens fast, species can’t adapt; life history disrupted, ranges shift, extinction rate increases.
Magnitude and and localization of disturbance is important: Small: storms, floods, disease, competition, predation etc.: generally localized; if extreme, richness may suffer but can probably recover. Widespread and major: maybe not, at least in the short term.
Some argue that stability of habitat allows species to accumulate (e.g., deep ocean floors): productivity low, but patches of resource-richness (e.g., hydrothermal vents). So -- promotes genetic isolation, speciation; little disturbance to cause extinction. Maybe the same for the tropics (perhaps a long history of stability?).
Interactions among organisms: competition may reduce alpha richness if one or a few species take over. BUT: Can also promote richness if it encourages niche partitioning. Depends on resources and population densities.
Predation: Classic example: sea stars on Pacific coast. Eat mussels that otherwise would dominate the community. Sea stars present in low numbers, but keep competition in check (remove sea stars and richness decreases. Similar: grazing of prairie plants by buffalo may promote richness.
Intermediate Disturbance Hypothesis: Disturbance by changes in abiotic or biotic environment (especially from outside sources), at medium levels, prevents takeover by a few species. Also increases diversity in the sense of promoting evenness.
More extreme disturbance: Knocks back richness (eliminates some species, directly or indirectly causes increased competition etc.). And, frequent disturbance may prevent individuals from maximizing reproductive potential. So intensity and frequency of disturbance contribute to richness (and diversity) (“optimum” varies by ecosystem).
Local and regional species richness: Ecological communities are shaped by local species interactions and environment, but broader-scale processes are critical on time and spatial scales. Local: mutualism, competition, predation; large scale: biogeographic history, phylogeny, dispersal, speciation...
Is there a limit to species richness? Maybe, for a given community: interactions plus abiotic environment may be constraints. May be a limit to how specialized a given species can be re: resources; limit to levels of niche overlap. Many other factors can be limiting: pollination, parasitism, predation, etc.
Many groups show pattern of increasing alpha (local) richness with increasing regional (beta) richness, but rate of local richness increases more slowly. For many systems, local interspecific interactions may be most important in determining alpha richness, and relative abundances of species (and thus, measures of diversity).
Importance of “biodiversity”: value to humans is a practical consideration. e.g., number of species of wild bees directly determines crop pollination efficiency: preserve nearby habitat; nutrient cycling key to human activities; medical compounds, etc.
Chapter 3: Threats to Biodiversity Humans are the biggest direct and indirect threat to biodiversity (besides occasional asteroid impacts etc.).
3.1 Major forces that threaten biological diversity
Major categories of anthropogenic effects: 1)Habitat degradation: Pollution, change of native habitat, introduced species, fragmentation, complete destruction.
3.6 Habitat loss and degradation is the greatest threat to global biodiversity among these groups
Major categories of anthropogenic effects cont’d: 2) Overexploitation: Logging, fishing, medicines, pet trade: may eliminate species or reduce numbers to the point of genetic inviability.
3) Introduced species: Sometimes a component of 1). e.g., introduced plant takes over and changes habitat. Also competition, predation (e.g., brown tree sanke in Guam has wiped out some native birds); disease; changes in interactions among native species.
4) Human-induced climate change: Previous mass extinctions often tied to major climate change -- continental drift, impact of extraterrestrial objects. Climate is now changing fast, and change is accelerating: population growth, industrialization.
Feedback effects: e.g., Arctic ice melts, exposes soil, absorbs more heat, more decomposition, releases CO 2... Cumulative/synergistic effects of changes: one pollutant may not be a big problem, but can increase vulnerability to disease, parasites, other pollutants. And: bioaccumulation of toxins in food chain/web.
3.2 Toxic chemicals that accumulate in fatty tissues concentrate at the top of the food chain
Essay 3.1 (A) Transient killer whales represent the most PCB-contaminated marine mammal (white = male, gray = female). Transients eat marine mammals; residents eat fish; females pass PCBs to offspring via milk.
Corals: symbiotic photosynthetic “algae”: warm water and/or pollutants cause symbiont to leave. Coral bleaching; corals die, and so does the whole reef ecosystem.
