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

3. Populations 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: p 2 + 2pq + q 2 = 1 Will remain the same if no migration, no selection, random mating. No evolution Measured by random sampling Not realistic but, offers a standard to compare rates of evolution to – Null Hypothesis Grow exponentially or logistically (carrying capacity) Occupy niches in ecosystems

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

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

6. 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?

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

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

9. Introduced species Non-native species – 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 kudzu gypsy moth

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

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

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

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

14. 500 400 300 200 100 0 2001030504060 Time (days) Number of cladocerans (per 200 ml) Maximum population size that environment can support with no degradation of habitat – varies with changes in resources Time (years) 1915192519351945 10 8 6 4 2 0 Number of breeding male fur seals (thousands) Carrying capacity What ’ s going on with the plankton?

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

16. 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

17. 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

18. 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

19. Mean beak depth of parents (mm) Medium ground finch 8 891011 9 10 11 1977198019821984 Dry year Wet year Beak depth Beak depth of offspring (mm) Where does Variation come from? 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

20. 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

21. 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