40 Population Ecology and the Distribution of Organisms.

40 Population Ecology and the Distribution of Organisms

ECOLOGY Ecology: the study of relationships of organisms to one another and to their environment Abiotic factors: physical factors, such as climate, nutrient availability Biotic/biological factors: competitors, predators, parasites, prey

Figure 40.2 Global ecology Ecological Research Ecologists study interactions from the scale of individual organisms to the entire globe Landscape ecology Ecosystem ecology Community ecology Population ecology Figure 40.2 Exploring the scope of ecological research Organismal ecology © 2016 Pearson Education, Inc.

Organismal Ecology Organismal ecology considers how an organism’s structure, physiology, and behavior meet environmental challenges Organismal ecology includes physiological, evolutionary, and behavioral ecology © 2016 Pearson Education, Inc. 4

Figure Population Ecology Population ecology considers factors affecting population size over time A population is a group of individuals of the same species living in an area Figure Exploring the scope of ecological research (part 2: population) © 2016 Pearson Education, Inc.

A community is a group of populations of different species in an area
Figure Community Ecology Community ecology considers the whole array of interacting species in a community A community is a group of populations of different species in an area Figure Exploring the scope of ecological research (part 3: community) © 2016 Pearson Education, Inc.

Figure Ecosystem Ecology Ecosystem ecology emphasizes energy flow and chemical cycling among the various biotic and abiotic components of the environment An ecosystem is the community of organisms in an area and the physical factors with which they interact Figure Exploring the scope of ecological research (part 4: ecosystem) © 2016 Pearson Education, Inc.

A landscape (or seascape) is a mosaic of connected ecosystems
Figure Landscape Ecology Landscape ecology focuses on the exchanges of energy, materials, and organisms across multiple ecosystems A landscape (or seascape) is a mosaic of connected ecosystems Figure Exploring the scope of ecological research (part 5: landscape) © 2016 Pearson Education, Inc.

Biosphere: the sum of all of the planet’s ecosystems and landscapes
Figure Global ecology Global ecology examines how the regional exchange of energy and materials influences the functioning and distribution of organisms across the biosphere. Biosphere: the sum of all of the planet’s ecosystems and landscapes Figure Exploring the scope of ecological research (part 6: global) © 2016 Pearson Education, Inc.

Concept 40.1: Earth’s climate influences the distribution of terrestrial biomes
The long-term prevailing weather conditions in an area constitute its climate 4 physical components of climate: temperature, precipitation, sunlight, and wind © 2016 Pearson Education, Inc. 10

Global Climate Patterns
Global climate patterns are determined largely by solar energy and the planet’s movement in space The warming effect of the sun causes temperature variations, which drive evaporation and the circulation of air and water This causes latitudinal variations in climate © 2016 Pearson Education, Inc. 11

Latitudinal variation in sunlight intensity is caused by the curved shape of Earth
Sunlight strikes the tropics, regions between 23.5 north and 23.5 south latitude, most directly At higher latitudes, where sunlight strikes Earth at an oblique angle, light is more diffuse © 2016 Pearson Education, Inc. 12

Low angle of incoming sunlight
Figure Atmosphere 90N (North Pole) Low angle of incoming sunlight 23.5N (Tropic of Cancer) Sun overhead at equinoxes 0 (Equator) 23.5S (Tropic of Capricorn) Figure Exploring global climate patterns (part 1: latitudinal variation in sunlight intensity) Low angle of incoming sunlight 90S (South Pole) © 2016 Pearson Education, Inc.

Labrador Current California Current Gulf Stream PACIFIC OCEAN ATLANTIC
Figure 40.5 Labrador Current California Current Gulf Stream Figure 40.5 Circulation of surface water in the oceans around North America PACIFIC OCEAN ATLANTIC OCEAN © 2016 Pearson Education, Inc.

SOLAR RADIATION Major determinant of Earth’s surface temperature: the angle at which solar radiation strikes the surface. Earth climate: hot near the equator and cold at the poles; this reflects incoming solar radiation. Sunlight strikes equatorial regions directly, but at higher latitudes, Earth’s surface is tilted at an angle to incoming radiation. At higher latitudes, temperature is not only lower, it also exhibits greater variation through the year. Seasonality: reflects a second feature of Earth Earth’s axis of rotation is not oriented perpendicular to incoming sunlight but rather tilts at an angle of 23.5 degrees This is why most parts of globe show seasonal variation of temperature.

Annual Mean Temperature
Climate The latitudinal difference in incoming solar energy density explains why Earth’s surface is hotter at the equator and cools towards the poles. ~1000 km ~2000 km Annual Mean Temperature 60˚ 30˚ 0˚ At the equator, solar energy strikes Earth directly, resulting in high influx of energy per unit area. At high latitude, incoming solar energy strikes Earth at an angle, resulting in lower fluxes of energy per unit area. Solar radiation North pole South pole The principal control on Earth’s surface temperature is the angle at which solar radiation strikes the surface. Earth is the Goldilocks planet: just the right distance from the sun so that, in conjunction with the greenhouse effect of the atmosphere, solar radiation maintains surface temperatures that can keep water in its liquid form. At first glance we see that Earth is hot near the equator and cold at the poles. This temperature distribution reflects incoming solar radiation. Sunlight strikes equatorial regions directly, but at higher latitudes, Earth’s surface is tilted at an angle to incoming radiation. At higher latitudes, temperature is not only lower, it also exhibits greater variation through the year. Seasonality reflects a second feature of Earth as a planet: Earth’s axis of rotation is not oriented perpendicular to incoming sunlight but rather tilts at an angle of 23.5 degrees.

