 Population  group of individuals of same species in same general area  rely on same resources  interact  interbreed

Populations repond to variation on a scale… or “grain”. Grain be either: Spatial (size/location) or Temporal (daily vs seasonal) Course Grained environment: Patches are large ; organism can select Fine Grained Environment: Patches are small ; organism cannot select.

Changes to population size  Adding & removing individuals from a population  birth  death  immigration  emigration

Demography  Factors that affect growth & decline of populations.  vital statistics & how they change over time Life table What does this tell you about the population?

Factors that affect birth/death rates: AGE STRUCTURE: relative numbers of individuals at each age. In general, older populations grow more slowly than younger populations. GENERATION TIME: span of time between birth and first reproductive event. Often directly related to body size. Other factors being equal, shorter generation time = faster population growth SEX RATIO: proportion of each sex in population. number of females more significant except for monogamous species. CLUTCH SIZE: number of offspring per episode. Smaller clutches usually larger kids. Tends to increase with latitude. Trade off between number & quality.

Survivorship curves  What does this tell about survival & strategy of a species?

Population growth change in population = births – deaths dN = rmaxN dt N = # of individuals r = rate of growth t = time period maximum rate = intrinsic rate of increase

Exponential growth rate  Characteristic of populations introduced to a new environment or rebounding from a catastrophe. Whooping crane coming back from near extinction African elephant protected from hunting

Carrying Capacity  Carrying Capacity (K)  Can populations continue grow exponentially?  Of course NOT! What sets limit?  Carrying Capacity (K) maximum population size that environment can support with no degradation of habitat.  not fixed; varies with changes in resources

Logistic model of growth Or…. Let’s just practice this on the board.

Life history traits r-selection = maximize reproductive success Populations fluctuate, shorter maturation time/lifespan, higher mortality rates, lager clutch sizes, less parental care, reproductive events. K-selection = density dependent Populations remain more constant, (near carrying capacity). Characteristics opposite those of r-selected. Iteroparity- life history in which adults produce offspring over many years. Semelparity- life history in which adults have only a single reproductive opportunity to produce one large number of offspring.

Trade offs Principle of Allocation: Number & size of offspring vs. survival of offspring or parent Principle of Allocation: -Natural Selection has resulted in different budgeting strategies for each organism’s limited amount of energy.

Regulation of population size  Limiting factors  density independent  environmental disturbances  density dependent  food supply  competition  predators  Population cycles  population fluctuations ocean currents & cannibalism

Predator – prey interactions  Population cycles

Human population http://www.npr.org/2011/10/31/141816460/visualizing-how-a-population-grows-to-7-billion?ps=cprs

Total population (in billions) Annual increase (in millions) Figure 36.9a 100 10 Population increase 80 8 Total population (in billions) Annual increase (in millions) 60 6 40 4 Total population size 20 2 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050 Year Adapted from The World at Six Billion, United Nations Publications (1999).

Age structure  Relative number of individuals of each age What do the data imply about population growth in these countries?

Impact: Ecological Footprint youtube Is the human population near carrying capacity? Based on land & water area appropriated to produce all resources it consumes & to absorb all wastes it generates Is the human population near carrying capacity? 2008 = ~6.5 billion K = 10–15 billion?