Cascade (snowball) effects: Consider invasion of the oomycete Phytophthora in Australia: root parasite that kills weedy species. Herbaceous plants take over and smother seeds of woody plants; this changes the community of animals and other organisms too (e.g., grazers and plant-eating insects increase, but others decrease; nesting reduced, etc.).
3.3 “Snowballing” effect of invasion of an alien root pathogen (Part 1)
3.3 “Snowballing” effect of invasion of an alien root pathogen (Part 2)
Combined effects: Many island biotas decimated by both human effects via hunting and habitat destruction, and also introduced species (rats, pigs, goats...) that came with them. Hawaii: People killed off many native birds (largely for their feathers); many were ground nesters vulnerable to human-introduced species; few native predators before that. Plus anthropogenic habitat change.
Almost 90% of large mammal genera were lost in Australia after human colonization approx. 50,000 + years ago. Similar in North America, Middle and South America (10-15,000 years ago). May have been tied to climate change as well: warming 14-10,000 years ago, then glaciation in the North.
3.4 Mammalian megafaunal genera went extinct soon after human migrations
Extinction can be local (extirpation), global (lose entire species), or ecological (numbers reduced, can’t play key role in ecosystem; e.g., pollinator, top predator).
Extinction can also be “genetic”, or caused by change in genetic composition, especially loss in variation. Reduce population size and gene flow: genetic drift, inbreeding: “extinction vortex”.
3.5 Keystone and dominant species can have large impacts on biological communities
Sea otters: Prized for fur in 19th and early 20th centuries. Eat sea urchins in Pacific kelp forests. Sea urchin population exploded, and huge amounts of habitat for many species were lost.
Lose predators such as mountain lions and deer populations explode. Overgrazing, effects on habitat, less obvious effects. e.g., in central Texas, deer feed on bark tree that Golden-Cheeked Warblers use to make nests when other food is depleted.
Some species may not be abundant, but still very important: ”Keystone species”: effect on community disproportionate to numbers or biomass (e.g., top predators, pollinators, seed dispersers). ”Ecosystem engineers”: beavers, elephants.
Others dominate and shape the ecosystem: trees, corals, plants that prevent erosion, etc.. Also decomposers (bacteria, archaeans, fungi, and others): don’t often think of these.
Estimated numbers of globally threatened species: tracked by IUCN (International Union for the Conservation of Nature and Natural Resources): Red List. Levels of risk: Least Concern, Near Threatened, Endangered (there are subsets of these too).
41% considered Threatened to some extent; over 800 considered Extinct; a few only exist in captivity. Obviously a huge underestimate: focuses on known and conspicuous species, and how many do we have historical (or even much current) information on?
Threats: Biggest: habitat destruction, degradation, fragmentation (and can include pollution here). Includes migratory species: e.g., some birds, monarch butterflies (overwintering grounds; next figure is monarch butterflies). For some, overexploitation: e.g., fisheries.
Fall and spring migrations of the monarch butterfly
Forest cover has dropped dramatically within and adjacent to the three major monarch butterfly reserves
Worldwide, see the largest numbers of threatened species in areas of greatest species richness: moist tropical forest, tropical grassland; also montane regions (which may be especially affected by climate change).
Proportion of threatened species in North America (in the broad sense) is high, partly because of southern subtropical and tropical regions (and especially Hawaii). Plus, huge amount of agriculture, industry, urbanization, with a long history.
Plus, we know a lot more about North American species than those in SE Asia, Amazon, Africa, etc. -- there, many species are being lost before we even know about them.
3.7 Species richness of mammal, bird, and amphibian species in the major biomes of the world (black = threatened)
Threats in the U.S. by taxonomic group and category (next table): About 1200+ species are listed as Threatened or Endangered; some analyses suggest that up to 1/3 of U.S. species risk extinction.
U.S. started to address this relatively early: 1966: Endangered Species Preservation Act (native species). 1969: Endangered Species Conservation Act: extends protection to worldwide species (regulates imports etc.). 1973: Endangered Species Act (ESA).
ESA is more powerful than previous ones: extended protection to plants and invertebrates. Idea of “critical habitat” and more power to acquire land. Requires that all federal agencies follow the rules. Better integration with state conservation authorities, plus funding.
