Population Ecology

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

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

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

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

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

Density independent factors Weather events natural disasters

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

Human population growth See page human population reaches 1 billion in 130 years 2 billion in 30 years 3 billion in 15 years 4 billion in 12 years 5 billion in 12 years 6 billion

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

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

Communities of organisms Chp 46 Producers - autotrophs Consumers - heterotrophs primary and secondary Decomposers - heterotrophs

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)

Mutualism A symbiotic relationship both partners benefit –rhizobium bacteria and plants –pilot fish and sharks?

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

Parasitism Parasite and host pathogen - parasite that causes disease

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

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)

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 -