BIOMES Temperate Grassland Desert Tundra Chaparral Alpine Talga
Biomes are broad, ecologically uniform areas characterized by their climate, soil, and plant/animal species. Temperate Grassland Desert Chaparral Savanna Rain Forest Tundra Alpine Talga Temperate Coniferous Forest Deciduous Forest Populations are dynamic, continually increasing and decreasing in response to local physical and biological influences. Communities and ecosystems are also dynamic, with species coming and going as a result of disturbance and succession. Nevertheless, the assemblages of species found over broad regions of Earth are both distinctive and stable. Such broad, ecologically uniform areas are called biomes. On land, different biomes are recognized by their characteristic vegetation, which reflects the evolutionary adaptation of form and physiology to climate. Terrestrial biomes range from the low-growing tundra found at high latitudes to tropical rain forests, and from grass dominated steppes and deserts to coastal estuaries. Biomes occur in the oceans as well as on land, and the largest and least-understood biome of all is the vast expanse of cold dark water in the deep sea.

Terrestrial Biomes Primary producers: mainly vascular plants
In terrestrial biomes, vascular plants dominate primary production, although mosses, lichens, algae, and cyanobacteria also contribute. Plants also provide a physical structure for the biome, with high canopies in wet temperate forests and tropical forests, but shorter vegetation where water or nutrients are scarce, or where the growing season (the part of the year when temperature and precipitation permit plant growth) is short. Primary consumers include a variety of animals, but in many environments, mammals and insects are the principal herbivores, grazing on leaves, fruits, seeds, and stems. Terrestrial biomes are often characterized by the carnivorous vertebrates that live there, which are among the most charismatic of all animals—for example, lions, tigers, and wolves. Primary producers: mainly vascular plants Plants also provide a structure for these biomes Primary consumers: variety of animals; mammals, insects Secondary consumers: carnivorous vertebrates….lions, tigers, wolves

Tropical Rain Forest Humans: Development destroying many rain forests
Moist, highly diverse forest North and south of the equator from 10o N-10o S Very hot and heavy rains Huge tree diversity; very tall, epiphytic plants common Decomposition rapid Primary consumers: smaller primates, bats, rodents, birds, snakes, lizards Insects are especially abundant and diverse Ants make up 30% of animal biomass here This moist, highly diverse forest extends north and south of the equator from 10°N to 10°S. Annual precipitation is commonly more than 250 cm, and tree diversity alone often exceeds 300 species per hectare. Trees grow tall, and many have buttressed roots for support. Lianas and other epiphytic plants are common. Most leaves are evergreen and leathery and many have long pointed tips that facilitate drainage of excess moisture. Because of the high temperatures and heavy rains, decomposition is very rapid, preventing the accumulation of organic materials in clay-rich or sandy soils. Humans: Development destroying many rain forests

Tundra Close to North Pole, above 65o degree N Coldest biome
Permanent ice below soil Low plant diversity…mainly mosses, lichen, herbs Primary consumers: caribou, rabbits, birds Secondary consumers: wolves, foxes Humans: Sparsely settled. Significant mineral & oil extraction Tundra occurs close to the North Pole, above 65°N. The South Pole is largely surrounded by the ice and seas of Antarctica, and so there is very little area with plants. Tundra is the coldest biome, and precipitation and evaporation are minimal. Even with little precipitation, the lack of evaporation and drainage means the ground is usually waterlogged, and permanent ice occurs below a few centimeters of soil. The plants are mostly mosses, lichens, herbs and low shrubs. Grasses and sedges occur in drier places, as do other flowering plants. Plant diversity is low, and most plants are small.

Alpine Similar to tundra, but lacks permanent ice below soil
Found throughout world at high altitudes (10,000 ft, but just below snow line) Windy and cold Low and slow-growing plants Primary consumers: mountain goats, llamas, yaks The Alpine biome is similar to tundra but lacks permanent ice below the soil, and the temperatures vary more widely. Alpine areas occur throughout the world, often at about 10,000 feet at lower latitudes, but always just below the snow line. Because of their altitude, these are windy, cold places. The thin atmosphere provides only limited protection from UV radiation. Many Alpine plants are therefore low and slow growing.

Taiga Humans: Logged at a very fast rate
Cool, moist forests at degree N Plants are conifers Soils deep with accumulated organic matter….acidic and poor in nutrients Primary consumers: elk, moose, caribou, porcupines Secondary consumers: bears, lynx, wolves, foxes Humans: Logged at a very fast rate These cool, moist forests occur from 50° to 65° N. The short summer brings rain, and most of the plants are conifers like spruce, fir, larch, and pine, with an understory dominated by shrubs in the blueberry and rose families. The soils are deep with accumulated organic matter because the low temperatures result in slow decomposition, but they are acidic and poor in nutrients.

