Leader: Kirsten Karkow
Course: Biol 211 - Wilsey
Date: 4/18/2012
Worksheet 31
Supplemental Instruction
Iowa State University
Community ecology focuses on interactions between species. These are known as
interspecific interactions. (Interactions between individuals of the same species are termed
intraspecific interactions.)
Define the following terms:
Symbiosis
Coevolution
Niche
Competitive
Exclusion Principle
Fundamental Niche
Realized Niche
Situation in which 2+ species live in direct/intimate contact with one
another. Will be interdependent. Often co-evolve.
When the evolution of one species influences the evolution of another
and vice versa. Occurs when species have some sort of dependency.
A species’ ecological role – where, what, and when it eats.
Two species cannot occupy the exact same niche in a sustainable
manner. One will eventually be stifled by the other.
Where an organism would live if no competitor was present.
Where an organism does live (due to the presence of competition).
Describe how the following can help species with similar niches occupy the same area:
Resource Partitioning – different species that eat the same food will eat at different
times, places, or parts. Results in differentiation of niches.
Keystone Predators – have a vital role in preying on competitive species. Prevent
competitive exclusion.
Disturbances – help maintain communities by knocking back the most popular
(competitive) species. Prevent competitive exclusion.
Spatial Variation – differences in resources maintain differences within that community.
Identify the following interspecific interactions. Indicate which ones are forms of symbioses:
Competition
Predation
Herbivory
Parasitism (S)
Mutualism (S)
Commensalism (S)
(-/-) when 2+ species require the same limited resource. Can be
intraspecific, interspecific, or asymmetrical.
(+/-) when one species (the predator) kills and eats the other.
(+/- or 0) when one species eats a plant or algal species.
(+/-) parasite derives nourishment from the host, harming it.
(+/+) interaction that benefits both species. Ex. – plants & pollinators,
mycorrhizal fungi, lichens, legumes & N-fixing bacteria.
(+/0) Interaction that benefits one species but doesn’t affect the other.
Ex. – buffalo and cowbird.
Supplemental Instruction
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Describe the following adaptations in prey:
Cryptic Coloration
Warning Coloration
Batesian Mimicry
Mullerian Mimicry
Camouflage. A passive defense. Low cost.
Used by animals that synthesize toxins. An active defense. High cost.
When a harmless species mimics a harmful one.
When harmful species mimic each other. Predators will become
wary of their appearance even faster.
Why can the introduction of an exotic species lead to dramatic changes at the community
level?
Exotic species often grow exponentially due to a lack of environmental resistance in new
locations. (Often have few to no predators or parasites. Competitors may be weaker since they
have not co-evolved over time. Etc.) The overabundance of these organisms may cause other
species to die out.
Describe the following types of ecological succession:
1. Primary – communities establish in a newly formed (uninhabited) habitat.
Step 1. Lichens and mosses produce organic matter (soil)
Step 2. Nitrogen-fixing species add N to the soil and produce more soil
Step 3. More species are introduced.
2. Secondary – communities establish in a previously occupied habitat.
Step 1. Annual plants arise
Step 2. Perennial plants arise.