Population Dynamics, Carrying Capacity, and Conservation Biology

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

A population Is a group of individuals of a single species living in the same general area

Major characteristics of a population Size – number of individuals Density – number of individuals in a certain space Dispersion – spatial pattern of a population 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.

A clumped dispersion Is one in which individuals aggregate in patches May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

A uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

A random dispersion Is one in which the position of each individual is independent of other individuals Figure 52.3c (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

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

biotic potential – capacity for population growth Intrinsic rate of increase (r) rate with unlimited resources organisms with a high biotic potential reproduce early in life have short generation times can reproduce many times have offspring each time they reproduce

environmental resistance - factors acting to limit population growth No population can grow indefinitely. There are always limits to population growth in nature.

Carrying Capacity (K) the number of individuals of a given species that can be sustained indefinitely in a given space.

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

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.

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.

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.

Black Death–the Plague Agricultural revolution 16 15 ? 14 13 12 11 ? 10 9 Billions of people 8 ? 7 6 5 World Population Growth 4 3 2 Black Death–the Plague 1 2-5 Mil years 8000 6000 4000 2000 2000 2100 Time B.C. A.D. Hunting and gathering Agricultural revolution Industrial revolution

Population density Density-independent population controls Affect a population’s size regardless of its population density. Floods, fires, hurricanes habitat destruction Density-dependent population controls Factors that have a greater effect as a population’s density grows Competition of resources, predation, parasitism, disease

Types of Population Change Curves in Nature Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Stable: fluctuates slightly above and below carrying capacity. Irruptive: populations explode and then crash to a more stable level. Irregular: erratic changes possibly due to chaos or drastic change. Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles.

Simplified Population Change Curves © 2004 Brooks/Cole – Thomson Learning (3) Irregular (1) Stable Number of individuals (4) Cyclic (2) Irruptive Time

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)

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