Population Ecology

1. Population Ecology

2. Ecology is the study of interactions among organisms and their environment • Not concerned with individuals • Populations - same area, same time • Population ecology - looks at the dynamics of populations that are similar between species

3. Population density - number of individuals of a given species in a specific area at a given time • Range - geographic area or limit of a population • Dispersion - frequency or patterns of individuals within a range: • uniform • random • clumped

4. Population change • Growth rate = births - deaths +immigration - emigration • Doubling rate (time it takes for a population to double) = 0.7/growth rate (see page 911) • Biotic potential = maximum rate of population growth given ideal circumstances

5. Limits on growth • Environmental resistance - combination of the limiting factors and effects • Limiting Factors - any resource or requirement that acts to limit population when in short supply • Carrying capacity (K) - the greatest population that can be maintained indefinitely by a given system or place

6. Density dependent factors • As population increases the rate of growth is slowed by density dependent factors either by increasing the death rate or decreasing the birth rate • predation, disease, intraspecifc (within a species) competition and interspecific competition

7. Density independent factors • Weather events • natural disasters

8. Survival tactics - reproduction • r strategies - (r=growth rate) - small body size, large brood, short life span, may be opportunistic and found in disturbed or variable environments • K strategies - (K=carrying capacity) - large body small brood, long life, care for young, constant or stable environments

9. Human population growth • See page 45-9 • 1800 human population reaches 1 billion • 1930 - in 130 years 2 billion • 1960 - in 30 years 3 billion • 1975 - in 15 years 4 billion • 1987 - in 12 years 5 billion • 1999 - in 12 years 6 billion

10. What are the density dependent limits to growth acting on human population?

11. Demographic transition • Preindustrial stage - high birth and death rates - slow population growth • transitional stage - lower death rate but birth rate remains high - rapid population growth • industrial stage - birth rate declines - rate of growth slows • post industrial stage - low birth and death rates

12. Communities of organismsChp 46 • Producers - autotrophs • Consumers - heterotrophs • primary and secondary • Decomposers - heterotrophs

13. No organism lives in isolation. Every living thing is part of a community. • Predation - pursuit and ambush • Defenses - camoflage, chemical defense, mimicry - (batesian mimicry or mullerian mimicry)

14. Mutualism • A symbiotic relationship • both partners benefit • rhizobium bacteria and plants • pilot fish and sharks?

15. Commensalism • One benefits , the other is neither harmed nor helped • epiphytes • sea ducks and sting rays

16. Parasitism • Parasite and host • pathogen - parasite that causes disease

17. Niche • The ecological role of an organism is its niche • fundamental niche- potential niche • realized niche- actual • interspecific competition leads to competitive exclusion - absolute overlap cannot exist in nature

18. Diversity in communities • Isolated or places with harsh environments have less diversity • edge effect - diversity is usually greatest at the margins • old communities (tropical rainforests) tend to be more diverse than new communities (Canadian shield, artic)

19. Succession • Primary succession - change in species composition over time in a habitat not previously inhabited by organisms • Pioneer community - first community to appear • Secondary succession - change in species composition over time in a habitat already modified by previous organisms • Climax community -