Population Ecology Ecology environment components biotic abiotic Ecology
Population Ecology
Ecology • environment – components • biotic • abiotic
Ecology • Hierarchy of Ecology – biosphere – ecosystem – community – population – individual
Population Ecology • 2 characteristics of a population: – density – dispersion
Density • we measure density by sampling – mark and recapture method – line intercept method – point count method
Population Distribution • distribution patterns – clumped – uniform – random
Age Distribution • distribution of males and females in each age group of a population • used to predict future population growth
Survivorship • mirrors mortality • expressed in survivorship curves – plots surviving individuals at different age groups
Survivorship • three types of survivorship curves – late loss (Type I) – constant loss (Type II) – early loss (Type III)
Changes in a Population • 3 factors determine population changes – births – deaths – migration • immigration • emigration
Population Dynamics • J curve • exponential growth – measures optimal population growth • rmax = intrinsic rate of increase
Population Growth • example: – 10, 000 birds in a population – 1500 births and 500 deaths per year – 1500/10, 000 - 500/10, 000 =. 10 or 10% – expressed by saying there is a 10% increase per bird per year
Population Dynamics • size of a population is limited to: – intrinsic rate of increase – environmental resistance • includes limitations the environment imposes on birth rate and death rate in a population – – food space predation parasitism
Population Growth and Regulation • carrying capacity (K) • determined by – renewable resources like water, nutrients, and light – nonrenewable resources such as space
Carrying Capacity – logistic population growth – r decreases as N increases – K-N tells us # of individuals population can accommodate – S curve
Population Growth Models • K selected – equilibrial populations – live at density near limit imposed by resources • r selected – opportunistic populations – live in environments where little competition is present
Density Influence on Birth and Death Rates • 2 mechanisms – density independent – density dependent
Density Independent Factors • unrelated to population size • most important: – weather – climate
Density Dependent Factors • increase effectiveness as population density increases • especially affects long lived organisms • include – predation – parasitism – competition
Human Population Growth • J curve growth • grows at a rate of about 80 million yearly (r=1. 3%) • Why doesn’t environmental resistance take effect?
Human Population Growth • altering their environment • technological advances – the cultural revolution – the agricultural revolution – the industrial-medical revolution
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