Temperate Coniferous Forest
Occur below 50 degrees N Temperate with much precipitation North America, northern Japan, parts of Europe, and continental Asia Enormous conifers along Pacific coast of US; undergrowth is ferns Insect and vertebrate diversity : higher than taiga forests Humans: Heavily settled globally. Destryoted by logging and clearing for agriculture Two broad areas of temperate coniferous forests occur below 50°N in North America, northern Japan, and parts of Europe and continental Asia. Along the Pacific coast of the United States, abundant precipitation permits growth of enormous conifers such as Douglas Fir, Red Cedar, Sitka Spruce, and redwoods. Much of the undergrowth is ferns and members of the blueberry family. In the interior of North America, much less precipitation and colder winter temperatures support drought-resistant conifers such as Ponderosa and Lodgepole Pines and Englemann Spruce.

Deciduous Forest Across much of North America, Europe and Asia
Moderate climate Hardwood deciduous trees……maples oaks, poplar, birches Human disturbance from agriculture and urban development Much organic soil Insects, birds and mammals are diverse; also snakes, lizards, and amphibians A moderate climate and dominance of hardwood deciduous trees occurs across much of North America, Europe, and Asia. Much of this biome has been subjected to human disturbance for agriculture and urban development. There are usually 15–25 species of trees, including maples, oaks, poplars, and birches. Springtime sun passes through seasonally leafless trees to reach a diverse understory flora. Soils are rich in nutrients from annual leaf fall, and the moderate temperatures and precipitation promote decomposition, while the cool winters promote accumulation of organic materials.

Temperate Grassland Occupied most of Midwestern US prior to settlement Mainly grasses Fire maintains grass population Soils accumulate nutrients; most productive agricultural lands in the world Before colonization by humans: bison, horses, mammoths Now, burrowing grazers such as prairie dogs are common Secondary consumers: ferrets, badgers, foxes, birds of prey Humans: Been converted to farmland. In some places, cattle turned it into desert. Before settlement, this biome occupied most of the midwestern United States, where it is dominated by blue-stem and buffalo grasses. Fire helps to maintain grass populations in this biome. Lack of precipitation prevents many species of tree from growing, and those trees that grow are usually in low areas with some moisture. Where there is enough moisture to support decomposition, the soils accumulate nutrients, providing some of the most productive agricultural lands in the world.

Desert Around the world north and south of equator from 25o -35o.
Windy; little precipitation Deep-rooted plants adapted to store water, i.e. cactus Primary production is low; Soils poor in nutrients, but high in salt Primary consumers tend to be small….diverse lizards, rodents Secondary consumers: snakes, coyotes, cat species, birds Humans: Urbanization & conversion to irrigated agriculture have reduced biodiversity Desert occurs in continental interiors around the world north and south of the equator from 25° to 35°. Wind patterns prevent this biome from receiving more than a few centimeters of precipitation annually. The deep-rooted plants are adapted to store water, like cactus and euphorbia. Primary production is low, and soils are poor in nutrients but may have high surface salt due to evaporation.

Chaparral Narrow range of climate conditions Occurs on western edge of continents from 32o-40o north and south of equator Limited rain and falls in 2-4 months Plants are annual herbs, evergreen shrubs, and small trees Drought resistant trees, fire resistant Poor nutrients in soil Humans: Heavily settled. Reduced through conversion to urbanization and agriculture. Fire problem. Like deserts, the distribution of chaparral reflects a narrow range of climate conditions, and occurs on the western edge of continents from 32° to 40° north and south of the equator. Precipitation ranges from 30 to 75 cm per year, usually falling in 2–4 months. Typical plants are annual herbs, evergreen shrubs, and small trees. Olives, eucalyptus, acacia, and oaks are typical woody species, always drought resistant and often adapted to withstand fire. Limited precipitation means soils are not rich in organic materials.

Savanna Eastern Africa, southern South America, Australia Tall, perennial grasses Rain is seasonal Scattered trees and shrubs Animal diversity is high; Primary consumers: antelopes, zebras, giraffes, kangaroos, large rodents Secondary consumers: lions, other cat species, hyenas, wild dogs, dingoes, snakes Humans: Earliest humans lived here. Overly frequent fires set by humans reduce tree regeneration. Cattle ranching & overhunting have led to declines in large mammal populations. Tall, perennial grasses dominate this biome, which occurs in eastern Africa, southern South America, and Australia. Rain is seasonal and ranges from 75 to 150 cm per year. Scattered trees and shrubs usually drop their leaves in the dry season to conserve moisture. Animal diversity can be high and includes the large mammals well known in Africa.

