I. What is a Population? Individuals of a species that live in one place at one time. Individuals of a species that live in one place at one time. A. Characteristics of Populations: Will grow over time Will grow over time Will ultimately be limited by lack of resources Will ultimately be limited by lack of resources Population size will change in response to the environment Population size will change in response to the environment

II. Key Features of Population A. Population Size: The number of individuals in a population Size will effect the populations ability to survive SMALL Populations are more prone to extinctions and are impacted more by random events and inbreeding

B. Population Density The number of individuals that live in an area at one time

C. Dispersion – The way the individuals are arranged in space Clumped Elephants ** MOST COMMON SPATIAL PATTERN IN NATURE (GO TO THE RESOURCES) Random (dandelions) Uniform (creosote bush)

III. Population Growth Rates Billions of people ? ? ? million years Hunting and gathering Black Death–the Plague Time Industrial revolution Agricultural revolution B.C.A.D. Simple population growth models are described as the difference between the birth rate and the death rate within a population.

A. Exponential Growth: Observed in populations with few or no resource limitations. Starts slow and increases “J-shaped curve” Often described in terms of…

1. Biotic Potential: How large a population could grow to if there were unlimited resources 2. Environmental Resistance: All of the living and non-living factors working to hold a population size down. Populations typically can’t grow exponentially forever.

3. Carrying Capacity “k” Number of individuals of a given species that can be sustained in a given space indefinitely Determined by biotic potential and environmental resistance working against each other Number of sheep (millions)

What if we exceed the Carrying Capacity? The population can go above “k” for a short period of time The population will fall to recover If the recovery is too severe it will result in a CRASH or DIEBACK Result of REPRODUCTIVE LAG TIME

Reindeer in Alaska Fig. 9.6, p ,000 1,500 Number of reindeer Year 1,

B. Logistic Growth Model Exponential at first… Exponential at first… Slowing as the population encounters environmental resistance Slowing as the population encounters environmental resistance “S- shaped curve” “S- shaped curve” “K” Time (t) Population size (N)

IV.Factors that Influence Populations A. Density-Independent Population Controls: Affect a population size regardless of the density Flood, hurricanes, drought, fire, habitat destruction, pesticide spraying

B. Density-Dependent Population Controls: Greater effect as density increases Competition, predation, parasitism and disease

V. Growth Patterns A. r-selected species A. r-selected species (Opportunists) -Grow exponentially when optimal conditions -Reproduce early and put most of their energy into it -Large litters -Reach reproductive age early -Short generation times Little or no care to the offspring -Reproduce quickly when a disturbance opens up a new niche -Often get displaced by a more competitive species

B. k-Selected Species B. k-Selected Species (Competitor) -Show slow growth/stay near carrying capacity -Put little energy into reproduction -Reproduce late in life -Few offspring -Long generations -Put energy into protection and nurturing -Display logistical growth -Thrive best in constant environments

Which graph represents a k-selected and which one represents an r-selected population?