organism population community ecosystem biosphere Population Ecology Why

organism population community ecosystem biosphere Population Ecology

Why Population Ecology? § Scientific goal uunderstanding the factors that influence the size of populations § general principles § specific cases § Practical goal umanagement of populations § increase population size w endangered species § decrease population size w pests § maintain population size w fisheries management n maintain & maximize sustained yield

Life takes place in populations § Population ugroup of individuals of same species in same area at same time § rely on same resources § interact § interbreed Population Ecology: What factors affect a population?

Factors that affect Population Size § Abiotic factors usunlight & temperature uprecipitation / water usoil / nutrients § Biotic factors uother living organisms § prey (food) § competitors § predators, parasites, disease § Intrinsic factors uadaptations

Characterizing a Population § Describing a population upopulation range upattern of Dispersion u. Density of population u#individuals per unit area 1970 1966 1964 1960 1965 1961 Equator 1958 1951 1943 1937 1956 1970 Immigration from Africa ~1900 range

Population Range § Geographical limitations uabiotic & biotic factors § temperature, rainfall, food, predators, etc. uhabitat adaptations to polar biome adaptations to rainforest biome

Population Dispersion § Spacing patterns within a population Provides insight into the environmental associations & social interactions of individuals in population clumped Why clump? random Why uniform? uniform Why random?

Population Size § Changes to population size can occur by:

Population Growth Rates § Factors affecting population growth rate usex ratio § how many females vs. males? ugeneration time § at what age do females reproduce? uage structure § #females at reproductive age in cohort?

Why do teenage boys pay high car insurance rates? Demography § Study of a populations vital statistics and how they change over time § Life tables, Age Structure Diagrams and Survivorship Graphs Life table females What adaptations have led to this difference in male vs. female mortality?

Age structure § Relative number of individuals of each age What do these data imply about population growth in these countries?

Survivorship curves § Graphic representation of life table The relatively straight lines of the plots indicate relatively constant rates of death; however, males have a lower survival rate overall than females. Belding ground squirrel

Survivorship curves What do these graphs tell about survival & strategy of a species? § Generalized strategies Survival per thousand 1000 Human (type I) I. High death rate in post-reproductive years Hydra (type II) 100 II. Constant mortality rate throughout life span Oyster (type III) 10 1 0 25 50 75 Percent of maximum life span 100 III. Very high early mortality but the few survivors then live long (stay reproductive)

Trade-offs: survival vs. reproduction § The cost of reproduction u. To increase reproduction may decrease survival: (think about…) § age at first reproduction § investment per offspring § number of reproductive cycles per lifetime § parents not equally invested § offspring mutations Natural selection favors a § Life History determined by costs life history that maximizes and benefits of all adaptations. lifetime reproductive success

Reproductive strategies § K-selected ulate reproduction ufew offspring uinvest a lot in raising offspring § primates § coconut § r-selected K-selected uearly reproduction umany offspring ulittle parental care § insects § many plants r-selected

Trade offs Number & size of offspring vs. Survival of offspring or parent r-selected K-selected “Of course, long before you mature, most of you will be eaten. ”

Survivorship Curves with Reproductive Strategy K-selection Survival per thousand 1000 Human (type I) Hydra (type II) 100 Oyster (type III) 10 r-selection 1 0 25 50 Percent of maximum life span 75 100

Population Growth Rate Models § Exponential growth u. Rapid growth u. No constraints § Logistic growth u. Environmental constraints u. Limited growth

Population Growth Math • Change in population = Births – Deaths • • • Per capita birth rate = b Per capita death rate = d # of individuals = N Rate of population growth (r) = b – d Survivorship = % surviving Ex: If there are 50 deer in a population, 13 die and 27 are born the next month. What is the population size the following month? – (Answer: 27 -13 = 14, so new population is 64) Ex: What is the birth rate for the deer? #Births/N = b – Answer: 27/50 =. 54 – Death rate (d) = 13/50 =. 26 Ex: What is the rate of growth for the deer? r =. 54 -. 26 =. 28

Exponential Growth • No environmental barriers • Growth is at maximum rate d. N/dt = rmax. N N = # individuals Rmax = growth rate (ideal conditions)

Exponential Growth § Characteristic of populations without limiting factors uintroduced to a new environment or rebounding from a catastrophe Whooping crane coming back from near extinction African elephant protected from hunting

Logistic rate of growth § Can populations continue to grow exponentially? Of course not! no natural controls K= carrying capacity What happens as N approaches K? effect of natural controls

Logistic Growth Equation d. N/dt = rmax. N(K-N)/K K = carrying capacity of population Ex: If a population has a carrying capacity of 900 and the rmax is 1, what is the population growth when the population is 435? 1 x 435 (900435)/900 = 224 What if the population is at 850? What if it is at 1010? Explain the results of each problem.

uvaries with changes in resources What’s going on with the plankton? 10 8 6 4 2 0 1915 1925 1935 Time (years) 1945 500 Number of cladocerans (per 200 ml) § Maximum population size that environment can support with no degradation of habitat Number of breeding male fur seals (thousands) Carrying capacity 400 300 200 100 0 0 10 20 30 40 Time (days) 50 60

Changes in Carrying Capacity • Population cycles – predator – prey interactions K K

Regulation of population size marking territory = competition § Limiting factors udensity dependent § competition: food, mates, nesting sites § predators, parasites, pathogens udensity independent § abiotic factors w sunlight (energy) w temperature w rainfall competition for nesting sites swarming locusts

Introduced species § Non-native species (INVASIVE) utransplanted populations grow exponentially in new area uout-compete native species ureduce diversity uexamples § African honeybee § gypsy moth kudzu