Various amendments: a key one is that economic concerns cannot take precedence over protection. Use biological, NOT economic information (rule isn’t always followed). Snail Darter in TN in 1970s: threatened by dam building: eventually exempted from ESA even though Supreme Court favored the fish.
Under ESA: Threatened: In danger of becoming Endangered. Endangered (imminent danger of extinction, with subcategories). Plus: Species of Concern: being watched closely.
Taxonomic patterns in the U.S.: lots of plants (but of course, there are lots of known species). However, freshwater species such as many invertebrates, fishes, and amphibians top the list, with (percent- wise) freshwater mussels worst off. Water resources are at great risk.
3.8 Proportion of species threatened with extinction by plant and animal groups in the U.S.
Elsewhere in the World: Number of species under threat largely correlated with amount of research: e.g., intensive study of plants in Ecuador, and many turn out to be at great risk. Similarly, Madagascar is a big focus: hugely deforested; more than 2/3 of plants and 1/3 of vertebrates are in serious danger.
China: Major problems: Habitat loss is a huge issue, but overexploitation is especially bad (food, medicine). Turtles: thought to prevent aging, cure cancer, etc. Some markets have literally tons for sale, and some are extremely valuable ($1,000s).
So many lost that now major imports from Vietnam, Indonesia, India, U.S., even Madagascar. Several species are known only from the markets; probably have (or had) very limited ranges; some don’t appear in markets any more.
Little chance of recovery: turtles are slow-growing, long-lived, usually age to maturity is long, not many offspring, often have specialized habitats and requirements. This also limits “farming” of many species (although becoming more economical). Similar issues with mammals, birds, non- avian reptiles.
3.9 Contribution of major threats to endangerment among vertebrate species in China
Recall that species richness increases with area: S = cA z, where S = number of species, A = area, and c and z are constants fitted to the data. On a log 10 scale, the relationship is positively linear with z (slope) ranging from about 0.15-0.35. So -- can predict the number of species lost with decreasing area.
Box 3.3 (A) Species–area relationships based on the equation S=cA z, with c=10
So, here, reducing an area of 1000, say, hectares to 100 should reduce the number of species by approx. 38% (z=0.20) to approx. 55% (z=0.35). Allows some prediction of effects of habitat loss, taking into consideration the kind of environment (considered as an “island).
Tropical forests: losing about 0.5% per year; assume that z = 0.2: then, about 0.125% of species lost per year. Suppose 5 million species; lose 6,000+ species/year.
Estimate (very rough) of the “background” rate of extinction is 10 species worldwide/year (tons of assumptions, and doesn’t include mass extinctions). Estimated current rate of species loss is much higher (50-10,000X).
Recovery rate (if factors causing extinctions stopped) can be very high. Fossil record and observations suggest that to regain the species richness of a lost coral reef could take up to 10 million years.
Vulnerability of species: Some have characteristics that make them more vulnerable than others. -need large area of contiguous / connected habitat (e.g., large mammals) -need limited type of habitat
-restricted to small geographic area -food specialization -codependence on other species, coevolution -low reproductive rate - rarity (discuss in a minute)
r vs. K selection: r-selected: often in unstable environments; reproduce at early age, lots of offspring, don’t invest much in them; most don’t make it but a few do. K-selected: longer-lived, slower maturation, fewer offspring but more investment in each, may not reproduce unless conditions are just right.
And, since generation times for K- selected species are longer, takes longer to adapt to changing conditions (plus not as wide a range of genetic variation in offspring). So: Habitat degradation, exploitation, etc. may lead to a shift to species that are r-selected; can change whole structure of ecosystem (and perhaps reduce richness).
What is “rarity”? Can mean lots of things. Widespread but not abundant in any one place. Abundant but very restricted distribution and/or habitat. Most vulnerable: Limited range, habitat specialization, small population sizes: threatened by catastrophe, exploitation, genetic deterioration.
Centinela Ridge (Ecuadorian Andes): RAP (Rapid Assessment Program) inventory 1980s: high levels of species turnover (high beta richness), many endemic species. Had at least 90 species of endemic plants; just after study finished, converted to agricultural land; all endemic plants went extinct. Common situation, especially in tropics.
