Basic Characteristics of Ecosystems Sustained life on Earth is a characteristic of ecosystems, not of individual organisms or populations Structure (two major parts) –Living (Ecological Communities) –Non-living Processes (two basic kinds) –Cycling of chemical elements –Flow of energy Change –Predictable – succession –Unpredictable change
Ecological Communities and Food Chains Ecological Communities are defined in two ways: –1. A set of interacting species that occur in the same place defined by the way they derive energy: Food chains, food webs, trophic levels (autotrophs) –2. A set of all species found in one area. EG. Zoo animals
Food Chains and Food Webs A Terrestrial Food Chain –Four trophic levels: –Example: Autotrophs Herbivores Carnivores Decomposers –People are omnivores
Food Chains and Food Webs Continued… An Oceanic Food Chain –Involve more species and tend to have more tropic levels. See figure 6.6 The Food Web of the Harp Seal –Shows how complex a real-life food web truly is.
The Community Effect Species interact directly (symbiosis & competition) and indirectly Community-level interactions –Indirect interactions. Keystone species –Have large effects on its community or ecosystem –Its removal changes the basic nature of the community –See Sea Otter example figure 6.8. Sea otters influence the abundance of sea urchins Holistic View –An ecological community is more than the sum of its parts.
How Do You Know When You Have Found an Ecosystem? Vary greatly in structural complexity. The watershed is a common, practical delineation. What is a watershed? Common to all ecosystems is energy flow and cycling of chemical elements.
Ecosystem Management Ecosystem management is the key to conservation of life on Earth, but it is difficult to know the exact limits of the system and is equally difficult to know all of the interactions that take place within it. If ecosystems cease to function we must supplement with our own actions. Must consider chemical cycling, energy flow, community-level interactions, and natural changes.
Biological Diversity and Biological Evolution Biological Diversity (biodiversity) –The variety of life-forms commonly expressed as the number of species in an area Biological Evolution –The change in inherited characteristics of a population from generation to generation –One of the features that distinguishes life from everything else in the universe
Four Processes that Lead to Evolution Mutation Natural Selection Migration Genetic Shift
Mutation A chemical change in a DNA molecule Affects the expressed characteristics when cells or individual organisms reproduce
Natural Selection 4 Characteristics: –Genetic Variability –Environmental Variability –Differential Reproduction –Environmental Influence Species: –a group of individuals that reproduce with each other and produce fertile offspring
Peppered Moth Example Originally White Now more black than white Causes –Industrial Pollution Soot covered trees –Industrial Melanism http://www.echalk.co.uk/Science/science.htm
Migration Two new species evolve from an original species due to isolation Ex: land bridge
Genetic Drift Changes in the frequency of a gene in a population due to chance Can be a problem for rare or endangered species
Basic Concepts of Biological Diversity Genetic Diversity Habitat Diversity Species Diversity Species Richness Species Evenness Species Dominance
Species A group of organisms that can reproduce and produce fertile offspring. Ubiquitous species –Worldwide distribution –Overly common in an area Endemic species –Organisms unique to one place only. Indicator species –The first native organisms in an ecosystem, to show the effects of environmental problems.
The Number of Species of Life on Earth No one knows the exact number About 1.4 million species have been identified and named Insects and plants make up moth of these species Number will increase
The Competitive Exclusion Principles 2 species that have exactly the same requirements cannot coexist in exactly the same habitat Ex) introduction of the gray squirrel into Great Britain
Professions and Places: The Ecological Niche and the Habitat Habitat: where a species lives Ecological Niche: a species profession The reason more species do not die out from competition is that they have developed a niche, and thus avoid competition
What is the effect of each species on the other?
Species Engage in 3 Basic Interactions 1. Competition 2. Symbiosis 3. Predation-Parasitism Each affect evolution, persistence of a species and the overall diversity of life Organisms have evolved together and therefore adjusted to one another Human interventions upset these adjustments
Symbiosis The relationship between two organisms that is beneficial to both and enhances each organisms chances of persisting –Mutualism, parasitism, commensalism Obligate symbionts: –a symbiotic relationship between two organisms in which neither by themselves can exist without the other –Ex) stomach of a reindeer
Why Were Introductions of New Species into Europe So Popular Long Ago? Biogeography: –The large scale geographic pattern in the distribution of species, and the causes and history of this distribution
Wallaces Realms: Biotic Provinces Realm: –Major biogeographic regions of Earth that are based upon fundamental features of the plants and animals found in those regions Taxa: –Categories that identify groups of living organisms based upon evolutionary relationships or similarity of characteristics (ex: species, families, orders) Biotic Provinces: –A geographical region (realm) inhabited by a characteristic set of taxa, bounded by barriers that prevent the spread of those distinctive kinds of life to other regions.
The main biogeographic realms for animals are based on genetic factors.
The major vegetation realms are also based on genetic factors
Biomes A biome is a kind of ecosystem. Similar environments provide similar opportunities for life and similar constraints. –Rainforest –Grasslands –Desserts
Climate is the most important factor in determining the type of biome that will be found in an area
The process by which species evolve in different places of times and, although they have different genetic heritages, develop similar external forms and structures as a result of adaptation to similar environments –Ex) shapes of sharks Convergent Evolution
Divergent Evolution Organisms with the same ancestral genetic heritage migrate to different habitats and evolve into species with different external forms and structures, but continue to use the same type of habitats –Ex) Ostrich
Island Biogeography Theory of Island Biogeography –Islands have fewer species than continents –The smaller the island, the fewer the species Adaptive Radiation: –The process that occurs when a species enters a new habitat that has unoccupied niches and evolves into a group of new species, each adapted to one of these niches. Ecological Island: –An area that is biologically isolated so that a species occurring within the area rarely mixes with any other population of the same species