Concept 40.2: Aquatic biomes are diverse and dynamic systems that cover most of Earth
Aquatic biomes are characterized primarily by their physical and chemical environment Marine biomes have saltwater concentrations that average 3% Freshwater biomes have salt concentrations of less than 0.1% © 2016 Pearson Education, Inc. 29

Aquatic Biomes Solar radiation Oceanic system Neritic system
Pelagic realm Photic zone Average depth 200m Well-mixed water Deep seafloor Continental slope Continental shelf Aquatic biomes reflect climate, and also the availability of nutrients and oxygen and the depth to which sunlight penetrates through water. In shallow aquatic environments such as lake margins and coastal marine settings, much plant, algal, and animal debris accumulates in sediments, supporting luxuriant growth by bacteria. Grazers such as snails and fish feed on marginal plants and algae, while single-celled protists and microscopic animals called zooplankton consume phytoplankton that floats in the water. As on land, secondary consumers such as other fish or squid feed on the grazers, adding complexity to food webs. Because oxygen gas dissolves in water only to a limited extent, surface waters directly beneath the atmosphere will have an O2 concentration about 20 times lower than that of the air. This compels larger animals to be moving constantly to keep their gill systems well-oxygenated, or to live in places such as cold running streams and rocky marine coastlines where currents naturally produce well-oxygenated water.

Aquatic Biomes Only about 2.5% of water is fresh: lakes and rivers, glaciers, permafrost, groundwater in soil 71% of Earth’s surface is seawater Ocean is the largest biome The main freshwater biomes are lakes and rivers. In general, the turbulent flow of water ensures that rivers are well-oxygenated. Some lakes, however, are physically stratified, meaning that the density of bottom waters keeps them from mixing upward with shallow waters. Organic remains that sink to deep waters provide food for respiring bacteria, and this draws down oxygen levels. Where nutrient influx is high, such lakes can become anoxic in their deeper parts; this is particularly common where human activities have increased nutrient loads entering the lake. Only about 2.5% of Earth’s water is fresh, and most of this water occurs in glaciers, permafrost, and groundwater within soils. Overwhelmingly, the water on our planet is seawater. Covering 71% of Earth’s surface and reaching a depth of nearly 11,000 m (almost 7 miles), the oceans constitute Earth’s largest biomes.

Lakes Range in size from tiny pools to the Great Lakes (has more than 20% of all freshwater) From equator to about 80 degrees N Primary producers: algae, cyanobacteria Zooplankton (heterotrophic or detritivorous organisms drifting in aquatic biomes): small arthropods and rotifer protists Nekton (all aquatic organisms that can swim freely and independent of currents): fish Secondary consumers: turtles and birds Humans: Dumping of wastes lead to nutrient enrichment, which can produce algal blooms and fish kills. Lakes and ponds range in size from tiny temporary pools to the Great Lakes of North America, which contain more than 20% of all freshwater habitats in the world. They range geographically from the equator to above 80° N. Their chemistries vary with the types of terrain in which they are found, and nutrient levels can be low to extremely high. Aquatic plants and macroscopic green algae live along the shallow margins of lakes, and both algae and cyanobacteria are primary producers throughout the photic zone. Zooplankton include small arthropods and rotifers, whereas the nekton is dominated by fish. Turtles and birds also play an important role as grazers and predators in many lakes.

Rivers Freshwater biomes characterized by moving water
Primary producers: plants and large algae, phytoplankton Primary consumers: insects, fish, turtles, birds Salmon: spend lives in oceans, but swim up rivers to reproduce Humans: Pollution degrades water quality and can kill aquatic organisms. Dams hurt the natural flow of streams/rivers and threaten migratory species such as salmon. Rivers are freshwater biomes characterized by moving water. Rivers and streams, like lakes, vary tremendously in size and chemistry. Because of currents, rivers are generally well-oxygenated, although oxygen levels may be lower in slowly moving rivers on floodplains. As with lakes, plants and large algae grow along river margins, while phytoplankton photosynthesize throughout the water column. Insects are important consumers, but other invertebrates, fish, turtles, and birds can all be abundant and diverse. Salmon and some other fish spend much of their lives in the oceans but swim up rivers to reproduce.

Intertidal Zone Lies along coastlines between high and low tides
Organisms are exposed to the atmosphere on a daily basis Waves can cause mortality; so algae and animals securely attached to substrate Consumers: sea stars, sea urchins, mollusks, barnacles, corals Humans: Oil pollution has hurt these areas. The intertidal zone lies along coastlines between mean high and low tides, meaning that organisms in this biome are exposed to the atmosphere on a daily basis. In sandy intertidal zones, or tidal flats, many animals burrow into the wet sand to escape exposure at low tide. In rocky intertidal zones, organisms may close their shells tightly—for example, mussels and barnacles. Waves can cause mortality, as well, and so, especially along rocky coastlines, both algae and animals are securely attached to the substrate. Nutrient levels can be high, favoring strong algal growth. Consumers include a variety of sea stars, sea urchins, mollusks, barnacles, and corals.

