# Biology Chapter 4- Population Biology

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 yall) 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 Populations reproduce only at certain times. 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. When there is a delay such that population growth depends on past population sizes, the population may cycle or have chaotic dynamics.

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 human population growth to slow, but global human carrying capacity is not known. 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. Disease outbreaks and starvation are two factors that may increase with population density. 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 curves. Populations Groups of organisms of the

same species that live within a given area Key characteristics: Dispersion patterns Population density Growth rate BioEd Online Ostriches are nomadic, wandering in small groups. Aspen trees are quick

to pioneer areas that have been disturbed by fire. 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. Population size can be measured by several sampling techniques. 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 Examples: Bony fish Grasshoppers 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 Examples:

Sharks Elephants 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.

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