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Population Ecology Chapter 6, pp.149-160 Populations and Communities Population: A group of organisms of a single species that live in a given area Metapopulation: a group of populations of the same species that exchange individuals occasionally Community: All the populations living in a given area True or False: a population made up of individuals of different species A. B. True False How can we describe a population? Size (N) = number of individuals Density = number of individuals per unit area (or volume in aquatic ecosystems) Distribution = random, clumped, or uniform Sex ratio = ratio of males to females Age structure = number of individuals in various age categories A scientist samples a 10 hectare field and estimates that the population of field mice is 350. What is the population density of field mice? Type your answer into your Qwizdom Density-Dependent Factors Factors that influence growth and survival depending on how large the population is Examples: Food Disease Space Sunlight Water Limiting Resources Resources that occur in smaller amounts than a population needs to grow in size If the amount of limiting resource declines, so does the size of the population All of the following are densitydependent factors EXCEPT A. B. C. D. Food supply Habitat Disease Temperature Carrying Capacity (K) The maximum number of individuals that can be supported in an environment Changes based on resource availability The number of individuals of a given species that can be supported by an ecosystem is A. B. C. D. Age structure Population density Limiting factor Carrying capacity Density-Independent Factors Factors that influence individuals regardless of population size Example: Tornados Hurricanes Floods Fires Temperature How do populations grow? Exponential Growth Intrinsic growth rate (r) = maximum possible growth rate for a population in ideal conditions Based on litter size and gestation time With no resource limitations populations grow exponentially (J curve) How do populations grow? Logistic Growth When population size approaches carrying capacity growth follows logistic model (S curve) Density-dependent factors limit growth When a population’s growth is limited by environmental factors, the growth model is A. B. C. D. Logistic, or S-shaped curve Exponential, or J-shaped curve Mitigated, or sine curve Value-added Overshoots and Die-offs Populations that exceed their carrying capacity (overshoot) then experience a large or small crash (die-off) Predator-Prey Relationships Predator and prey populations oscillate over time in some ecosystems Each population affects the size of the other Reproductive strategies K-selected species (K-strategists) Low reproductive rate, abundance determined by carrying capacity Large, reproduce relatively late, long gestation, few large offspring, nurturing parent r-selected species (r-strategists) High intrinsic growth rate, overshoot & die-off Small, frequent reproduction, large litters, short gestation, little parental care You discover a new species of bird that lays eggs once per year and spends approximately 6 months raising its offspring. This bird is an example of a A. B. C. D. R-strategist K-strategist Density independent factor Niche specialist