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Lecture

BIOD60H3 Lecture Notes - Secondary Succession, Intermediate Disturbance Hypothesis, Primary Succession


Department
Biological Sciences
Course Code
BIOD60H3
Professor
S

Page:
of 5
CHAPTER 55- COMMUNITY ECOLOGY
55.1 WHAT ARE ECOLOGICAL COMMUNITIES
Species that live and interact in an area constitute an ecological community
Ecological communities are not assemblages of organisms that move together
as units when environmental conditions change, rather each species has
unique interactions with its biotic and abiotic environments
Organisms in a community can be divided into trophic levels based on their
source of energy
Trophic level: consists of the organisms whose energy source has passed
through the same # of steps to reach them
Photosynthesizers=primary producers
All nonphotosynthetic organisms (heterotrophs) consumer either directly or
indirectly the energy-rich organic molecules produced by primary producers
Primary consumers: eat plants constitute a trophic level called herbivores
Secondary consumers: eat herbivores
Decomposers: detrivores eat dead bodies
Organisms that obtain food from more than one trophic level are omnivores
Sequence of interactions in which a plant is eaten by an herbivore, which is in
turn eaten by a secondary consumer-food chain; food web
Most communities have 3-5 trophic levels; biomass: weight of living matter
in most terrestrial ecosystems photosynthetic plants dominate, both in terms
of the energy they represent and the biomass they contain
mammals may consume 30-40 percent of the annual aboveground grassland
plant biomass; insects may consume an additional 5=15 percent; soil
organisms 6-40 percent of the belowground biomass in grasslands
in aquatic ecosystems, dominant photosynthesizers are bacteria and protists ;
high rates of cell division
predators restrict habitat and geographic distribution of their prey
austrialian biogeographic region is home to a birds- megapodes (mound-
builders) that don’t incubate eggs; lay eggs in a mound of decomposing
vegetable material; warmed by decomposition; parent visits regularly to add or
remove decaying material for temperature
prey species have evolved a rich variety of adaptations that make them
difficult to capture, subdue and eat; toxic hairs, bristles, tough spines, noxious
chemicals, camouflage and mimicry of inedible objects or of larger dangerous
animals
Batesian mimicry: palatable species may mimic an unpalatable or noxious
one-process; works because a predator that captures an individual of an
unpalatable or noxious species learns to avoid other prey individuals of similar
appearance
Mullerian mimicry: two or more unpalatable or noxious species may
converge to resemble one another
for a microparasite to persist in a host population, atleast one new host must
become infected with the microparasite before each infected host dies
3 distinct clases: susceptible, infected and recovered
A microparasite can readily invade a host pop’n dominated by susceptible
individuals but as infection spreads, fewer and fewer susceptible remain; a
point is met where infected don’t transmit infection to atleast one other;
infection dies out
Microparasite can be passed by direct body contact, breath, body fluids waste
products
All species share at least part of their diet and use of other resources with
others but resource sharing influences abundances and distributions of species
only if individuals reduce the ability of others to access resources, either by
interfering with their activites- interference competition-or by reducing the
availability resources-exploitation competition
Intraspecific competition-among individuals of same species-may result in
reduced growth and reproductive rates, may exclude some from habitats and
cause death
Interspecific competition-among different species
Competitive exclusion: a superior competitor can prevent all members of
another species from using a habitat
Photosynthetic plants typically compete for space, sunlight, water, minerals
Sessile animals may restrict their habitat distribution; Balabus balanoides(bb)
and Chthamalus stellatus (ch); adult ch live higher in the intertidal zone than
bb, little overlap between areas occupied by two species
Joseph Connell showed that vertical range of adults of each species is greater
in absence of other species
Species can restrict range of another species by reducing populations of shared
prey to such low levels that the other species cannot persist
Amensalisms are widespread and inevitable interactions
There is no benefit to the mammals in trampling the plants; destruction of the
plants is unintentional but inevitable
Mammal disturbs multitudes of insects in the grass, crushing some and
inadvertently consuming in an amensal relationship
Commensal relationship has evolved between large herbivores and some birds
that are predators of insects
Mutaulistic interactions exist between plants and microorganisms, fungi and
protists, plants and insects, animals and plants
Corals gain energy from photosynthetic protists living within their tissue; in
exchange they give protists nutrients from teh small planktonic animals they
capture
Terrestrial plants have mutualistic associations with animals; plants depend on
animals to move their pollen and provide those animals with nutrient rich
rewards; plants benefit b/c pollen is carried to other plants and receive pollen
to fertilize their ovules; animals benefit from food nectar and pollen; many
seed dispersers are also seed predators that destroy some of the seeds they
remove from plants
55.3 HOW DO SPECIES INTERACTIONS CAUSE TROPHIC CASCADES
Interactions of a single predator species in a community can cause a
progression of indirect effects across successively lower trophic levels-trophic
cascade
can be illustrated by wolf pop’n in Lamar Valley of Yellowstone National Park
wolves feed on pronghorn, mule, deer, elk, bison
share prey with coyotes, lions and bears