BISC 121 - Community Ecology Part 1 - Midterm 4

What is a biological community?

An assemblage of populations of various species living close enough for potential interaction.

What do ecologists call relationships between species in a community?

Interspecific interactions.

What are examples of interspecific interactions?

Competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism).

What can interspecific interactions affect?

The survival and reproduction of each species.

How can the effects of interspecific interactions be summarized?

Positive (+), negative (–), or no effect (0).

What is interspecific competition?

A (–/– interaction between species) that occurs when species compete for a resource in short supply.

What can strong competition lead to?

Competitive exclusion, local elimination of a competing species.

What does the competitive exclusion principle state?

That two species competing for the same limiting resource cannot coexist indefinitely in the same place (unless conditions change).

What is the total of a species’ use of biotic and abiotic resources called?

The species’ ecological niche.

What can an ecological niche also be thought of as?

An organism’s ecological role.

When can ecologically similar species coexist in a community?

If there are one or more significant differences in their niches.

What is resource partitioning?

Differentiation of ecological niches, enabling similar species to coexist in a community.

What may differ as a result of competition?

A species’ fundamental niche may differ from its realized niche.

What is a fundamental niche?

Abiotic environmental conditions it can survive and grow.

What is a realized niche?

The “actual” niche of the species (it can’t participate in its entire fundamental niche because of competition and predation).

Who pioneered the experiment removing Balanus?

Joseph Connell (1923–2020) UCSB.

What is character displacement?

A tendency for characteristics to be more divergent in sympatric populations (living together) of two species than in allopatric populations (living in different places) of the same two species.

What is an example of character displacement?

Variation in beak size between populations of two species of Galápagos finches.

What does Fig. 54-4 show?

Los Hermanos, G. fuliginosa, G. fortis, beak depth, Daphne, G. fuliginosa allopatric, G. fortis allopatric, sympatric populations, Santa María, San Cristóbal, beak depth (mm), percentages of individuals in each size class, 60 40 20 0 repeated across graphs.

What is predation?

A (+/– interaction) referring to interaction where one species, the predator, kills and eats the other, the prey.

What are some feeding adaptations of predators?

Claws, teeth, fangs, stingers, and poison.

What may finding prey involve?

Remarkable eyesight as in eagles, imaging infrared as in pit vipers, electrical sense as in sharks, echolocation as in bats or dolphins, and other special adaptations.

What are examples of behavioral defenses of prey?

Hiding, fleeing, forming herds or schools, self-defense, and alarm calls.

What types of defensive adaptations do many animals have?

Morphological and physiological defense adaptations (horns, strength, quills, chemicals like a skunk, size, etc.).

What is cryptic coloration?

Camouflage that makes prey difficult to spot.

What does the video “Seahorse Camouflage” relate to?

Cryptic coloration in insects.

What is the mimic octopus example showing?

That they are all the same animal.

What do animals with effective chemical defense often exhibit?

Bright warning coloration, called aposematic coloration.

What are examples of aposematic coloration?

Black with white stripe (skunk) or black and yellow stripes (hornets and bees).

How do predators typically respond to aposematic coloration?

They are particularly cautious in dealing with prey that display such coloration.

What can a prey species gain by mimicking another species?

Significant protection by mimicking the appearance of another species.

What is Batesian mimicry?

When a palatable or harmless species mimics an unpalatable or harmful model.

What textbook error is noted about the Cuckoo bee?

It apparently does not sting and may use Batesian mimicry.

What is Müllerian mimicry?

When two or more “unpalatable” (or well defended) species resemble each other and reinforce negative learning from potential predators.

What may self-defense sometimes involve?

Just being powerful; horns help, too.

What does the repeated phrase “Sht sht sht sht sh*t” refer to?

A reaction in the context of self-defense (with YouTube video link referenced).

What is herbivory?

A (+/– interaction) referring to an interaction in which an herbivore eats parts of a plant or alga.

What has herbivory led to?

Evolution of plant mechanical and chemical defenses and adaptations by herbivores.

What is symbiosis?

A relationship where two or more species live in direct and intimate contact with one another.

What is parasitism?

A (+/– interaction) in which one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process.

What are endoparasites?

Parasites that live within the body of their host.

What are ectoparasites?

Parasites that live on the external surface of a host.

What is notable about many parasites’ life cycles?

They have a complex life cycle involving a number of hosts.

What can some parasites change in their hosts?

The behavior of the host to increase their own fitness.

What is mutualistic symbiosis or mutualism?

A (+/+ interaction), an interspecific interaction that benefits both species.

What is an obligate mutualism?

A mutualism where one species cannot survive without the other.

