Communities

define community

all the populations of plants and animals living and interacting within an ecosystem

define ecological niche

the role or function a species plays in its environment

identify the different trophic levels in food webs

1. autotrophs (plants/phytoplankton)

2. heterotrophs (herbivores, carnivores, omnivores)

3. detritivores 

identify the efficiency of energy transfer at each trophic level

only 10% of energy is passed between trophic levels; 90% is lost as heat 

explain the effect of biodiversity/complexity on community stability

Because they have multiple species that can fulfill similar roles, providing resilience when one species declines

explain how genetic diversity affects community stability

increases the chance that some individuals in a population can adapt to environmental changes

explain how species redundancy affects community stability

it provides a “deep bench”— if one species is lost, another can fill its role, maintaining ecosystem function

Define keystone species

has a disproportionately large effect on the community relative to its biomass. removing it can cause major changes to diversity and structure

explain the role of a keystone predator

controls prey populations, preventing competitive exclusion and maintaining biodiversity

ex. sea stars prey on mussels, removing sea stars led to mussels outcompeting other species

explain the role of a keystone modifier

physically alters the environment, creating habitats and increasing productivity 

ex. kangaroo rats and prairie dogs maintain desert and prairie ecosystems 

explain what happens in a trophic cascade

when changes at one trophic level (e.g., predator loss) ripple through the ecosystem, altering abundance and productivity of multiple levels.

Explain how increased biodiversity can reduce trophic cascades

Higher biodiversity spreads ecological roles across more species, so the loss of one predator or prey has less dramatic ripple effects

Predator strategies

Sit-and-wait predators- ambush prey

Active hunter- pursue prey

define search image

the mental image predators form of preferred prey after repeated successful encounters, helps them locate prey more efficiently

Explain what happens in predator-prey cycles

prey increase first, then predators follow. The predator population lags behind. Over time, both adapt to each other’s strategies 

What is mesopredator release

the removal or decline of an apex predator will allow lesser predators (mesopredators) to increase dramatically

why is mesopredator release a problem

Because mesopredators can overexploit prey species, leading to biodiversity loss and ecosystem imbalance.

Instraspecific vs. Interspecific

• Intraspecific: competition within the same species (e.g., for mates or territory).

• Interspecific: competition between different species for shared resources

what is competitive exclusion

when one species consistently outcompetes another for the same resources, leading to the exclusion (local extinction) of the weaker competitor

describe an example of predator-mediated competition

Pine martens prey on gray squirrels, allowing red squirrels (normally outcompeted) to survive better

Explain species mutualisms in communites 

an interaction where both species benefit 

• clownfish and sea anemones

• cattle egrets and grazing animals

• sharks and remoras