“Artificial rarity”: Suppose that a species is widespread and abundant; then experiences reduced range and population size. May not be able to adapt to this (e.g., birds such as Passenger Pigeon that nested in huge numbers -- part of their life history). Or, loss of genetic variation.
In some cases, a species with specific habitat requirements and/or low population size may actually be better suited to some further reduction. And, if localized but widespread, may escape loss of at least some populations.
3.11 The Living Planet Index (LPI) tracks population trends for over 1100 vertebrates (Part 1)
3.11 The Living Planet Index (LPI) tracks population trends for over 1100 vertebrates (Part 2)
Prediction of threats to species and ecosystems: Biggest: Habitat loss, climate change, pollution. Overexploitation and invasive species lesser threats, but will increase, just not as fast.
The ONLY trend likely to slow is destruction of temperate forests. But this is just because most are already gone, and much of such habitat is in areas where people are affluent enough to preserve what’s left (or there just aren’t that many people/access difficult). Need education & creation of incentives.
3.12 Projected trends in threatening processes in different habitat types (Part 1)
3.12 Projected trends in threatening processes in different habitat types (Part 2)
Amphibian declines: Well studied; proxy for other groups too. Late 1980s: Biologists started to notice that various species of frogs and salamanders weren’t nearly as common as they used to be -- some even seemed to have disappeared. e.g., Golden Toad in Costa Rica; Gastric Brooding Frog in Australia.
And: Many of these declines were in seemingly pristine, relatively undisturbed areas (especially montane). Species-specific, but worldwide: Global Amphibian Assessment (mid-2000s and ongoing) found that about 1/2 of 400+ species that were declining fast were doing so for unknown reasons.
Most are tropical; South America and Australia best studied; particular groups of frogs seem especially vulnerable. Possibilities: 1)UV radiation: Bad for eggs of species that lay in areas of sunlight. May act together with parasites, acid rain: synergistic effects.
Depletion of ozone layer allows more UV-B through. Global warming makes breeding ponds shallower; less rain in some areas/more evaporation. Add acidification (and maybe toxins): features such as plants, microbes etc. change. Different plant composition: less shade.
Less water: amphibians congregate around water sources: greater spread of disease. 2) Disease: 1990s: chytrid “fungus” discovered that attacks amphibian skin -- seemed to correlate with declines in Australia and Central America. Slows growth rate of tadpoles/weakens or kills adults (maybe salamanders too).
Developed rapid PCR (polymerase chain reaction) test for chytrid-specific DNA: seems to be associated with some declines in N. America, Europe, other parts of the world. BUT: Present in some species without causing harm: natural resistance? Environmental interactions? Rare in tropical lowlands: does best in cooler temperatures.
Could be ancient, with cycles of epidemics? Maybe environmental stress makes some amphibians more susceptible? OR -- Could be new, and recently introduced to some amphibian populations (introduced species, humans, other carriers).
Disease cycles (in general) are normal, but why simultaneous declines worldwide and number of species affected in different habitats. PCR testing doesn’t show it in older museum collections: sudden appearance. Also -- very little chytrid DNA sequence variation -- suggests very little isolation, past or present; recent spread.
Maybe carried by introduced N. American bullfrogs and especially African Clawed Frogs (Xenopus) -- widely introduced around the world. And -- first documented in Xenopus, which appears to tolerate it well (perhaps coevolved mutualism or commensalism).
Other causes of declines: 3) Introduced species; e.g., trout stocking; accidental introduction of other species of fishes. Competition with/predation by other frogs: bullfrogs, marine toads, Cuban treefrog.
California: Introduced crayfish (fish bait) destroy eggs and larvae of salamanders that have natural skin toxins; crayfish are immune (crayfish are bad news in many areas). 4) Pollution: Some chemicals disperse even to remote areas: DDT, PCBs. Locally, atrazine (herbicide) causes sterility and developmental problems.
Pollution/acid rain may increase stress, susceptibility to other factors. Pollution and climate change can affect habitat: e.g., lose trees, less shading of streams, ponds (UV effects); disruption of fire cycles increases waterside vegetation, interferes with breeding migrations and metamorphic emergence onto land.
