Chapter 54 Outline
Community Ecology
Professor: Mark D. Graves
Updated 201901

This chapter address the question:
o :_____________________________________
Communities in Motion

Define:
o Community: is an assemblage of populations of various species living close enough for
potential interaction
Community interactions are classified by whether they help, harm, or have no effect on the species
involved




Define:
o Interspecific interactions: A relationship between individuals of two or more species in a
community.
o 6 interactions:
 : competition
 : predation
 : herbivory
 : parasitism
 : mutualism
 : commensalism
o Competition: A -/- interaction that occurs when individuals of different species compete
for a resource that limits the survival and reproduction of each species.
 Example: Weeds growing in a garden compete with garden plants for soil
nutrients and water.
o Competitive exclusion: The concept that when populations of two similar species
compete for the same limited resources, one population will use the resources more
efficiently and have a reproductive advantage that will eventually lead to the elimination
of the other population.
o Ecological niche: The sum of a species’ use of the biotic and abiotic resources in its
environment.
Can two species coexist permanently if their niches are identical?
o : Two species cannot coexist permanently in a community if their niches are identical.
o If not identical? : However, ecologically similar species can coexist in a community if
one or more significant differences in their niches arise through time.
Define:
o Resource partitioning: The division of environmental resources by coexisting species
such that the niche of each species differs by one or more significant factors from the
niches of all coexisting species.
o Fundamental niche: which is the niche potentially occupied by that species, is often
different from its realized niche
o Realized niche: the portion of its fundamental niche that it actually occupies
Are partitions based on only space concerns?



o Time? : Species can partition their niches not just in space, as lizards and barnacles do,
but in time as well. This change in behavior suggests that competition exists between
the species and that partitioning of their active time helps them coexist.
 Example: he common spiny mouse (Acomys cahirinus) and the golden spiny
mouse (A. russatus) live in rocky habitats of the Middle East and Africa, sharing
similar microhabitats and food sources
Define:
o Character displacement: The tendency for characteristics to be more divergent in
sympatric populations of two species than in allopatric populations of the same two
species.
o Exploitation: A +/- ecological interaction in which one species benefits by feeding on the
other species, which is harmed. Exploitative interactions include predation, herbivory,
and parasitism.
o Predation: An interaction between species in which one species, the predator, eats the
other, the prey.
 Example: Though the term predation generally elicits such images as a lion
attacking and eating an antelope, it applies to a wide range of interactions.
Define, with an example:
o Mechanical defense: For example, porcupine.
o Chemical defense: For example, skunk.
o Aposematic coloration: The bright warning coloration of many animals with effective
physical or chemical defenses. For example, poison dart frog
o Cryptic coloration: Camouflage that makes a potential prey difficult to spot against its
background. For example, tree frog
o Batesian mimicry: A type of mimicry in which a harmless species resembles an
unpalatable or harmful species to which it is not closely related. For example, hawk
moth larva
o Muellerian mimicry: Reciprocal mimicry by two unpalatable species. For example,
cuckoo bee and yellow jacket
Define:
o Herbivory: An interaction in which an organism eats part of a plant or alga.
o Parasitism: A+/− ecological interaction in which one organism, the parasite, benefits by
feeding upon another organism, the host, which is harmed; some parasites live within
the host (feeding on its tissues), while others feed on the host’s external surface.
o Host: The larger participant in a symbiotic relationship, often providing a home and food
source for the smaller symbiont.
o Endoparasites: A parasite that lives within a host.
o Ectoparasites: A parasite that feeds on the external surface of a host.
o Positive interaction: A +/+ or +/0 ecological interaction in which at least one of the
interacting species benefits and neither is harmed; positive interactions include
mutualism and commensalism.
o Mutualism: A+/+ ecological interaction that benefits each of the interacting species.
o Commensalism: A+/0 ecological interaction in which one organism benefits but the other
is neither helped nor harmed.
Diversity and trophic structure characterize biological communities


Define:
o Species diversity: The number and relative abundance of species in a biological
community.
o Species richness: The number of species in a biological community.
o Relative abundance: The proportional abundance of different species in a community.
Can species richness and relative abundance be very different from one another?
o : The species richness is the same for both communities because they both contain four
species of trees, but the relative abundance is very different (Figure 54.11). You would
easily notice the four types of trees in community 1, but unless you looked carefully, you
might see only the abundant species A in the second forest. Most observers would
intuitively describe community 1 as the more diverse of the two communities.