Coral Reefs Best known reefs occur in shallow, tropical to subtropical saltwater environments with little water movement Primary production: dinoflagellate algae that live within tissues of corals Free-living algae occur in reefs, but kept low by grazing fish Many species invertebrates also live in coral heads Fish diversity especially high Coral reefs also occur in deep sea, but build gradually since coral growth is slow in absence of symbiotic algae The best-known reefs occur in shallow, tropical to subtropical environments where there is little water movement or accumulation of sand or mud, with the accumulating skeletons of corals building a structure above the seafloor. Nutrient levels are commonly low, but primary production is high and mostly tied to dinoflagellate algae that live within the tissues of corals. Free-living algae occur in reefs, but are kept at low abundance by grazing fish. Many species of invertebrates live within the reefs, often in nooks and crannies among coral heads that provide shelter from predators. Fish diversity can be especially high. Coral reefs also occur in the deep sea, but build gradually, as coral growth is slow in the absence of symbiotic algae. Humans: Overfishing has led to reduced corals and reef fishes. Global warming and pollution may be contributing to large-scale coral death.

Pelagic Realm The part of the ocean neither close to shore nor close to seafloor: forms bulk of ocean Organisms live within the water column: either as zooplankton (tiny arthropods)or nekton(cephalopods) Upper region with sunlight: primary producers are diverse algae and cyanobacteria Secondary consumers: fish, squids , heterotrophic protists Humans: Overfishing has depleted fish stocks, which have also been affected by climate warming and pollution. The pelagic realm—the part of the ocean that is neither close to shore nor close to the seafloor—forms the bulk of the oceanic system. Organisms live within the water column, either as plankton or nekton. In the upper 200 m or so of the pelagic realm, sunlight permits photosynthesis, with diverse algae and cyanobacteria as primary producers. In deeper waters, however, sunlight is absent and life is sustained by the rain of organic particles from surface waters. Minute arthropods dominate the zooplankton, while fish and cephalopods are key components of the nekton. Fish and squids are conspicuous consumers, but recent research shows that in the upper water column, heterotrophic protists may actually be more abundant and diverse.

Deep Sea The deep seawaters: cold and dark High species diversity
Primary producers: chemosynthetic bacteria Primary consumers: bacteria, archeons; sinking detritus Dense animal populations occur on deep seafloor in location of hydrothermal vents Humans: Overfishing has destroyed fishes, such as the cod of the Great Banks off Newfoundland Dumping of organic wastes has created oxygen-deprived areas.. Kilometers below the surface, deep seawaters are cold and dark, but they are not sterile. Sinking detritus supports sparse populations of animal consumers, as well as bacteria and archaeons that feed on organic particles. Despite their limited biomass, deep-sea biomes exhibit high species diversity, as high as those of shallow marine communities. However, the composition of communities in deep sea biomes differs relatively little from place to place, and so the total diversity of these environments is lower than that found within the photic zone. Dense animal populations occur locally on the deep seafloor where hydrothermal vents expel fluids containing high abundances of hydrogen, hydrogen sulfide, and methane. These compounds support locally high levels of primary production by chemosynthetic bacteria, many of them present as symbionts within the tissues of vent animals.

POPULATIONS & THEIR PROPERTIES
46.1 A population consists of all the individuals of a given species that live and reproduce in a particular place. A population is characterized by: Size: number of individuals at a particular time and place Range: total area in which a population lives Density: population size divided by range Population size estimates: sampling & mark-and-recapture techniques

POPULATION Size Range Density
Their range is approximately 19 million square kilometers in the Southern Ocean. Range Density 800 trillion krill over 19 million square kilometers of the Southern Ocean means the population density is 42 million animals per square kilometer on average. Mean no. krill/km2 <2 2-4 4-8 8-16 16-32 32-64 64-128 >512 The size of the Antarctic population of krill is estimated to be 800 trillion animals. Size Ecology is the study of the relationships of organisms to one another and to the environment. Ecological relationships sustain a flow of energy and materials from the sun, Earth, and atmosphere through organisms, with carbon and other elements eventually returning to the environment. In previous chapters, we discussed the anatomical, physiological, reproductive, and behavioral characteristics of organisms. These attributes are the products of evolution, and they determine the ways in which individual organisms interact with their physical and biological environment. Physical or abiotic factors that influence evolution include climate and nutrient availability; biotic factors include competitors, predators, parasites, and prey, as well as organisms that provide shelter or food. Ecology and evolution, then, are closely intertwined.

Key Features of a Population
Their range is approximately 19 million square kilometers in the Southern Ocean. Range Density 800 trillion krill over 19 million square kilometers of the Southern Ocean means the population density is 42 million animals per square kilometer on average. Mean no. krill/km2 <2 2-4 4-8 8-16 16-32 32-64 64-128 >512 The size of the Antarctic population of krill is estimated to be 800 trillion animals. Size A population consists of all the individuals of a given species that live and reproduce in a particular place. Natural selection enables populations to adapt to the physical and biological components of their environment. Populations are defined by three key features: size, range, and density. Population size is the number of individuals of all ages alive at a particular time in a particular place. For example, the population of krill around Antarctica is estimated to be 800 trillion.

