Community Ecology Flashcards
What is an ecological community
A group of species that occur together in space and/or time and compete for the same limiting resource
What is meant by a “limiting resource”
A resource that species consume and deplete, making it scarce and leading to competition
Why are ecological communities considered fundamentally competitive
Because species in a community rely on shared, limited resources and must compete to survive
Why doesn’t one species always outcompete the others
Mechanisms like niche differentiation and environmental variation allow coexistence, also, the competitive exclusion principle provides conditions under which coexistence is not possible
What is Gause’s principle of competitive exclusion
Two species competing for a single limiting resource cannot coexist if all other ecological factors are constant
Describe Connell’s barnacle experiment
Chthamalus is excluded from the lower shore by Balanus (stronger competitor), but persists in the upper shore due to greater desiccation tolerance
What is character displacement in Fenchel’s snails
When coexisting, H. ulvae shifts feeding patterns and grows larger than H. ventrosa to reduce competition
What are diatoms and what limits their growth in Tilman’s experiments
Photosynthetic planktonic organisms limited by silica. Silica availability determines growth rates and competitive outcomes
What is the R* theory
The species with the lowest R* (resource level at which it can maintain equilibrium) is the best competitor for that resource
What is coexistence in ecology
When two species persist together long-term, often due to niche differentiation or environmental variation
What does the Lotka-Volterra model describe
How two species compete based on intra- and interspecific competition and predicts possible outcomes including stable coexistence
What is the condition for coexistence in Lotka-Volterra model
Coexistence occurs if:
K₁ > K₂α₁₂ and K₂ > K₁α₂₁
(i.e. interspecific competition is weaker than intraspecific)
What is an ecological niche
The specific way a species uses resources and interacts with its environment, helping reduce interspecific competition
How did MacArthur’s warbler study support the niche concept
Warblers used different parts of the same tree, reducing direct competition and allowing coexistence
What happens when Cape May warblers increase in number
Other species feeding in the tops of trees suffer most due to competition over shared food resources
What is the effect of strong density-dependence within species
High intraspecific competition when population is dense slows growth, low density boosts growth - stabilises coexistence
Why do species evolve different niches
Life history trade-offs and long-term competition push species to specialize in what they’re best at
What is a Darwinian demon
A hypothetical species with perfect traits for all functions (e.g. fast growth and strong defence) - doesn’t exist due to resource trade-offs
What are pioneer vs shade-tolerant tree strategies
Pioneer (e.g. Birch): fast-growing, short-lived, can’t regenerate in shade
Shade-tolerator (e.g. Beech): slow-growing, long-lived, regenerates in shade
How do tree death dynamics support coexistence in forests
Shade-tolerator dies → light gap → pioneers grow
Pioneer dies → gap filled by shade-tolerator saplings → creates a dynamic balance enabling coexistence
Why does heterogeneity promote coexistence
Spatial/temporal variation (e.g. light, soil) provides different niches for different species, reducing direct competition
How does adaptive radiation support coexistence
Closely related species evolve different morphologies and behaviours to exploit different niches and avoid competition
