College Biology Chapter 45 Notes: Community Ecology

all but section 45.10

By Mr. M

What is the difference between a biological community & an ecosystem?

• A community is all the species that live in a defined area (the biotic)

• An ecosystem includes the community plus the physical environment (biotic & abiotic factors)

• What’s the difference between an organism’s habitat & its niche?

• The place where a species normally lives is a habitat• An ecological niche is defined by the role an organism has

in its habitat as well as the resource parameters needed for its survival (ex. what it eats, what eats it, temp. range tolerance, places it can breed)

What is community structure?• Species Diversity

• Communities vary in their species diversity

• Two components of species diversity:• Species richness: the number of species

• Species evenness: the relative abundance of each species

• Factors influencing community structure;– Abiotic factors such as climate

– Gradients of topography, geology

– Species interactions (direct and indirect)

What is symbiosis?

• Symbiosis refers to direct, long-term interactions: kinds?

• Commensalism: One species benefits and the other is neither benefited nor harmed (ex. epiphytes & tree they perch on)

• Mutualism: Both benefit (ex. honeybees & flowers they pollinate)

• Parasitism: Parasite benefits, host is harmed (ex. endoparasites, ectoparasite, brood parasites, & parasitoids)

What are they?

Table 45-1 p810

What do we call it when two or more organisms are trying to obtain the same resource or

resources?• Competition; may be intra-specific or inter-specific, so

what’s the difference?

• Intra; relates to members of the same species competing (two gray squirrels seeking a mate, a nesting site or food)

• Inter; relates to organisms of different species competing for resources

• Competition among individuals of the same species (intra) is more intense than inter-specific competition.

• The more similar the niches of two species are, the more intensely the species will compete

Inter-specific Competition• Interference competition

– One species actively prevents another from accessing a resource

• Exploitative competition

– Species reduce the amount of a resource available to the other by using that resource (first come, first served)

So, how does competition impact species?

• It can result in Competitive Exclusion; When two species require the same limited resource to survive or reproduce, the better competitor will drive the less competitive species to extinction in that habitat

• Competitors can coexist when their resource needs are not exactly the same; however, competition suppresses growth of both species

• Over time a diverging of niches typically occurs to reduce the competition pressure between species

How might these niches diverge over time?

• Resource partitioning; an evolutionary process by which species become adapted to use a shared limiting resource in a way that minimizes competition (directional selection)

• Example: Eight species of woodpecker in Oregon feed on insects and nest in hollow trees, but the details of their foraging behavior and nesting preferences vary

• Directional selection can also lead to character displacement; the range of variation for one or more traits is shifted in a direction that lessens the intensity of competition for a limiting resource

• Example: Where two species of salamanders coexist, differences in body length becomes more pronounced

Character Displacement in Salamanders

What is predation?

• An inter-specific interaction in which one species (predator) captures, kills, and eats another species (prey)

• Relative abundances of predators and prey shift over time in response to species interactions and changing environmental conditions

Predator Responses to Changes in Prey Density

• Type I response (passive predators)

– Number of prey killed depends on prey density (example; web-spinning spiders or coral polyps)

• Type II response

– Number of prey killed depends on the predator’s capacity to capture, eat and digest prey (example; wolves & caribou)

• Type III response

– Number of kills increases only when prey density reaches a certain level (example; coyotes & prey w, x, y, or z, learning required to kill prey, or prey capture hindered by hiding places)

Figure 45-9b2 p814

Sometimes cyclic patterns emerge

• Time lag in predator response to prey density can lead to cyclic changes in abundance

• When prey density is low, predators decline, prey are safer, prey numbers increase

• When prey density is high, predator numbers increase, prey numbers decline

How do predators & prey evolve together?

• Predators select for better prey defenses, and prey select for more efficient predators

• Prey defenses include exoskeletons, unpleasant taste, toxic chemicals or stings, and physical adaptations such as camouflage

• Predator and prey populations exert selective pressures on one another

• Genetic traits that help prey escape will increase in frequency

• Defensive improvements select for a countering improvement in predators

• Example: Spraying beetles and grasshopper mice

What kinds of defensive adaptations might we look for?

• Warning coloration– Many toxic or unpalatable species have bright colors

and patterns that predators learn to avoid• Mimicry

– A harmless animal looks like a dangerous one • Camouflage

– Body shape, color pattern and behavior that make an individual blend in with its surroundings

Warning Coloration and Mimicry

Camouflage in Prey and Predators

What about plants?

• Two general defenses have evolved in response to herbivory:• Some plants withstand and recover quickly from the

loss of their parts (quick regeneration)• Some plants have physical deterrents (spines,

thorns, tough leaves); or chemical deterrents (secondary metabolites that taste bad or sicken herbivores)

What is it called when habitats change?• Ecological Succession; process in which one array of

species replaces another over time

• It can occur in a barren habitat such as new volcanic land (primary succession) or a disturbed region in which a community previously existed (secondary succession)

• What factors influence succession?

• Species Composition; which species are present in a community depends on:– Physical factors such as climate, altitude, and soil type

– Biotic factors such as which species arrived earlier

– The frequency and extent of disturbances

Primary Succession: Alaska’s Glacier Bay

Secondary Succession

Intermediate Disturbance Hypothesis:species richness is greatest in communities where disturbances are moderate in intensity and frequency

3 Types of ecological species to key in on for study:

• Species that are especially sensitive to disturbances to the environment are called?

• Indicator species; first to do poorly when conditions change, so they can provide an early warning of environmental degradation

• Species that are dispersed from their home range and become permanently established in a new area are called?

• Exotic species; can outcompete native species, without competitors, predators, parasites and diseases that kept it in check in its own habitat

• Species that have a disproportionately large effect on a community relative to their abundance are called?

• Keystone species; when absent can decrease habitat species diversity

Ex. Credit: In your own words; summarize how beaver are a keystone species in Yellowstone, and how that was determined

(what evidence used)- cite sources