Chapter 9 Population Dynamics, Carrying Capacity, and Conservation Biology Miller – Living in the Environment 13 th ed.

Population Dynamics - changes in populations as a result of environmental stress environmental stress changes in environmental conditions. changes in environmental conditions.

How do populations change over time? POPULATION ECOLOGY  # of individuals of a species in an area AND how/why those numbers change over time Effected by resource competition, predation, disease but can be measured

Major characteristics of a population 1)Size – number of individuals 2)Density – number of individuals in a certain space 3)Dispersion – spatial pattern of a population 4)Age distribution – proportion of individuals of each age in a population

Generalized dispersion patterns Most populations live in clumps although other patterns occur based on resource distribution. Most populations live in clumps although other patterns occur based on resource distribution.

Changes in Population Size: Entrances and Exits increase through births + immigration increase through births + immigration decrease through deaths + emigration decrease through deaths + emigration

biotic potential – capacity for population growth Intrinsic rate of increase (r) Intrinsic rate of increase (r) Life History Characteristics Life History Characteristics Reproduction age Reproduction range of age Reproductive periods # of offspring produced

Large Organisms have small biotic potential

organisms with a high biotic potential organisms with a high biotic potential reproduce early in life reproduce early in life have short generation times have short generation times can reproduce many times can reproduce many times have offspring each time they reproduce have offspring each time they reproduce Small Organisms have large biotic potential.

EX. Bacteria reproduce by dividing in half every 30 mins…. Plotting this growth vs. time results in a J shaped curve. EXPONENTIAL GROWTH results when pop are growing at biotic potential!

environmental resistance - factors acting to limit population growth No population can grow indefinitely. No population can grow indefinitely. There are always limits to population growth in nature. There are always limits to population growth in nature. Unfavorable env. conditions due to resource availability Unfavorable env. conditions due to resource availability As env conditions deteriorate, b  and d 

Carrying Capacity (K) Over time, the pop may level out to a certain point… called carrying capacity (K) the number of individuals of a given species that can be sustained indefinitely in a given space. the number of individuals of a given species that can be sustained indefinitely in a given space.

© 2004 Brooks/Cole – Thomson Learning Time (t) Population size (N) K Exponential Growth Logistic Growth Carrying capacity Population Growth Curves

Exponential and Logistic Population Growth: J-Curves and S-Curves Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

Exponential and Logistic Population Growth: J-Curves and S-Curves As a population levels off, it often fluctuates slightly above and below the carrying capacity. As a population levels off, it often fluctuates slightly above and below the carrying capacity.

What Happens When Populations Exceed Carrying Capacity Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.

Billions of people ? ? ? Mil years Hunting and gathering Black Death–the Plague Time Industrial revolution Agricultural revolution B.C.A.D. World Population Growth

Population Density Density-independent population controls Density-independent population controls Affect a population’s size regardless of its population density. Affect a population’s size regardless of its population density. Floods, fires, hurricanes habitat destruction, pesticides Floods, fires, hurricanes habitat destruction, pesticides Density-dependent population controls Density-dependent population controls Factors that impact population’s size considering density Factors that impact population’s size considering density Competition of resources, predation, parasitism, disease Competition of resources, predation, parasitism, disease

Types of Population Change Curves in Nature Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. (predator-prey oscillation) Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. (predator-prey oscillation)

Reproductive Patterns and Survival Asexual reproduction Asexual reproduction Offspring are exact copies of a single parent Offspring are exact copies of a single parent Sexual reproduction Sexual reproduction Organisms produce offspring by combining the gametes or sex cells from both parent Organisms produce offspring by combining the gametes or sex cells from both parentDisadvantages Females must produce twice as many offspring Females must produce twice as many offspring Chance of genetic errors increases Chance of genetic errors increases Mating entails costs Mating entails costsAdvantages Provides greater genetic diversity Provides greater genetic diversity Division of labor – males gather food and protect females and young Division of labor – males gather food and protect females and young

Figure 9-9 Page 196 Number of individuals Time Carrying capacity K species; experience K selection r species; experience r selection K Reproductive Patterns

r-Selected SpeciesOpportunists cockroach dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) carrying capacity (K) Generalist niche Low ability to compete Early successional species

Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species elephant saguaro K-Selected SpeciesCompetitors

Survivorship Curves: Short to Long Lives The way to represent the age structure of a population is with a survivorship curve. The way to represent the age structure of a population is with a survivorship curve. shows different reproductive strategies thus different life expectancies over time shows survivors at each age group of particular species Late loss population live to an old age. Late loss population live to an old age. Constant loss population die at all ages. Constant loss population die at all ages. Most members of early loss population, die at young ages. Most members of early loss population, die at young ages.

Percentage surviving (log scale) Age Survivorship Curves p. 198