1. Chapter 52: Population Ecology Population ecology Study of populations in relationship to the environment Study of populations in relationship to the environment Includes environmental influences on population density, distribution, age structure, & size Includes environmental influences on population density, distribution, age structure, & sizePopulation Individuals of one species simultaneously occupying the same general area, utilizing the same resources, & influences by similar environmental factors Individuals of one species simultaneously occupying the same general area, utilizing the same resources, & influences by similar environmental factors

2. Characteristics of populations Population density Population density Number of individuals per unit area Number of individuals per unit area Measuring density Measuring density Count all individuals in a representative sample area Count all individuals in a representative sample area Estimates based on indirect indicators such as nest, burrows, droppings, or tracks Estimates based on indirect indicators such as nest, burrows, droppings, or tracks Mark-recapture method Mark-recapture method Population dispersion Population dispersion The pattern of spacing among individuals within the designated geographic boundaries The pattern of spacing among individuals within the designated geographic boundaries Types Types Clumped Clumped Individuals are aggregated in patches Individuals are aggregated in patches Most common Most common Uniform Uniform Spacing of individuals is even Spacing of individuals is even Rare but territoriality is often the reason Rare but territoriality is often the reason Random Random Varies in an unpredictable way Varies in an unpredictable way Occurs in absence of strong attractions/repulsions of individuals Occurs in absence of strong attractions/repulsions of individuals Rare Rare Ex. Windblown dandelions Ex. Windblown dandelions

3. Demography Study of factors that affect the growth & decline of populations Study of factors that affect the growth & decline of populations Age structure & sex ratio Age structure & sex ratio Age structure Age structure Relative number of individuals of each age in the population Relative number of individuals of each age in the population Birth rate/fecundity Birth rate/fecundity Death rate Death rate Generation time Generation time The average span of time between birth of individual & the birth of their offspring The average span of time between birth of individual & the birth of their offspring Sex ratio Sex ratio Proportion of individuals of each sex found in a population Proportion of individuals of each sex found in a population Life Tables & survivorship curves Life Tables & survivorship curves Type I Type I Death rate increases in elderly but is flat for other ages Death rate increases in elderly but is flat for other ages Type II Type II Death rate constant throughout all age spans Death rate constant throughout all age spans Type III Type III Death rate high in young & elderly Death rate high in young & elderly

4. Life History Traits affecting organism’s schedule of reproduction & survival Traits affecting organism’s schedule of reproduction & survival Life histories are highly diverse but exhibit patterns Life histories are highly diverse but exhibit patterns Includes: Includes: When reproduction begins When reproduction begins How often an individual reproduces How often an individual reproduces How many offspring an individual produces How many offspring an individual produces Limited resources mandate tradeoffs between investment in reproduction vs. own survival Limited resources mandate tradeoffs between investment in reproduction vs. own survival Semelparity Semelparity Organism invests most of their energy into growth & development then expends all energy into a single reproductive effort before dying Organism invests most of their energy into growth & development then expends all energy into a single reproductive effort before dying Ex. Annual plants, salmon, bamboo Ex. Annual plants, salmon, bamboo Favored in highly variable, unpredictable environments with low offspring survival rates Favored in highly variable, unpredictable environments with low offspring survival rates Iteroparity Iteroparity Organism produces fewer offspring at a time but over several reproductive seasons Organism produces fewer offspring at a time but over several reproductive seasons Favored in dependable environments with high competition for resources Favored in dependable environments with high competition for resources

5. Population Growth Models Exponential model Exponential model Idealized population in an unlimited environment Idealized population in an unlimited environment Logistic model Logistic model Incorporates the concept of carrying capacity (K) Incorporates the concept of carrying capacity (K) Carrying capacity= maximum population size an environment can support Carrying capacity= maximum population size an environment can support

7. Regulation of Population Growth Intra-specific competition Intra-specific competition 2 or more individuals of the same species rely on a limited resource. 2 or more individuals of the same species rely on a limited resource. Density-dependant factors Density-dependant factors intensify as the population increases intensify as the population increases Competition for resources Competition for resources Territoriality Territoriality Health (i.e. disease) Health (i.e. disease) Predation Predation Toxic waste Toxic waste Intrinsic factors (i.e. stress syndrome in white footed mice) Intrinsic factors (i.e. stress syndrome in white footed mice)

8. Population Dynamics Study of the interactions between biotic & abiotic factors that cause variations in population size Study of the interactions between biotic & abiotic factors that cause variations in population size Some populations have regular boom & bust cycles Some populations have regular boom & bust cycles Small herbivores  lemmings show a 3-5 year cycle Small herbivores  lemmings show a 3-5 year cycle Large herbivores  snowshoe hare shows a 9-11 year cycle Large herbivores  snowshoe hare shows a 9-11 year cycle Insect  Cicada show a 13-17 year cycle Insect  Cicada show a 13-17 year cycle In some species crowding effects the endocrine system=reduced fertility In some species crowding effects the endocrine system=reduced fertility

10. Human Population Growth For centuries humans have appeared to grow exponentially… For centuries humans have appeared to grow exponentially… Agricultural revolution  increased birth rate & decreased death rate Agricultural revolution  increased birth rate & decreased death rate Industrial revolution  improved sanitation, nutrition, & health care Industrial revolution  improved sanitation, nutrition, & health care Can not grow indefinitely…. Can not grow indefinitely…. Population ecologists do not agree on the human carrying capacity Population ecologists do not agree on the human carrying capacity Age structure within each country causes variations in population growth Age structure within each country causes variations in population growth Humans can consciously control reproduction through contraception or government sponsored family planning Humans can consciously control reproduction through contraception or government sponsored family planning Agricultural & industrial technology has increased carrying capacity Agricultural & industrial technology has increased carrying capacity Social changes, individual choice, government intervention and/or increased mortality due to environmental limitations will cause the human population to stop growing Social changes, individual choice, government intervention and/or increased mortality due to environmental limitations will cause the human population to stop growing