Ecology: Community Structure, Succession, and Food Webs

Community Zonation

Species composition of the community changes across the landscape.

Ecotone

A boundary caused by a sharp change in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species.

Ecotone Present

Sharp changes in distribution of species as one community leaves and another enters.

Line-transect surveys

Can be used to document ecotones.

Interdependent Community

Species depend on each other to exist (superorganisms).

Independent Community

Species do not depend on each other to exist.

Abundance

Absolute: number of individuals in each species that are counted.

Relative Abundance

Proportion of individuals in a community represented by each species.

Rank-Abundance Curve

Shows relative abundance of each species in a community in rank order, from most to least abundant.

Species Richness

Number of species in a community.

Species Evenness

Comparison of the relative abundance of each species in a community.

Species Diversity

More species + greater evenness = higher species diversity.

Simpson's Index

A measure of diversity that accounts for both richness and evenness.

Shannon's Index

A measure of the uncertainty in predicting the species of a randomly chosen individual from a dataset.

Productivity

Biomass of producers or consumers generated over time.

Keystone Species

Substantially affects the structure of communities even when individuals of that species may not be particularly numerous.

Food Chain

Linear representation of how species in community consume each other + how they transfer energy, nutrients from one group to another.

Food Web

Complex and realistic representations of how species in community feed on each other.

Trophic Levels

Levels in a food chain or food web of an ecosystem.

Top-down control

Abundance in trophic group is determined by predators at the top of the food web.

Bottom-Up Control

Abundance of trophic groups in community determined by amount of energy available from the producers in that community.

Succession

Changes in a community's species composition over time.

Pioneer Species

Earliest species to arrive in a new habitat.

Climax Community

Final seral stage of succession.

Chronosequencing

Creates model of the sequence of communities that exist over time in a given location.

Primary Succession

Initially devoid of plants and organic soil (e.g., sand dunes, lava flows, bare rock).

Secondary Succession

Habitat contains no plants but does have organic soil.

Facilitation

The presence of one species increases the probability that a second species can establish.

Inhibition

One species decreases the probability that a second species will establish.

Community Stability

Ability of a community to maintain a particular species composition.

Community Resistance

How much a community changes when acted upon by a disturbance.

Community Resilience

Ability of a community to return to its original state after being disturbed.

Alternative Stable State

New community structure.

Net Primary Productivity (NPP)

Rate at which energy is assimilated (taken in) by producers and converted into producer biomass.

NPP Formula

NPP = GPP - respiration.

Green Food Web

How producers obtain energy from photosynthesis (or chemosynthesis) and how this energy moves up the food web when producers are consumed.

Brown Food Web

How scavengers, detritivores, decomposers obtain energy from dead organic matter and how this energy moves up the food web when they are consumed.

Respired Energy

Portion of assimilated energy used for respiration.

Net Second Productivity

Rate of biomass accumulation of consumers.

Nutrients for Producers

Nitrogen and Phosphorus are needed in greatest amounts to build producer biomass.

NPP Limitation

NPP is limited by nitrogen and phosphorus.

Trophic Pyramid

Chart of stacked layers representing relative amount of energy or biomass in each trophic level.

Consumption Efficiency

Percentage of energy or biomass in a trophic level consumed by the next higher level.

Assimilation Efficiency

Percentage of consumed energy assimilated by consumer.

Net Production Efficiency

Percentage of assimilated energy used for growth and reproduction.

Ecological Efficiency

Percentage of net production from one trophic level compared to the next lower trophic level.

Energy Residence Time

Length of time energy spends in a given trophic level.

Biomass Residence Time

Length of time biomass spends in a given trophic level.

Ecological Stoichiometry

The study of the balance of nutrients in ecological interactions.

Legacy Effect

Historical processes that have long-lasting influence on current ecology of an area.

Local Diversity (Alpha diversity)

Number of species in relatively small area of homogeneous habitat.

Regional Diversity (Gamma diversity)

Number of species in all the habitats that comprise a large geographic area.

Beta Diversity

Number of species differs between two local habitats.

Regional Species Pool

Collection of species within a region.

Species-Area Curve

Graphical relationship in which increases in area (A) are associated with increases in the number of species (S).

Fragmentation Effects

1. Total number of habitats decreases; 2. Number of habitat patches increases; 3. Average patch size decreases; 4. Amount of edge habitat increases; 5. Patch isolation increases.

Corridors

Important for organisms needing continuous connection to move between fragments.

Stepping Stones

Small intervening patches that dispersing organisms can use to move between large favorable habitats.

Equilibrium Theory of Island Biogeography

The number of species on an island reflects a balance between the colonization of new species and the extinction of existing species.

Instrumental Value Biodiversity

Economic values that species can provide.

Intrinsic Value of Biodiversity

Do not provide economic benefits; religious, moral, ethical obligation to preserve the world's species.

Species Definitions

1. Abundant: not likely to become threatened in the future; 2. Threatened: populations face a high risk of extinction in the future; 3. Extinct: species known to be alive in 1500, but no individuals remain alive today.

Declines in Genetic Diversity

Caused by decreasing population sizes, inbreeding depression, and bottleneck effect.

Svalbard Global Seed Vault

Protects genetic diversity of plant varieties.

Introduced Species

Can cause a loss in biodiversity.

Biodiversity Maintenance Strategies

Long term: stabilize size of human population; Short Term: reduce sources of mortality, low reproduction caused by humans.