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AP Bio-Forbes-Ecology 3: Community Interactions
Transcript of AP Bio-Forbes-Ecology 3: Community Interactions
Interactions Organism Population Community Ecosystem Biome Biosphere Where Are We? Ecology is the study of organism interactions with each other and the enviornment.
Ecological processes occur at multiple levels of organization on Earth.
Each level of organization emerges from the processes of the level below it Behavior is an Organism-Level phenomenon. Big Questions: Make Sure You Can How are communities structured?
How do the interactions of species in a community lead to emergent properties? Describe and compare all of the community interactions discussed in this presentation and provide multiple examples of each.
Explain the relationship between community diversity and stability.
Quantitatively demonstrate the diversity of a community.
Explain the interactions in a community that contribute to its trophic structure.
Explain why community diversity is maximized when disturbance is present at an intermediate level.
Explain the processes of primary and secondary seccession.
Explain the effects of all of the biogeographical factors discussed in this presentation on community structure. Competition Predation Herbivory Symbiosis Facilitation Characterizing Communities Diversity Trophic Structure Effects on Diversity Disturbance Biogeographic Factors A contest between individuals for shared resources.
A -/- interaction One species (the predator) kills and eats the other species (the prey).
A +/- interaction.
Predation drives evolution because it provides a strong selective pressure on prey populations. All of the populations in a contiguous area.
Properties emerge from interactions in the community. One species (the herbivore) eats part of a producer (plant or algae)
A +/- interaction
Producers have evolved many adaptions to control herbivory. Two or more species live in close contact with eachother.
Three major types of symbiotic interactions. Species have positive effects on other species in the community without being in a symbiotic relationship.
A +/+ or 0/+ interaction. Between species (interspecific) or within a species (conspecific). Niche: All of an organism's interactions in its environment Competition limits an organism's niche.
Fundamental niche: maximum possible niche.
Realized niche: actual niche. Removal of Balanus barnacles demonstrates the difference between the fundamental and realized niche of Chthamalus barnacle Effects of Competition Competitive Exclusion Resource Partitioning When two species have overlapping niches, one will outcompete the other. Competitive exclusion of Asterionella by Synedra (2 diatom species) for silica in a laboratory culture. Competition drives species with overlapping niches to adapt to non-overlapping resource pools. Resource partitioning among Anole lizards in the Carribean tropics. Character Displacement Competing populations are more divergent in adaptive characteristics than non-competing populations of the same species. Character Displacement of beak depth in 2 species of Galapagos Finch Effects of Predation Coloration Mimicry Cryptic: Camouflage or other coloration that confuses predators Aposematic: Warning coloration, advertising a threat to predators Mullerian: Two or more harmful species with common predators mimic each other. Batesian: A harmless species mimics a harmful species. Effect of trichome number on herbivory in pea plants. Mutualism Parasitism Commensalism a +/+ interaction a +/- interaction a +/0 interaction Sea urchin/crab Clownfish/anemone Wasp/blowfly larva Brood parasitism Mosquito/mammal African buffalo/Egret Nesting bird/tree Everybody wins! The most common symbiosis Is commensalism a "myth?" Wasp/caterpillar Easily one of the grossest things I show you all year Lichens are classic facillitators. Juncus is a facilitator in North American salt marsh ecosystems Beavers are "ecosystem engineers", who create entire novel communities through their actions in an ecosystem. The variety of different organisms that comprise the community.
Correlates to the stability of the community (more diverse = more tolerant of disturbances).
Can be understood in terms of:
Species richness: the number of different species.
Relative abundance: the proportion of each species to the total in the community Two hypothetical communities. Which one is more diverse, and why? The relationship between soild pH and microbial diversity in North American communities.
Diversity is frequently measured in terms of Shannon Diversity H' = Shannon Diversity
s = species richness
p = relative abundance of each species (i) The feeding relationships present in a community. What eats what? Food Chain Food Web One sequential series of trophic relationships in a community. Many, interconnected trophic relationships in a community. Keystone Species Species that have a large effect on the structure of the community. Evidence supporting the hypothesis that the Pisaster seastar is a keystone species. Evidence supporting the hypothesis that sea otters are a keystone species. Trophic Limits Why are food chains limited in length? Energetic Hypothesis:
Only enough energy to support a certain number of links.
Rule of 10%-only 10% of energy is transferred between trophic levels
producer level can only support 10% of biomass-total dry mass of organisms in a trophic level-standing crop
Longer food chains found in habitats with high photosynthetic production production Dynamic Stability Hypothesis:
The longer a food chain, the less stable it is.
Population fluctuations at lower trophic levels severely impact the higher trophic levels-occurs most often in unstable environments.
Can lead to extinction of top predators Leaf litter experiment in tree hole community
As energy input decreases, trophic links decrease. Any event that alters community structure by removing organisms or changing resource availability. The "Intermediate Disturbance Hypothesis": Diversity will be highest in ecosystems that experience intermediate levels of disturbance Example:
Invertebrate taxonomic diversity is highest in Australain wetland ecosystems that experience intermediate amounts of flooding. Human activities increase disturbance in most communities.
Pre-trawling community in Gulf of Mexico (top)
Post-trawling community (bottom) Succession The sequential changes that occur in a community following a disturbance. Primary Secondary Succession on previously uninhabited land-no soil Succession on previously inhabited land Primary succession in Glacier Bay, Alaska Secondary succession following fire. Pioneer Organisms Climax Community Island Effects Area Effects Evapotranspiration The larger the ecosystem, the more species tend to be present.
Why? The greater the rate of evaporation and transpiration, the more species tend to be present.
Why? An "island" is any isolated ecosystem (including actual islands).
Several factors contribute to the number of species in an island ecosystem. Data demonstrating the relationship between island size and plant species diversity in the Galapagos Islands. Immigration/Extinction rate, Island Size, and the distance of the "island" from the "mainland" all factor in determining the equilibrium number of species found in an island ecosystem. An aphid extruding sap Though really, we have nothing on nature...