Amphibians likely are an indicator for more widespread issues, and illustrate interconnectedness of threats, as well as cumulative/synergistic processes. But -- sometimes hard to distinguish from natural population fluctuations -- gets tricky.
Case 3.1 (C) Fluctuations in population size of two species of salamanders in a temporary pond Grey = female; black = larval; 1=l
Madagascar: Huge biodiversity hotspot: many endemic species and groups (99% of amphibians, 93% of mammals). Separated from African mainland for approx. 160 million years; humans arrived about 2,000 years ago. Over 80% of native forest gone; extreme poverty, slash & burn agriculture, charcoal production.
Case 3.2 (B) Loss of forest cover on Madagascar
Native plants very sensitive to agriculture, grazing; soils low in nutrients; reduce forest cover and soil blows away. Intensive human predation, overcollection, many introduced species. Until recently, only 3% of land area protected.
Huge interest from international community: Intensive mapping, identification of “hotspots” of species richness, creation of national parks that maximize range of habitat types (or preserve unique ones). Work with local people to create incentives for conservation.
Cost/benefit analysis: Different scales: Geographic, political, economic. e.g., although timber harvesting creates many $$$ in the short term, most companies are foreign: most profits leave the country; forest is gone; industry leaves -- government gets some short-term benefit (a little bit to the average person) but short-sighted.
In the long term sustainable harvest is better, even just economically (within the country). Global impications: Forest removes lots of carbon from the air: world value about $500 million/year. Split incentive: How to convince Madagascan government to preserve forests and create/maintain parks?
International governments have given $ millions, but payback has been huge: protection of drinking water, erosion, establishment of ecotourism, etc. Improvements (as of mid-2000s): rate of forest loss declined to about 1/20th that in mid-1990s; burning has dropped to about 1/16th; some ecosystems recovering (e.g., coral reefs affected by runoff).
Slash & burn agriculture and charcoal production still a problem: agricultural land only has enough nutrients for 2-3 years, then move on; also, still too much logging. But: Help from outside to establish sustainable logging, ecotourism; improve relations between government and local peoples (put locally generated $$$ into local economies; education + technology.
Social sustainability: Establish systems to oversee the process and ensure continued benefit of local peoples: as people see the benefits, the idea spreads. Not perfect, but a model for conservation elsewhere in the world.
Chapter 4: Conservation Values and Ethics We’ll only cover this briefly, and introduce some key points that will come up again.
Distinguish between instrumental (utilitarian) value -- what good can biodiversity do for humans? And: Intrinsic value: Inherently valuable, whether or not useful to humans (biocentric/egocentric view).
Norton’s (1991) convergence hypothesis: Idea that anthropocentric (human- centered) “instrumental values” intersect with non-anthropocentric “intrinsic values” (and pure intrinsic value ideas can actually be damaging to the case for conservation). Anthropocentrism covers a lot of ground, from goods and services to spiritual meaning.
Taylor’s (1986) biocentrism: All organisms are inherently valuable, even individuals. But how to apply? And how does this relate to ecosystems etc.? Rolston (1994) added a more complex “moral” dimension: aggregates (ecosystems, evolution itself, etc.) are worth more than species, for example. Sentient beings are worth more than non-sentient ones.
Chapter 5: Ecological Economics and Nature Conservation Obviously, people will always need/want resources; a tradeoff; often requires sociological, anthropological, political, and economic perspectives.
No simple answers -- but what if you can put a price on conservation? Madagascar: Can place a monetary value on reduction of atmospheric CO 2. Economists try to assess the effects of one set of actions versus another on human interests. Usually money is the measure.
Concept of utility: “Wellbeing”: How much does the average individual benefit? And how do they benefit? Higher income, happiness from enjoying biodiversity, quality of life/health (e.g., reduced pollution). One way to assess utility: how much will people pay for something?
Text example: Buy a drink; how much will you spend? A lot: Net loss in utility (unless it really meant a lot e.g., extreme thirst); get a good deal: gain in utility. Often tradeoffs.
Road construction project: Try to increase or at least balance utility; people may be willing to accept something that improves their utility in exchange for less or no construction (e.g., drive further, but less pollution/noise). Some of this is unmeasurable (at least directly).
