Community Ecology Flashcards
Community def
An assemblage of individuals of different species in a certain area at a certain time
How do ecologists distinguish between communities
-composition: species composition (which species), species richness (how many), diversity (number and evenness)
-structure: trophic structure (food web), plant growth forms
Vertical structure of communities
Heights of canopies in which species live
Communities have distinct or gradual boundaries called….
Ectotones
Gradual
Gradual boundaries
Usually follow gradients
-latitude
-altitude
-humidity
-salinity
-exposure
Eco tones
Rather sharp transition from one community to a different, adjacent one.
Sharp changes in environmental condition Over short distances leading to a major change in the composition of species
Species richness is greater where?
I’m the ecotone
Interdependent vs independent views of communities
Interdependent or organismic view: highly organized systems with tight associations among species
Approach to study: classification
Independent or individualistic view: haphazard collection of individuals with little integration together because they have similar environmental requirements
Approach to study: dynamics, functional organization
Independent is better approach
What can be used to measure species diversity and richness
Simpsons index
Shannon-wiener index
Rank abundance curves
-greater evenness seen by smaller slope
-more species richness seen by longer line
What has happened to plant diversity since long term fertilization?
-diversity has declined
Natural patterns of productivity and species richness
-U shaped
-negative
-none
-positive
-hump shaped (common)
Keystone species
Species that, despite low biomass, exert strong effects on the structure of the communities they inhabit
A species who’s removal produces a significant effect on other species
Effects spread through food Web
Pisaster keystone species example
Starfish are keystone predators on shores
Pisaster clams in absence of star fish take over the shore and decrease biodiversity
More starfish=more diversity
Top down and bottom up effects of food webs
Reduction of a producer, will result in less primary consumers, then less secondary consumers and then less tertiary consumers.
Reduction in tertiary consumer, will result in more secondary consumers, will result in less primary consumers, and more producers
Stability
Ability of community to maintain structure
Resilience
Measures as the time it takes after disturbances for a community to return to original state
Resistance
Amount of change in a community after disturbances (more change=lower resistance)
Low disturbance means what generally?
1 species overt takes the others and species richness decreases
Is there more or less stability with more species
More
Species richness
Number of species in a community
Species evenness
A comparison of the relative abundance of each species in a community
Intermediate disturbance hypothesis
More species are present in a community that experiences occasional disturbances than in a community that experiences frequent or rare disturbances
Direct effect
Indirect effect
When two species interact without involving other species
When two species interact and invoke one or more intermediate species
Trophic cascade
Indirect effects in a community that are initiated by a predator
Density-mediated indirect effect
An indirect effect caused by changes in the denature of an intermediate species
Trait-mediated indirect effects
An indirect effect caused by changes in the transits of an intermediate species
-when a predator causes its prey to change its feeding behaviour which in turn alters the amount of food consumed by the prey
Bottom up control
Top down control
When the abundance of trophic groups in nature are determined by the amount of energy available from the producers in a community
When the abundance of trophic groups is determined by the existence of predators at the top of the food web
