organism community ecosystem biosphere Population Ecology Chapter 55

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

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

Factors that affect Population Size § Abiotic factors u u u sunlight & temperature precipitation / water soil / nutrients § Biotic factors u other living organisms § prey (food) § competitors § predators, parasites, disease § Intrinsic factors u adaptations

Characterizing a Population § Describing a population range u pattern of spacing u § density u size of population 1970 1966 1964 1960 1965 1961 Equator 1958 1951 1943 1937 1956 1970 Immigration from Africa ~1900 range density

Population Range § Geographical limitations u abiotic & biotic factors § temperature, rainfall, food, predators, humans, etc. u habitat

Changes in range § Range expansions & contractions u changing environment aspen Elevation (km) 3 km oak, maple 15, 000 years ago glacial period Alpine tundra Spruce-fir forests white birch Alpine tundra sequoia Present Spruce-fir forests Mixed conifer forest Woodlands 2 km Mixed conifer forest 1 km 0 km Woodlands Grassland, chaparral, and desert scrub result of competition

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

Population Size § Changes to population size u adding & removing individuals from a population § § birth death immigration emigration

Population growth rates § Factors affecting population growth rate u sex ratio § how many females vs. males? u generation time § at what age do females reproduce? u age structure § how females at reproductive age in cohort?

Why do teenage boys pay high car insurance rates? Demography § Factors that affect growth & decline of populations u Life table vital statistics & how they change over time females What adaptations have led to this difference in male vs. female mortality?

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

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

Survivorship curves § Generalized strategies Survival per thousand 1000 Human (type I) Hydra (type II) 100 1 0 25 I. High death rate in post-reproductive years II. Constant mortality rate throughout life span Oyster (type III) 10 What do these graphs tell about survival & strategy of a species? 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 increase reproduction may decrease survival § age at first reproduction § investment per offspring § number of reproductive cycles per lifetime Natural selection favors a life history that maximizes lifetime reproductive success

Parental survival Kestrel Falcons: The cost of larger broods to both male & female parents

Reproductive strategies § K-selected u u u late reproduction few offspring invest a lot in raising offspring § primates § coconut § r-selected u u u K-selected early reproduction many offspring little 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. ”

Life strategies & survivorship curves K-selection Survival per thousand 1000 Human (type I) Hydra (type II) 100 Oyster (type III) 10 r-selection 1 0 25 50 75 Percent of maximum life span 100

Population growth change in population = births – deaths Exponential model (ideal conditions) d. N = ri. N growth increasing at constant rate dt N r ri t d = # of individuals = rate of growth = intrinsic rate = time = rate of change intrinsic rate = maximum rate of growth every pair has 4 offspring every pair has 3 offspring

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

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

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

Carrying capacity § Maximum u varies with changes in resources What’s going on with the plankton? Number of cladocerans (per 200 ml) population size that environment can support with no degradation of habitat 500 400 300 200 100 0 0 10 20 30 40 Time (days) 50 60

Changes in Carrying Capacity § Population cycles u predator – prey interactions At what population level is the carrying capacity? K K

Population of… China: 1. 3 billion India: 1. 1 billion Human population growth Doubling times 250 m 500 m = y () 500 m 1 b = y () 1 b 2 b = 80 y (1850– 1930) 2 b 4 b = 75 y (1930– 1975) What factors have contributed to this exponential growth pattern? Is the human population reaching carrying capacity? adding 82 million/year ~ 200, 000 per day! 2005 6 billion Significant advances in medicine through science and technology Industrial Revolution Bubonic plague "Black Death" 1650 500 million

Evolutionary adaptations § Coping with environmental variation u regulators § endotherms § homeostasis § (“warm-blooded”) u conformers § ectotherms § (“cold-blooded”)