Define:
o Shannon diversity index: An index of community diversity symbolized by H and
represented by the equation H=–(pA ln pA+pB ln pB+pC ln pC+. . .), where A, B, C …
are species, p is the relative abundance of each species, and ln is the natural logarithm.
o H =: −(pA ln pA+pB lnpB+pC lnpC+…)
o What does a higher H value indicate?
 : indicates a more diverse community.
 Example: calculate the Shannon diversity index of the two communities
o How is determining abundance and richness difficult?
 : Because most species in a community are relatively rare, it may be hard to
obtain a sample size large enough to be representative.
 : It can also be difficult to identify some of the species in the community. If an
unknown organism cannot be identified on the basis of morphology alone, it is
useful to compare all or part of its genome to a reference database of DNA
sequences from known organisms.
What is the relationship between diversity and productivity?
o : Higher-diversity communities generally are more productive and are better able to
withstand and recover from environmental stresses, such as droughts.
o Example: In one decade-long experiment, for instance, researchers at Cedar Creek
created 168 plots, each containing 1, 2, 4, 8, or 16 perennial grassland species.
Define:
o Biomass: The total mass of organic matter comprising a group of organisms in a
particular habit
o Invasive species: A species, often introduced by humans, that takes hold outside its
native range
o Trophic structure: The different feeding relationships in an ecosystem, which determine
the route of energy flow and the pattern of chemical cycling.
o Food chain: The pathway along which food energy is transferred from trophic level to
trophic level, beginning with producers.
o Trophic level: The position an organism occupies in a food chain is called its trophic
level
o Food Web: The interconnected feeding relationships in an ecosystem.
Define the members of a food chain:




o Primary producer: An autotroph, usually a photosynthetic organism. Collectively,
autotrophs make up the trophic level of an ecosystem that ultimately supports all other
levels. For example, the primary producers are phytoplankton, which serve as food for
the dominant grazing zooplankton, especially krill and copepods, both of which are
crustaceans.
o Primary consumer: An herbivore; an organism that eats plants or other autotrophs.
o Secondary consumer: A carnivore that eats herbivores.
o Tertiary consumer: A carnivore that eats other carnivores.
o Quaternary Consumer:_____________________________________
What is the relative abundance of each member of the food chain?
o :_____________________________________
o :_____________________________________
o :_____________________________________
o :_____________________________________
o :_____________________________________
Define:
o Energetic hypothesis: The concept that the length of a food chain is limited by the
inefficiency of energy transfer along the chain.
o Dominant species: A species with substantially higher abundance or biomass than other
species in a community. Dominant species exert a powerful control over the occurrence
and distribution of other species.
o Keystone species: A species that is not necessarily abundant in a community yet exerts
strong control on community structure by the nature of its ecological role or niche.
 Example 1: In rocky intertidal communities of western North America, the
relatively uncommon sea star Pisaster ochraceus preys on mussels such
as Mytilus californianus, a dominant species and strong competitor for space.
 Example 2:_____________________________________
o Ecosystem engineers: An organism that influences community structure by causing
physical changes in the environment.
 Example: By felling trees, building dams, and creating ponds, beavers can
transform large areas of forest into flooded wetlands
Compare these two models:
o Top-down model: A model of community organization in which predation influences
community organization by controlling herbivore numbers, which in turn control plant or
phytoplankton numbers, which in turn control nutrient levels; also called the trophic
cascade model.
o Bottom-up model: A model of community organization in which mineral nutrients
influence community organization by controlling plant or phytoplankton numbers, which
in turn control herbivore numbers, which in turn control predator numbers.
Define:
o biomanipulation: An approach that applies the top-down model of community
organization to alter ecosystem characteristics. For example, ecologists can prevent
algal blooms and eutrophication by altering the density of higher-level consumers in
lakes instead of by using chemical treatments.
Disturbance influences species diversity and composition

Define:
o Stability:_____________________________________
o Climax community:_____________________________________
o Disturbance:_____________________________________
 Examples:_____________________________________
o Nonequilibrium model:_____________________________________





o Intermediate disturbance hypothesis:_____________________________________
Why/How would high levels of disturbance reduce diversity?
o :_____________________________________
o :_____________________________________
Why/How would moderate levels of disturbance increase diversity?
o :_____________________________________
o :_____________________________________
Define:
o Ecological succession:_____________________________________
 Example:_____________________________________
o Primary Succession:_____________________________________
 Example:_____________________________________
How would you classify the colonization of glacier bay?
o :_____________________________________
o Why? :_____________________________________
Define:
o Secondary Succession:_____________________________________
 Example:_____________________________________
o Human disturbance:_____________________________________
 How significant is this? :_____________________________________
Biogeographic factors affect community diversity



What is a latitudinal gradient?
o :_____________________________________
How does sunlight and precipitation appear to effect diversity?
o :_____________________________________
o :_____________________________________
Define:
o Evapotranspiration:_____________________________________
o Potential evapotranspiration:_____________________________________





What is the importance of the species-area curve?
o :_____________________________________
o Define: S, c and Az :_____________________________________
o What does a z = 1 mean? :_____________________________________
 Z = 0 ? :_____________________________________
How does island area influence species richness?
o :_____________________________________
How does immigration and extinction influence richness?
o :_____________________________________
How does island size influence extinction rates?
o :_____________________________________
o Why? :_____________________________________
Define:
o Competitive exclusion:_____________________________________
o Island equilibrium model:_____________________________________
 What experiment(s)support this model?
 :_____________________________________
 :_____________________________________
Pathogens alter community structure locally and globally

Define:
o Pathogens:_____________________________________
o Examples:
 :_____________________________________
 :_____________________________________
o Zoonotic pathogens:_____________________________________
 Examples:_____________________________________
o Vector:_____________________________________
 Examples:_____________________________________
I recommend you review the Concept Check questions as you go through the chapter. They are
excellent sources of practice for the exam.