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What is Population Ecology? focuses on the factors that influence pop size. A populations geographic boundaries may be natural as with certain species of trout in an isolated lake. -the definition of populations changed according to the ecologist to fit the research. Populations Density number of individuals of a species per unit area or volume. -EXAMPLE- number of oak trees in a forest covering 50 km2 its impractical l to count all individuals in a pop. ecologist use variety of sampling techniques to estimate pp density. EXAMPLE- alligators in the Florida everglades pop estimated by taking the sample plot of 1 km2 another technique to estimate the populations is MARK-RECAPTURE METHOD this method the researchers places traps within the boundaries of the populations under study. -the researcher marks the animal and releases it., after few days the marked animals mix with unmarked the traps set again. -the second capture will yield both marked and unmarked individuals to mix . Using that data the population is estimated Pattern of Dispersion way individuals are spaced within the populations geographic range/, clumped pattern most common. Clumping results the unequal distribution of resources. -clumping often associated with uneven food distribution/mating/social behavior. Example, mosquitoes clump to increase mating chance. A uniform pattern of dispersion often result from interactions among the individuals of a population/ EXAMPLE creosote bushed in the desert are spaced because their roots compete for water and dissolved nutrients. RANDOM dispersion individuals on a population are spaced patternless unpredictable ways. Clams in years when they are mating and the food is plenty unevenly distribute themselves. Some population show both clumped and uniform distribution pattern s but on diff scales.
Population Ecology
Population growth models a small pop in a favorable environment way increase rapidly for awhile but eventually the numbers must as a result of limited resources and other factors stop growth. The growth rate is the change in pop size per interval. The growth rate is equal to the number of births minus the the number of deaths. The exponential Growth Model: The ideal of an Unlimited Environment - the rate of expansion of a population under ideal, unregulated conditions is described by the exponential growth model, in which the whole population multiplies by a constant factor during constant time intervals. - The E.G model gives an idealized picture of the unregulated growth of a population. The Logistic Growth Model: The reality Of a limited Environment environmental-limiting factors- environmental factors that restrict population growth Logistic growth model- a description of idealized population growth that is slowed by limiting factors. Carrying capacity- is the number of individuals in a population that the environment can just maintain with none increase or decrease. AREGULATION OF POPULATION GROWTH Density- Dependent Factor the major biological assumption of the logistic model is that increasing population density reduces the resources available for individual organism, ultimately limiting pipulation growth. Intraspecific competition- competition between the same species for a limited resource, as population increases comp. Become intense and the growth rate declines. A density dependent factor- is a pop limiting factor whose effects intensity as the pop increases in density. -affects a greater percentage of individuals in a pop as the number of individuals increase. EX Poisonous wastes these factors depress a pops growth rate and increase death rate. Density independent factors a population whose intensity is unrelated to population density is called Density- independent factor. Ex-change sin weather ex- a freeze in fall kill insects in many natural populations density independent factors limit population size well before resources or other density dependent factors become important. Floods storms, habitat changes and human activity can affect population in a density independent manner. Over long time most population are probably regulated by a mix of density dependent factors and density independent factors. population limiting factors that contribute to carrying capacity. Ecologist classify them into two castigators density dependent factort a low population level the resources are abundant and the pop is able to grow nearly exponentially.
HUMAN Population GROWTH The history of Global population Growth the human population has increased tremendously, compared to the past. Humans have spread out through the world, and the pop continues to grow but the growth cannot last forever. Prediction of human pop by 2025 is 7 to 8 million Age structure and population growth worldwide human population growth is a mosaic of various rates of growth in different countries. Sweden has a balance in the the growth rate because the death and birth rate balance each other out age structure of a population is the proportion of individuals in different age groups. In Italy individuals younger than reproductive age are relatively underrepresented in the population this contributes to that country's slightly negative population growth.
