Populations
- 1. Populations
- 2. Population • Group of individuals of the same species occupying a common geographical area (a species is an interbreeding group of organisms that produces fertile offspring). – Same species, same place, same time!
- 3. Factors affecting Population • G.1.1 Outline the factors that affect the distribution of plant species, including temperature, water, light, soil pH, salinity and mineral nutrients. • G.1.2 Explain the factors that affect the distribution of animal species, including temperature, water, breeding sites, food supply and territory.
- 4. Population Dynamics • Natality – offspring are produced and added to the population (birth) • Mortality – individuals die and are lost from the population (death) • Immigration – individuals move into the area from somewhere else and add to the population • Emigration – individuals move out of the area and are lost from the population
- 5. Population Dynamics ∀∆ = N + I – M – E • In closed populations: ∆ = N – M • In English: Change = Births + Newcomers – Deaths – Exiters
- 6. Populations 5.3.2: Draw a graph showing the sigmoid (S-shaped) population growth curve. 5.3.3: Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.
- 7. Exponential Phase • Population increases exponentially because the natality rate is higher than the mortality rate. • This is because there is an abundance of food, and disease and predators are rare.
- 8. Transitional Phase • Difference between natality and mortality rates are not as great, but natality is still higher so population continues to grow, but at a slower rate. • Food is no longer as abundant due to the increase in the population size. May also be increase predation and disease.
- 9. Plateau Phase • Natality and mortality are equal so the population size stays constant. • Limiting Factors (5.3.4): – shortage of food or other resources – increase in predators – more diseases or parasites • If a population is limited, then it has reached its carrying capacity
- 11. Other Population Curves Growth curve for bacteria bacteria # time • Boom and bust
- 12. Factors Limiting the Growth of Natural Populations • All populations have a limit for exponential growth biotic potential (intrinsic rate of increase), r, under perfect conditions • Dependent on - # offspring/birth, capacity for survival, procreation rate, maturity • Since population is mainly affected by B-D, the factors that limit growth either birth rate or death rate • Abiotic factors – blizzards, hurricanes, floods (weather) – density independent regulation (death rate is independent of the population) • Biotic factors – predators, competitors, parasites – density dependent regulation (the proportion of individuals that die will depend on the size of the population – the birth rate and death rate are affected by the size of the population)
- 13. Survivorship Patterns (r- and K-) • r- (small letter, small creatures) • K- (large letter, large creatures)
- 14. r- selected • r-selected populations (small letter – small creatures) • variable, unpredictable climate ability to adapt • density independent factors mortality • lots of offspring • high juvenile mortality • population below carrying capacity • low level of competition • early development, reproduction, small body size, high reproductive capacity, reproduce only one, many offspring • short life-span (less than one year) • little/no parental care
- 15. K- selected • K-selected populations (capital letter – large creatures) • offspring’s survival depends on ability to obtain limited resources – produce a few highly competitive offspring (many young die if climate changes drastically) • fairly constant/predictable offspring • density-dependent mortality • low juvenile mortality • fairly constant population – at/near carrying capacity • high levels of competition • slow development, greater competitive ability, large body size, delayed & repeated reproduction, fewer, larger offspring • life-span longer