But some is measurable: e.g., park land, hunting, fishing, clean water, health costs of pollution, clean water, house prices -- things that can affect the local economy. Is the utility higher or lower once the project is completed? If lower, is there compensation for lost utility (more jobs, less transit time, some other recreational area set aside...)?
Cost-benefit analysis (CBA): Many aspects of utility are intangible, even philosophical: how to quantify? “Ecological economics”. 1981: U.S. Presidential Executive Order requires CBA for new policies/projects. What’s best for society as a whole?
Of course, not everyone will benefit. But, a CBA has the “hypothetical consent of the citizenry”: elected officials should implement policies that public perceives improve social welfare. CBA has 5 steps.
1)Project definition: What is the project and how will its utility be assessed? Suppose an oil company wants to build an oil rig. Goal: Increase profits. Costs to company: construction, oil yield, oil prices. Environmental concerns probably less (although do have to consider PR costs).
The government “should” look at the other side of things: tradeoffs to public welfare. And, what are the “boundaries of inquiry” (just like the oil company does)? = how many factors to consider? Of course, government doesn’t always have opposite interests, and decisions have to be structured at different levels, e.g., local vs. national.
2) Impact classification: For the company, the costs etc.; for the public, employment, local economy, also environmental costs for life of oil rig. Consider immediate and long-term costs/benefits. What impact will the project have on the environment?
Have to consider what might happen versus what’s likely to happen anyway. Consider example of a rare species of finch whose breeding habitat will be impacted by construction. 30% of breeding habitat will be lost: raises chance of extinction in 100 years from 10% to 30%.
BUT: Oil company looks at migration: 70% of migratory habitat estimated to be gone in 10 years. So even without oil rig, chance of extinction is 10% + 70% = 80%. Can’t do anything about what’s happening in winter migration area. Suppose their calculations say that building will only increase chances of extinction to 81%.
Assuming that the data are accurate, the cost/benefit ratio in terms of the bird hardly changes with or without construction. (Of course, here no direct economic value is assigned to the bird, but for other aspects of the environment there could be).
5.1 Two views of the impacts of a hypothetical project
3) Conversion to monetary terms: Above, no dollar value assigned, and wouldn’t matter much anyway. Usually though, need some uniform scale (usually $$$). Construction costs are “market goods” (can be bought). Some environmental factors are also marketable.
e.g., fishing, hunting etc. Many environmental factors are “nonmarket” but valuable: reduced pollution, ecotourism (actually does have some market value), role of species in ecosystem that has measurable effect on humans, etc. But can’t (usually) put a price on enjoying nature.
But, at least a CBA provides some baseline that forces the government to consider local economy and other concerns, and the environment. Assessing value of biodiversity: use vs. non-use values. Use: fisheries, timber, etc.; indirect use: clean water, shade prevents drying = long and short-term ecosystem services.
5.3 Total economic value of wetlands is composed of direct, indirect, option, and nonuse values
Ecosystem services: Indirect use; often hard to quantify. e.g., decomposition of organic wastes: about 38 billion tons created per year: breakdown by microbes, fungi etc. frees space, recycles nutrients, prevents disease/pollution. Estimate of total value of ecosystem services to US per year: $33 trillion (especially wetlands).
5.4 Nonmarket values of forest can be substantial
Non-use: No simple good-to-consumer relationship; factors such as pleasure people get from nature = loss of utility; bequest value (passing on to future generations). Add up total use and nonuse values: Total Economic Value (TEV).
Historically, nonuse values have been a small (or no) part of TEV; now becoming a bigger part of the equation. Various ways to convert value of biodiversity to money terms.
Substitute value: e.g., how much would it cost to buy local vs. foreign wood? Product function approach: Suppose that a change in environment causes a measurable change in productivity (e.g., desertification). Opportunity cost: Alternate use value (e.g., national park value vs. logging).
Implicit market techniques: How people act reflects the value that they place on the environment: where they live, vacation, etc. “Hedonic” pricing methods: Sum total value of a product (or ecosystem) based on all individual factors, and how does it change if one or more of the factors is varied?
One measure: property values. How much will people pay to live in a fairly natural area vs. a cleared one? (a hedonic variable). But often difficult to assess all the nonuse factors. Travel cost: How far, and how much will people pay, to visit, say, a national park?
