Download - EK 4.A.5 Communities are composed of populations of organisms that interact in complex ways
Data Analysis and Mathematical Models
EK 4.A.5 Communities are composed of populations of organisms that interact
in complex ways
The structure of a community is described in terms of species composition and diversity
Communities are comprised of different populations of organisms that interact with each other in negative or positive ways
The physical structure of a community is affected by abiotic factors and also the spatial distribution of organisms
The mix of species in terms of both the number of individuals and the diversity of the species defines the structure of the community
Communities
Population InteractionsPredator/prey
relationships: Snowshoe Hare and Lynx
Changes in hare pop. is followed by similar changes in lynx pop. – predation limits hare pop. and food supply limits lynx pop.
Fluctuation cycles are commonly observed between predator and prey
Population InteractionsSymbiotic Relationships
Mutualism (+,+)Acacia trees provide food
& housing for ants; in exchange, resident ants kill any insects or fungi found on the tree and crop veg to increase sun exposure for tree
Lichen – algae provide sugar from photosynthesis; fungi provide minerals, water, attachment and protection
Population InteractionsCommensalism (+,0)Birds build nests in
tree (benefit from protection) the tree gets no benefit or harm
Egrets gather around cattle; birds get to eat insects that swarm around cattle; cattle are neither helped or harmed
Population InteractionsParasitism (+,-)Tapeworm live in the
digestive tract of animals, stealing nutrients from the host
http://youtu.be/rLtUk-W5Gpk
Population InteractionsIntroduction of Species
Competitive Exclusion occurs when two species compete for exactly the same resources (they occupy the same niche), one is likely to be more successful. One species outcompetes the other and eventually the second species is eliminated from the area
http://youtu.be/rZ_up40FZVw
Population InteractionsResource
Partitioning occurs when species coexist in spite of apparent competition for the same resources
Species do this by occupying slightly different niches
Population InteractionsWhich species of
paramecia outcompetes the other?Paramecium aurelia
PopulationsSize is usually
designated as N (total number of individuals)
Density – total number of individuals per area or volume
Dispersion – how individuals in a population are distributed
Growth Patterns & InteractionsAge structure – is a description of the abundance of
individuals of each ageRapid growth – many young, few elderly; developing
countriesSlow growth – larger at the bottom that slowly narrow; the
USZero growth – tiers of equal width; Italy
Growth Patterns & Interactions
About 1,000 years ago the human population began population growth thanks to increasing the carrying capacity of our environmentIncrease in food
supplyReduction in diseaseReduction in human
wasteExpansion of habitat
Growth Patterns and InteractionsSurvivorship Curves
describe how mortality of individuals in a species varies during their lifetimes
3 types of curvesType 1Type 2Type 3
Growth Patterns & InteractionsType 1 Survivorship
describe species in which most individuals live to middle age; after that mortality is high
Examples: Humans, Elephants
Growth Patterns & InteractionsType 2 Survivorship
describes organisms in which the length of survivorship is random, that is, the likelihood of death is the same at any age – constant death rate
Examples: Rodents and invertebrates
Growth Patterns & InteractionsType 3 Survivorship
describe species in which most individuals die young, with only a relative few surviving to reproductive age and beyond
Examples: oysters, plants, free-swimming larvae, frogs
Growth Patterns & InteractionsBiotic Potential is the
maximum growth rate of a population under ideal conditions
Take into consideration the following:Age at reproductive
maturityClutch sizeFrequency of reproductionReproductive lifetimeSurvivorship of offspring
to reproductive maturity
Growth Patterns & InteractionsLimits to Growth
Density-Dependent factors are those factors whose limiting effect becomes more intense as the population density increases
Examples – parasite & disease transmission; competition for resources; predation
Growth Patterns & InteractionsLimiting Growth
FactorsDensity-Independent
factors occur independently of the density of the population
Examples – natural disasters such as fires, earthquakes, volcanic eruptions; extreme climates such as storms and frosts
Growth Patterns & InteractionsExponential Growth in a
population occurs whenever the reproductive rate is greater than zero.
Producing a J shaped curve
G=rNG stands for growth, r
stands for the per capita rate of increase, and N stands for the population size
Growth Patterns & InteractionsLogistic Growth occurs when limiting factors restrict the size
of the population to the carrying capacity of the habitatProducing a S shaped curveG=rN*(K-N)/KK stands for the carrying capacity; as N approaches K the
growth rate is slowed, eventually reaching zero growth
Growth Patterns & InteractionsExponential and logistic growth patterns are
associated with two kinds of life-history strategies:R-selected speciesK-selected species
Growth Patterns & InteractionsR-selected species –
Rapid growth (J shaped curve)
Opportunistic species – grasses and insects
Quickly invade a habitat and reproduce immediately (after reproducing they die)
Produce many offspring that are small, mature quickly and require little if any parental care
Growth Patterns & InteractionsK selected species
Population size remains relatively constant at carrying capacity, K – s shaped curve
Produce few offspring that are larger in size and require extensive parental care
Reproduction occurs repeatedly during their lifetime
Growth Patterns & Interactions