Studying organisms in their environment Bio biosphere ecosystem community population organism organism biosphere

Populations Occupy niches in ecosystems Grow exponentially or logistically (carrying capacity) A group of the same kind of organisms living in the same place at the same time. EVOLVE! Allele frequencies can be described by the Hardy-Weinberg Equilibrium: p2 + 2pq + q2 = 1 Measured by random sampling Not realistic but, offers a standard to compare rates of evolution to – Null Hypothesis Will remain the same if no migration, no selection, random mating. No evolution

Life takes place in populations group of individuals of same species in same area at same time rely on same resources interact interbreed Population Ecology: What factors affect a population?

Population Size Changes to population size adding & removing individuals from a population birth death immigration emigration

Population growth rates Factors affecting population growth rate sex ratio how many females vs. males? generation time at what age do females reproduce? age structure how females at reproductive age in cohort?

Population growth change in population = births – deaths Exponential model (ideal conditions) dN = riN dt growth increasing at constant rate N = # of individuals r = rate of growth ri = intrinsic rate t = time d = rate of change every pair has 4 offspring every pair has 3 offspring intrinsic rate = maximum rate of growth

Exponential growth rate Characteristic of populations without limiting factors introduced to a new environment or rebounding from a catastrophe Whooping crane coming back from near extinction African elephant protected from hunting

Introduced species Non-native species kudzu transplanted populations grow exponentially in new area out-compete native species loss of natural controls lack of predators, parasites, competitors reduce diversity examples African honeybee gypsy moth zebra mussel purple loosestrife gypsy moth kudzu

Zebra musselssel reduces diversity ~2 months ecological & economic damage reduces diversity loss of food & nesting sites for animals economic damage

Purple loosestrife reduces diversity 1968 1978 reduces diversity loss of food & nesting sites for animals

Regulation of population size marking territory = competition Limiting factors density dependent competition: food, mates, nesting sites predators, parasites, pathogens density independent abiotic factors sunlight (energy) temperature rainfall swarming locusts competition for nesting sites

Logistic rate of growth Can populations continue to grow exponentially? Of course not! no natural controls K = carrying capacity effect of natural controls What happens as N approaches K?

Carrying capacity Time (years) 1915 1925 1935 1945 10 8 6 4 2 Number of breeding male fur seals (thousands) Maximum population size that environment can support with no degradation of habitat varies with changes in resources 500 400 300 200 100 20 10 30 50 40 60 Time (days) Number of cladocerans (per 200 ml) What’s going on with the plankton?

Human population growth Population of… China: 1.3 billion India: 1.1 billion Human population growth adding 82 million/year ~ 200,000 per day! Doubling times 250m  500m = y () 500m  1b = y () 1b  2b = 80y (1850–1930) 2b  4b = 75y (1930–1975) 20056 billion Significant advances in medicine through science and technology What factors have contributed to this exponential growth pattern? Industrial Revolution Is the human population reaching carrying capacity? Bubonic plague "Black Death" 1650500 million

Populations evolve Natural selection acts on individuals differential survival “survival of the fittest” differential reproductive success who bears more offspring Populations evolve genetic makeup of population changes over time favorable traits (greater fitness) become more common Presence of lactate dehydrogenase Mummichog

5 Agents of evolutionary change Mutation Gene Flow Non-random mating Genetic Drift Selection

Variation & natural selection Variation is the raw material for natural selection there have to be differences within population some individuals must be more fit than others

Where does Variation come from? Mean beak depth of parents (mm) Medium ground finch 8 9 10 11 1977 1980 1982 1984 Dry year Wet year Beak depth Beak depth of offspring (mm) Mutation random changes to DNA errors in mitosis & meiosis environmental damage Sex mixing of alleles recombination of alleles new arrangements in every offspring new combinations = new phenotypes spreads variation offspring inherit traits from parent

1. Mutation & Variation Mutation creates variation new mutations are constantly appearing Mutation changes DNA sequence changes amino acid sequence? changes protein? changes structure? changes function? changes in protein may change phenotype & therefore change fitness

2. Gene Flow Movement of individuals & alleles in & out of populations seed & pollen distribution by wind & insect migration of animals sub-populations may have different allele frequencies causes genetic mixing across regions reduce differences between populations