Estimating Population Size
The distributions of individual trees or other organisms can appear to be random, with no clear pattern to where they occur. If resources are clustered or spatial proximity to other individuals enhances fitness, populations may be clustered. When resources are limited or predators target a single species, an individual might be better off if it is as far from others as possible, producing a uniform pattern of distribution. a. b. c. Estimating Population Size Ecologists estimate population size by taking repeated samples of a population and from these samples estimating the total number of individuals. With an estimate of population size and range, ecologists can then determine population density. For sessile, or sedentary, organisms like milkweeds in a field or barnacles on a rocky shoreline, ecologists commonly lay a rope across the area of interest and count every individual that touches it, or they throw a hoop and count the individuals inside it. For mobile organisms, such as turtles, a method called mark-and-recapture is useful. Biologists capture individuals, mark them in a way that does not affect their function or behavior, release them back into the wild, and then capture a second set of individuals, some of which were previously marked.

POPULATION GROWTH AND DECLINE
46.2 Population size can increase or decrease over time Population size influenced by: Births Deaths Immigration emigration

Factors Affecting Population Size
Mortality (death) and emigration both contribute to population decrease. Birth and immigration both contribute to population increase. Birth Emigration Mortality Immigration Population size Trends in population size are a key focus of ecological research and its application to conservation biology. A decrease in size through time, for example, might signal declining health in a local population—a matter of practical concern when the population in question is a commercially harvested fish or an endangered species. Many factors affect population size: birth and immigration increase population size; mortality and emigration decrease population size.

PHYSICAL BASIS OF CLIMATE
48.1 Solar radiation, wind and ocean currents, and topography determine the distribution of major climatic zones on Earth. Climate: long-term average weather. Determined by: Solar radiation Global patterns of wind and ocean circulation Earth’s varying topography

Temperate broadleaf forest Savanna Northern coniferous forest Desert
Figure 40.7 30N Tropic of Cancer Equator Tropic of Capricorn 30S Figure 40.7 The distribution of major terrestrial biomes Tropical forest Temperate broadleaf forest Savanna Northern coniferous forest Desert Tundra Chaparral High mountains Temperate grassland Polar ice © 2016 Pearson Education, Inc.

Concept 40.4: Biotic and abiotic factors affect population density, dispersion, and demographics
Population ecology explores how biotic and abiotic factors influence density, distribution, and size of populations A population is a group of individuals of a single species living in the same general area Populations are described by their boundaries and size © 2016 Pearson Education, Inc. 46

Density: A Dynamic Perspective
In most cases, it is impractical or impossible to count all individuals in a population Sampling techniques can be used to estimate densities and total population sizes Population density can be estimated by extrapolation from small samples or an indicator of population size (for example, number of nests) © 2016 Pearson Education, Inc. 47

Density is the result of an interplay between processes that add individuals to a population and those that remove individuals Additions occur through birth and immigration, the influx of new individuals from other areas Removal of individuals occurs through death and emigration, the movement of individuals out of a population © 2016 Pearson Education, Inc. 48

Births Deaths Births and immigration add individuals to a population.
Figure 40.14 Births Deaths Births and immigration add individuals to a population. Deaths and emigration remove individuals from a population. Figure Population dynamics Immigration Emigration © 2016 Pearson Education, Inc.

Patterns of Dispersion
Environmental and social factors influence the spacing of individuals in a population The most common pattern of dispersion is clumped, in which individuals aggregate in patches A clumped dispersion may be influenced by resource availability and behavior © 2016 Pearson Education, Inc. 50

(a) Clumped (b) Uniform (c) Random Figure 40.15
Figure Patterns of dispersion within a population's geographic range (b) Uniform (c) Random © 2016 Pearson Education, Inc.

A uniform dispersion is one in which individuals are evenly distributed
In plants, it may occur as a result of the secretion of chemicals that inhibit the growth or germination of nearby individuals In animals, it may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals © 2016 Pearson Education, Inc. 52

In a random dispersion, the position of each individual is independent of other individuals
It occurs in the absence of strong attractions or repulsions among individuals It can also occur where key physical or chemical factors are relatively constant across the study area © 2016 Pearson Education, Inc. 53

Demographics Demography is the study of the vital statistics of a population and how they change over time Death rates and birth rates are of particular interest to demographers © 2016 Pearson Education, Inc. 55

Life Tables A life table is an age-specific summary of the survival pattern of a population It is best made by following the fate of a cohort, a group of individuals of the same age, from birth to death Life tables constructed for sexually reproducing species often ignore males because only females produce offspring © 2016 Pearson Education, Inc. 56

Survivorship Curves A survivorship curve is a graphic way of representing the data in a life table Survivorship curves plot the proportion or numbers of a cohort still alive at each age © 2016 Pearson Education, Inc. 58

Survivorship curves can be classified into three general types
Type I: high survivorship during early and middle life followed by a steep drop due to increase in death rates among older age groups Type II: survivorship declines linearly due to a constant death rate over the organism’s life span Type III: low survivorship due to high death rates for young age-groups and stable survivorship later in life due to a lower death rate for survivors © 2016 Pearson Education, Inc. 59

Number of survivors (log scale)
Figure 40.16 Number of survivors (log scale) 1,000 I 100 II 10 Figure Idealized survivorship curves: types I, II, and III III 1 50 100 Percentage of maximum life span © 2016 Pearson Education, Inc.

