Transcript Populations
14.3 Populations • group of organisms that belong to the same species and live in a particular place at the same time • measured in terms of size, density, dispersion, growth rate, age structure, and survivorship Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Size – the number of individuals that the population contains Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Density – Density is a measure of how crowded the population is – The measure of the number of individuals divided by the area they live in Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Dispersion – describes the distribution of individuals within the population – Three types • Random • Uniform • Clumped Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Three Patterns of Population Dispersion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Dynamics • Age Structure – indicates the percentage of individuals at each age Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Patterns of Mortality – Populations show three patterns of mortality or survivorship curves: • Type I (low mortality until late in life) • Type II (constant mortality throughout life) • Type III (high mortality early in life followed by low mortality for the remaining life span). Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Survivorship Curves Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 14.4 Population Growth Rate • Demographers, scientists who study population dynamics, define the growth rate of a population as the amount by which a population’s size changes in a given time • Population Size – Birth rate - death rate = growth rate Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The Exponential Model • describes perpetual growth at a steady rate in a population • assumes constant birth and death rates and no immigration or emigration Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The Logistic Model • birth rates fall and death rates climb as the population grows • When the carrying capacity is reached, the number of individuals the environment can support is reached and population growth becomes stable Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Two Population Growth Models Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Regulation • Population-limiting factors, such as competition, are density-dependent because the effect on each individual depends on the number of other individuals present in the same area. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Population Regulation • Population-limiting factors, such as bad weather and fires, are density-independent because the effect on each individual does not depend on the number of other individuals present in the same area. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Perils of Small Populations – Small populations have low genetic diversity and are subject to inbreeding, so they are less likely to adapt to environmental changes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 14.5 Community Stability – Disturbances can alter a community by eliminating or removing organisms or altering resource availability – Species richness may improve a community’s stability – Areas of low species richness may be less stable in the event of an ecological disturbance Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Ecological Succession • is a change in the species composition of a community over time • Primary Succession – is the assembly of a community on newly created habitat – occurs in areas that have been recently exposed to the elements and lack soil Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Ecological Succession • Secondary Succession – is the change in an existing community following a disturbance – occurs in areas where the original ecosystem has been cleared by a disturbance Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The Complexity of Succession • The traditional description of succession is that the community proceeds through a predictable series of stages until it reaches a stable end point, called the climax community. • Primary succession typically proceeds from lichens and mosses to a climax community. • Secondary succession typically proceeds from weeds to a climax community. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Ecological Succession at Glacier Bay Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.