Ch 17 - Species Interactions + Community Structure
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54 Terms
What is a food web?
A network of feeding relationships in a community
What do food webs show?
How energy and nutrients flow through ecosystems
Why are food webs important?
They represent key interactions shaping communities
Why are food webs complex?
Species interact with many others through multiple pathways oai_citation:2‡Biol_341_Ch17.pdf
What is a strong interaction?
An interaction where a species has a large effect on community structure oai_citation:3‡Biol_341_Ch17.pdf
What determines a strong interaction?
The degree of influence on community structure oai_citation:4‡Biol_341_Ch17.pdf
What is a direct interaction?
Interaction between two species without intermediaries oai_citation:5‡Biol_341_Ch17.pdf
What is an indirect interaction?
Interaction between species mediated through a third species oai_citation:6‡Biol_341_Ch17.pdf
What is a trophic cascade?
When predators indirectly affect lower trophic levels oai_citation:7‡Biol_341_Ch17.pdf
What happens in a trophic cascade when predators are removed?
Prey increases, producers decrease
What is apparent competition?
Two species negatively affect each other through a shared predator oai_citation:8‡Biol_341_Ch17.pdf
Why is it called “apparent” competition?
The species do not directly compete but appear to
Give an example of apparent competition
An invasive plant increases herbivores that also eat native plants
What happens when a shared predator increases?
Both prey species may decline
What is indirect commensalism?
One species benefits indirectly from another via a third species
How do indirect interactions affect communities?
They can strongly shape species abundance and diversity
What happens as food web diversity increases?
The proportion of predators increases oai_citation:9‡Biol_341_Ch17.pdf
How does predator presence affect diversity?
It can increase diversity by limiting dominant prey
When can predation reduce diversity?
If it becomes too strong and destabilizes populations
What is a keystone species?
A species with large effects despite low abundance oai_citation:10‡Biol_341_Ch17.pdf
What is a foundation species?
A species with large effects due to high biomass oai_citation:11‡Biol_341_Ch17.pdf
What is a dominant species?
A species with high biomass that strongly influences the community
How do keystone species differ from dominant species?
Keystone = low biomass, dominant = high biomass
What happens when a keystone species is removed?
Community structure collapses or changes drastically
Example of keystone species
Sea stars controlling intertidal diversity oai_citation:12‡Biol_341_Ch17.pdf
What happened when sea stars were removed?
Diversity dropped and one species dominated
Why are sea stars keystone species?
They prevent competitive exclusion
What do snails prefer to eat?
Small, fast-growing (ephemeral) algae oai_citation:13‡Biol_341_Ch17.pdf
What happens without snails?
Tough algae (Chondrus) are outcompeted
How do snails affect algal communities?
They control species composition through grazing
What role do predatory fish play in ecosystems?
They reduce prey populations and indirectly affect producers oai_citation:14‡Biol_341_Ch17.pdf
What happens when predator fish are reduced?
Prey increase, leading to increased pressure on producers
Example: what happens to algae when predators are low?
Algae decrease due to increased herbivory
What is a trophic level?
A position in the food chain (producer, herbivore, carnivore)
What is a top predator?
An organism at the highest trophic level
How do top predators influence ecosystems?
They regulate lower trophic levels
What is a cleaner fish mutualism?
Fish remove parasites from other fish oai_citation:15‡Biol_341_Ch17.pdf
Why are cleaner fish considered keystone species?
They strongly affect species diversity
What happens when cleaner fish are removed?
Fish diversity decreases significantly
What happens when cleaner fish are added?
Fish diversity increases
What is a seed dispersal mutualist?
An organism that spreads seeds to new locations oai_citation:16‡Biol_341_Ch17.pdf
How do ants act as keystone species?
They disperse seeds and affect plant recruitment
What happens when native ants are replaced by invasive ants?
Seed dispersal decreases and plant recruitment drops
Why are invasive ants harmful?
They disrupt mutualisms
What is bioaccumulation?
Build-up of toxins within an organism over time oai_citation:17‡Biol_341_Ch17.pdf
What is biomagnification?
Increasing concentration of toxins at higher trophic levels oai_citation:18‡Biol_341_Ch17.pdf
Why does biomagnification occur?
Predators consume many contaminated prey
What is an example of biomagnification?
DDT accumulating in top predators like birds
What happens to toxin levels at higher trophic levels?
They increase dramatically
Why are top predators most affected by toxins?
They accumulate toxins from all lower levels
What is the overall role of food webs in ecology?
They determine energy flow and species interactions
What is the key takeaway about community structure?
A few species and interactions can control entire ecosystems
What is the relationship between interaction strength and ecosystem stability?
Strong interactions can stabilize or destabilize communities
What is the main takeaway of Chapter 17?
Community structure is shaped by food webs, indirect interactions, and keystone species