Reproductive Rates A reproductive table, or fertility schedule, is an age-specific summary of the reproductive rates in a population Reproductive output is typically measured as the average number of female offspring for each female in a given age-group © 2016 Pearson Education, Inc. 62

Concept 40.5: The exponential and logistic models describe the growth of populations
Unlimited growth occurs under ideal conditions; in nature, growth is limited by various factors Ecologists study growth in both idealized and realistic conditions © 2016 Pearson Education, Inc. 63

Changes in Population Size
Change in population size can be defined by the equation If immigration and emigration are ignored, the change in population size equals births minus deaths © 2016 Pearson Education, Inc. 64

The population growth rate can be expressed mathematically as
where N is the change in population size, t is the time interval, B is the number of births, and D is the number of deaths in the population during the time interval © 2016 Pearson Education, Inc. 65

The population growth equation can be revised
where R represents the difference between the number of births (B) and the number of deaths (D) © 2016 Pearson Education, Inc. 66

The per capita (per individual) change in population size (rt) represents the contribution that an average member of the population makes to the population size during the time interval t For example, for a population of 1,000 individuals that increases by 16 individuals per year, rt = 16/1,000 = 0.016 © 2016 Pearson Education, Inc. 67

For example, if rt = 0.016 and the population size is 500,
The formula R = rtN can be used to calculate how many individuals will be added to a population each year For example, if rt = and the population size is 500, R = rtN = × 500 = 8 per year © 2016 Pearson Education, Inc. 68

Change in population size can now be written as
© 2016 Pearson Education, Inc. 69

Population growth can also be expressed as a rate of change at each instant in time:
where dN/dt represents very small changes in population size over short (instantaneous) time intervals © 2016 Pearson Education, Inc. 70

Exponential Growth Exponential population growth is population increase under idealized conditions (food is abundant and all individuals reproduce at physiological capacity) Under these conditions, the population increases in size by a constant proportion at each instant in time © 2016 Pearson Education, Inc. 71

The equation of exponential population growth is
where r is the intrinsic rate of increase, the per capita rate at which a population increases in size at each instant in time © 2016 Pearson Education, Inc. 72

A population growing exponentially increases at a constant rate (r)
This results in a J-shaped growth curve A population with a higher intrinsic rate of increase will have a steeper growth curve © 2016 Pearson Education, Inc. 73

2,000 dN = 1.0N dt Population size (N) 1,500 dN = 0.5N dt 1,000 500 5
Figure 40.17 2,000 dN = 1.0N dt Population size (N) 1,500 dN = 0.5N dt 1,000 500 Figure Population growth predicted by the exponential model 5 10 15 Number of generations © 2016 Pearson Education, Inc.

The J-shaped curve of exponential growth characterizes populations in new environments or rebounding populations For example, the elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned © 2016 Pearson Education, Inc. 75

Elephant population size
Figure 40.18 8,000 Elephant population size 6,000 4,000 2,000 Figure Exponential growth in the African elephant population of Kruger National Park, South Africa Year © 2016 Pearson Education, Inc.

Carrying Capacity Exponential growth cannot be sustained for long in any population A more realistic population model limits growth by incorporating carrying capacity Carrying capacity (K) is the maximum population size the environment can support Carrying capacity varies with the abundance of limiting resources © 2016 Pearson Education, Inc. 77

As a population approaches carrying capacity, the per capita birth rate will decrease or the per capita death rate will increase Such changes in either (or both) of these rates cause the per capita growth rate (r) to drop © 2016 Pearson Education, Inc. 78

The Logistic Growth Model
In the logistic population growth model, the per capita rate of increase approaches zero as carrying capacity is reached The logistic model starts with the exponential model and adds an expression that reduces per capita rate of increase as N approaches K © 2016 Pearson Education, Inc. 79

Population growth is highest when the population size is at half the carrying capacity
At half carrying capacity the per capita rate of increase remains relatively high and there are more reproducing individuals than at low population size © 2016 Pearson Education, Inc. 80

The logistic model of population growth produces a sigmoid (S-shaped) curve

Exponential growth 2,000 dN = 1.0N dt Population size (N) 1,500
Figure 40.19 Exponential growth 2,000 dN = 1.0N dt Population size (N) 1,500 K = 1,500 Logistic growth dN (1,500 - N) = 1.0N dt 1,500 1,000 Population growth begins slowing here. Figure Population growth predicted by the logistic model 500 5 10 15 Number of generations © 2016 Pearson Education, Inc.

The Logistic Model and Real Populations
The growth of many laboratory populations, including paramecia, fits an S-shaped curve when resources are limited These organisms are grown in a constant environment lacking predators and competitors © 2016 Pearson Education, Inc. 84

Number of Paramecium/mL 1,000
Figure Number of Paramecium/mL 1,000 800 600 400 200 Figure How well do these populations fit the logistic growth model? (part 1: Paramecium) 5 10 15 Time (days) (a) A Paramecium population in the lab © 2016 Pearson Education, Inc.