What is a facultative mutualism?

A mutualism where both species can survive alone.

What examples are referenced for facultative or general mutualisms?

Root nodules, rumen in cattle, luminous bacteria in fish, vent worms.

What does the video “Clownfish and Anemone” relate to?

Mutualism.

What is an example of mutualism

An acacia tree and ants (genus Pseudomyrmex). Ants can clear out an area at the base of the acacia tree.

What is commensalism?

A (+/0 interaction) in which one species benefits and the other is apparently unaffected.

Why are commensal interactions hard to document in nature?

Because any close association likely affects both species.

What does Fig. 54-9 show?

Commensalism (image reference).

What do a few species in a community often exert?

Strong control on that community’s structure.

What are the two fundamental features of community structure?

Species diversity and feeding relationships.

What is species diversity of a community?

The variety of organisms that make up the community.

What are the two components of species diversity?

Species richness and relative abundance.

What is species richness?

The total number of different species in the community.

What is relative abundance?

The proportion each species represents of the total individuals in the community.

What can two communities have the same of?

The same species richness but a different relative abundance.

What can diversity be compared with?

A diversity index.

What is an example of a diversity index?

Shannon diversity index (H).

What is the formula for the Shannon diversity index (H)?

H = –[(pA ln pA) + (pB ln pB) + (pC ln pC) + …].

What is pA in the Shannon index formula?

The proportion of species A.

What is noted about the Shannon index formula?

It relates to “Information Content” in the distribution and does not need to be memorized.

When is determining the number and abundance of species in a community especially difficult?

When doing it for small organisms.

What can help determine microbial diversity?

Molecular tools.

What are two examples of microbial diversity studies with Bacteria?

Soil diversity and marine plankton diversity.

What do results for bacteria in marine plankton show?

Measured richness with highest diversity only at lower latitudes, following the general “rule” of diversity decreasing with latitude for animals and plants.

What note is given about the marine plankton study?

It is not in the textbook (published by Fuhrman et al., PNAS 2008).

What has work with experimental plant communities shown about more diverse communities?

That they tend to be more productive and also better at withstanding and recovering from environmental stresses, such as drought.

How do more diverse communities respond to invasive species?

They better resist invasive species, as shown in experimental invertebrate communities.

What is trophic structure?

The feeding relationships between organisms in a community.

What is trophic structure a key factor in?

Community dynamics.

What do food chains do?

Link trophic levels from producers to top carnivores.

What does the terrestrial food chain example show?

A plant (primary producer), a herbivore (primary consumer), and carnivores at secondary, tertiary, and quaternary consumer levels.

What does the marine food chain example show?

Phytoplankton (primary producers), zooplankton (primary consumers), and carnivores at successive trophic levels.

What is a food web?

A branching food chain with complex trophic interactions, more realistic than a food chain.

What does D.O.M. stand for?

Dissolved Organic Matter.

How much of the total material flow does D.O.M. pass?

Half or more.

What do food webs include?

Microorganisms as critical links, not just decomposers.

What does the Aquatic Planktonic Food Web figure show?

That species may play roles at more than one trophic level. Decomposers that feed on multiple levels are
obvious examples. Other food webs include organisms that
change greatly in size over development.

Which organisms are obvious examples of feeding on multiple levels?

Decomposers.

What other organisms may feed at multiple levels?

Organisms that change greatly in size over development.

How can food webs be simplified?

By isolating a portion of a community that interacts very little with the rest of the community.

What is the trophic role of the sea nettle?

It is a secondary or tertiary consumer depending on the path.

What is the trophic role of the sea bass?

It is at multiple levels depending on life stage.

How long is each food chain in a food web usually?

Only a few links long.

What does the energetic hypothesis suggest?

That food chain length is limited by inefficient energy transfer.

What does the dynamic stability hypothesis propose?

That long food chains are less stable than short ones.

Which hypothesis is supported by most data?

The energetic hypothesis.

What does Figure 54.17 test?

The energetic hypothesis for the restriction of food chain length.

What does the figure’s experiment use?

Tree holes in Australia.

What are the productivity levels compared in the experiment?

High (natural rate of litter fall), Medium (1/10 natural rate), Low (1/100 natural rate).

What do certain species have in a community?

A very large impact on community structure.

What are such species characterized by?

Being highly abundant or playing a pivotal role in community dynamics.

What are dominant species?

Species that are most abundant or have the highest biomass.

What is biomass?

The total mass of all individuals in a population.

What do dominant species exert?

Powerful control over the occurrence and distribution of other species.

What is one hypothesis about dominant species?

That they are most competitive in exploiting resources.