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Biology Chapter 4- Population Biology Population Limiting factor Exponential growth Carrying capacity Life-history patterns Density R strategy K strategy Competition More Vocabulary • • • • • • • Stress Crowding Demography Birthrate Deathrate Doubling time Age structure Population Growth • J Curve • http://cauchy.math.colostate.edu/Applets/E xponentialGrowth/exponentialgrowth.htm • Limits to growth (Limiting Factors y’all) – Biotic and abiotic • Carrying Capacity • Exponential growth • Page 94 growth graph and explaination More graphing • Add carrying capacity • http://cauchy.math.colostate.edu/Applets/L ogisticGrowth/logisticgrowth.htm Life History patterns • Rapid Life history • Slow life history • K reproduction strategy (but intrinsic, not conscious) • R reproduction strategy • http://www.sumanasinc.com/webcontent/a nimations/content/tradeoffs.html Population Density Patterns – Random – Clumped – Uniform Limiting Factors • Density-dependent – Disease – Competition • Density-independent – Usually abiotic Organism interactions • Predation – Graph p 98 • Interspecies competition • Intraspecies competition • Effects of crowding Addendum • An S shaped curve is logistic growth • This is the more common representation of population growth Basic Characteristics of Populations • The suitability of habitats influences the geographic distribution of a species. • Insights can be gained by studying the spatial distributions of populations within habitats. Population Age Structure • Differences in environmental conditions and past history may cause populations to differ in their age distributions. • The future growth of a population depends on its current age distribution. Density-Independent Population Growth • Simple models describe how idealized populations would grow in an infinite environment. • In these models, populations increase to infinity or decrease to zero. • Continuous Model – Reproduction occurs in the population at all times. • Discrete Model Density-Dependent Population Growth • In density dependent population growth, the per capita growth rate decreases as the population approaches a carrying capacity. • When population growth rate depends on current population size, the population smoothly approaches carrying capacity. Dynamics of Lagged Logistic Growth Models • As growth rate increases, populations overshoot carrying capacity (K). • Further increases cause the population to cycle. Human Population Growth • Human population growth does not currently show density effects that typically characterize natural populations. • In natural populations, per capita population growth rate decreases with population size, whereas global human population growth rate has a positive relationship. • Human population growth rate has been growing more than exponentially. • Limited resources eventually will cause Density-Dependent and Density-Independent Effects on Populations • In many habitats, the forces that limit population sizes are independent of population density. For example, extreme weather events may decrease populations. • For most species, density-dependent factors limit birth rates or increase death rates at least some of the time. This type of population determination often is referred to as “regulation.” r-selected Reproductive Strategy • r-selected Species: – have high reproductive rates – tend to occur in unpredictable environments – typically have type III survivorship curves K-selected Reproductive Strategy • K-selected Species: – occur near carrying capacity – experience effects of population density – have low reproductive rates, high parental care – have type I survivorship Populations • Groups of organisms of the same species that live within a given area • Key characteristics: Ostriches are nomadic, wandering in small groups. – Dispersion patterns – Population density – Growth rate Aspen trees are quick to pioneer areas that have been disturbed by fire. BioEd Online Dispersion Patterns Within Populations Three common patterns of population distribution are: BioEd Online Population Density • Population density is total population size per unit of area. • Population densities depend on: – Interactions within the environment – Quality of habitat – Density dependent factors – Density independent factors • Carrying capacity is the maximum number of organisms that can be supported in a given habitat. BioEd Online Population Growth Exponential vs. Logistical Growth BioEd Online Survivorship in Populations BioEd Online Reproductive Strategies • r- Selected (maximum growth rate, below carrying capacity) – – – – Early reproduction Short life span High mortality rate Little or no parental care – Large investment in producing large numbers of offspring – Below carrying capacity BioEd Online • K-Selected (maximizes population size near carrying capacity) – – – – Late reproduction Long life span Low mortality rate Extensive parental care – Greater investment in maintenance and survival of adults – At or near carrying capacity Limits on Population Growth • Density Dependent Limits – Food – Water – Shelter – Disease Water and shelter are critical limiting factors in the desert. • Density Independent Limits – Weather – Climate BioEd Online Fire is an example of a Density independent Limiting factor.