The logistic model fits few real populations
Some populations overshoot K before settling down to a relatively stable density Some populations fluctuate greatly and make it difficult to define K © 2016 Pearson Education, Inc. 87

(b) A Daphnia (water flea) population in the lab
Figure Number of Daphnia/50 mL 180 150 120 90 60 30 Figure How well do these populations fit the logistic growth model? (part 2: Daphnia) 20 40 60 Time (days) (b) A Daphnia (water flea) population in the lab © 2016 Pearson Education, Inc.

Number of Paramecium/mL Number of Daphnia/50 mL 1,000 180
Figure 40.20 Number of Paramecium/mL Number of Daphnia/50 mL 1,000 180 150 800 120 600 90 400 60 200 30 5 10 15 20 40 60 Figure How well do these populations fit the logistic growth model? Time (days) Time (days) (a) A Paramecium population in the lab (b) A Daphnia (water flea) population in the lab © 2016 Pearson Education, Inc.

Concept 40.6: Population dynamics are influenced strongly by life history traits and population density An organism’s life history comprises the traits that affect its schedule of reproduction and survival The age at which reproduction begins How often the organism reproduces How many offspring are produced per reproductive episode © 2016 Pearson Education, Inc. 90

“Trade-offs” and Life Histories
Organisms have finite resources, which may lead to trade-offs between survival and reproduction Selective pressures influence the trade-off between the number and size of offspring Plants and animals whose young are likely to die often produce large numbers of small offspring © 2016 Pearson Education, Inc. 91

Some plants and animals produce a moderate number of large offspring
For these species, extra investment by the parent greatly increases the offspring’s chance of survival © 2016 Pearson Education, Inc. 92

(a) Dandelions release a large number of tiny fruits.
Figure 40.21 (a) Dandelions release a large number of tiny fruits. Figure Variation in the number and size of seeds in plants (b) The Brazil nut tree (above), produces a moderate number of large seeds in pods (left). © 2016 Pearson Education, Inc.

K-selection, or density-dependent selection, operates in populations experiencing competitive conditions at population densities close to carrying capacity r-selection, or density-independent selection, selects for life history traits that maximize reproduction at low population density © 2016 Pearson Education, Inc. 94

Population Change and Population Density
In density-independent populations, birth rate and death rate do not change with population density In density-dependent populations, birth rates fall and death rates rise with population density © 2016 Pearson Education, Inc. 95

population grows until the density reaches Q.
Figure 40.22 When the density is low, there are more births than deaths. Hence, the population grows until the density reaches Q. When the density is high, there are more deaths than births. Hence, the population shrinks until the density reaches Q. Birth or death rate per capita Equilibrium density (Q) Density-independent death rate Figure Determining equilibrium for population density Density-dependent birth rate Population density © 2016 Pearson Education, Inc.

Mechanisms of Density-Dependent Population Regulation
Density-dependent birth and death rates are an example of negative feedback that regulates population growth Population growth declines at high density due to factors such as competition for resources, predation, disease, toxic wastes, territoriality, and intrinsic factors © 2016 Pearson Education, Inc. 97

Disease transmission rates may increase with increasing population density

Territoriality can limit population density when space becomes a limited resource

Stability and Fluctuation
Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time Both weather and predator population can affect population size over time For example, collapses in the moose population on Isle Royale coincided with a peak in the wolf population during one time period and with harsh winter conditions in another © 2016 Pearson Education, Inc. 105

Population size (N) dN = rN dt Number of generations Figure 40.UN02
Figure 40.UN02 Summary of key concepts: exponential population growth equation Number of generations © 2016 Pearson Education, Inc.

50 2,500 Wolves Moose Number of wolves Number of moose 40 2,000 30
Figure 40.24 50 2,500 Wolves Moose Number of wolves Number of moose 40 2,000 30 1,500 20 1,000 10 500 Figure Fluctuations in moose and wolf populations on Isle Royale, 1959–2011 1955 1965 1975 1985 1995 2005 Year © 2016 Pearson Education, Inc.

Immigration, Emigration, and Metapopulations
Metapopulations are groups of populations linked by immigration and emigration Local populations within a metapopulation occupy patches of suitable habitat surrounded by unsuitable habitat Populations can be replaced in patches after extinction or established in new unoccupied habitats through migration © 2016 Pearson Education, Inc. 109

Åland Islands EUROPE Occupied patch Unoccupied patch 5 km Figure 40.25
Figure The Glanville fritillary: a metapopulation Occupied patch 5 km Unoccupied patch © 2016 Pearson Education, Inc.

Competition for resources Predation Disease
Figure 40.23 Competition for resources Predation Disease 5 mm Figure Exploring mechanisms of density-dependent regulation Toxic wastes Territoriality Intrinsic factors © 2016 Pearson Education, Inc.

40 Population Ecology and the Distribution of Organisms.

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40 Population Ecology and the Distribution of Organisms.

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