What is a species or ecosystem worth? Contingent valuation approach: How much will people pay to conserve something (WTP = “Willingness to pay”). Simulate a market for the species or ecosystem: how much will people pay to protect it? Depends on the individual and the population.
Consider Sri Lankan Sinharaja Forest: Estimated TEV via WTP approach. -Villagers on edge of forest -More distant rural people -Sri Lankan urbanites -UK urbanites In absolute $$$, richer people would pay more to preserve. But relative to income, villagers who use the resource would pay the most.
5.4 Nonmarket values of forest can be substantial
How good is the average person at estimating value of an ecosystem or species? Survey of coastal and mountain areas in Scotland: Scientists assessed species richness/diversity, rarity, distributions; then ranked in terms of conservation priority. Then asked the public their WTP for each area -- very different result.
So -- have to balance conservation priorities and satisfying the public, who may value the resources differently.
Recall CBA: 1)Project definition 2) Impact classification 3) Conversion to monetary terms 4) Project assessment: Assemble all the information in the context of the above, and also consider the time frame.
Next table: Developer builds factory, breaks even in 10 years, and makes more money in the long term. But -- Environmental cost is high: habitat destruction, pollution -- undesirable from conservation standpoint. Politicians look at other costs/benefits, including effect on local economy as well as environment.
Short term: Economic benefits outweigh environmental costs. But in the long term, environmental costs become greater. Of course, this may not matter so much to a politician. And consider discount rates -- actual $$$ depreciate, whereas environmental value may be more constant.
5.5 Example of how the net present value of a sum varies over 100 years
Last step of CBA: 5) Sensitivity analysis: Given cost/benefit estimates, how sensitive are these estimates to changes in parameters: e.g., product demand, need for clean water. Can run simulations under different scenarios.
Problems with CBA: -Uncertainty of estimates themselves (especially environmental). -Defining bounds of inquiry. - Who benefits -- is it really “all” of society?
Case 5.1 (A) The protected area network in Uganda in the mid-1990s
Other approaches: Environmental Impact Assessment: Focus on probable environmental results of project, either as part of CBA or separately. Often not done very well.
Risk assessment/management: What is the chance of a hazard; negative results. What is the potential magnitude of a negative result? Can express mathematically; e.g., wind farm (electricity): may kill birds, bats, etc.; depending on level of risk, may cancel or relocate.
Many kinds of risk assessment, e.g., use of pesticides; intensity of fishing. Once probability of a given risk is calculated, have to decide what’s acceptable. e.g., if harvest of 100 tons of fish/year is allowed but this has a 1% chance of destroying the fishery, is it worth it?
How does the public perceive the risk? Similar to a CBA; some things are worth more risk than others; e.g., if only a few fishermen and not a really in- demand species, reduced catch may be OK; if this is a main food source for a growing population, may be willing to take more risk.
Precautionary principle: Despite risk assessment, can’t predict all negative outcomes (e.g., a medication that seems safe may cause cancer later in life; effects of DDT on things like bird eggshells only discovered after years of use and the chemical had gone up the food chain).
But how many things to test? Good example: GMOs (genetically modified organisms). Many people are afraid of these, and there are legitimate concerns. But many of these could have real environmental benefits; e.g., drought resistance in crops.
So is it better to do nothing? Of course not -- but have to assess how much testing to do. Multi-criterion analysis: Pull together info. from various kinds of analysis (sort of a “meta-analysis”) to find optimal solution.
e.g., what approach is most likely to preserve habitat, minimize pollution, etc.; environmental vs. socioeconomic benefits, for example.
Nonsubstitutability: What features of the environment absolutely have to be protected (for practical or philosophical reasons)? -Ozone layer -Global warming “Critical natural capital”.
Are some species or ecosystems better or more important than others? Don’t know how many fit in -- so here the precautionary principle comes into play.
“Rivet hypothesis” (not in text): Suppose that for a plane, losing one rivet doesn’t matter much, but two...three...ten... (and what part of the plane may matter too). At some point the whole thing falls apart. How many “rivets” (species/ecosystems) can we afford to lose? Critical reserves: try to save everything in a given area -- but practical?