CH5 Populations Flashcards
What are the factors that affect all the organisms living in an ecosystem.
- The intensity of energy flowing through the ecosystem varies.
- Biological cycles, such as the nitrogen cycle, vary the mineral availability
- Habitats change over time as succession occurs
- New species arrive and some species are no longer present
What is the size of a population at a particular time determined by?
- Birth rate (hatching, reproduction by binary fission and all other ways organisms increase their numbers
- Death rate
- Immigration
- Emigration
What are fugitive species?
Species that are poor at competition: instead they rely on a large capacity for reproduction and dispersal to increase numbers. They invade a new environment rapidly, e.g. algae colonizing bare rock and rose bay willow herb colonising soil cleared by fire
What are equilibrium species?
Species control their population by competition within a stable habitat. Their usual pattern of growth is a sigmoid (s-shaped) curve called the one-step growth curve. Seen for example when bacteria are put into nutrient solution or when rabbits are newly introduced to an island.
What is the lag phase?
A period of slow growth. A period of adaptation or preparation for growth, with intense metabolic activity, especially enzyme synthesis
What is the exponential phase?
When numbers increase as long as there are no limiting factors. More individuals available for growth. Population doubles per unit time.
What are the environmental resistance factors that slow down growth?
- Less food available
- The concentration of waste products becomes increasingly toxic
- There is not enough space or nesting sites
what are the factors that limit growth?
- available food
- overcrowding
- competition
- accumulation of toxic waste
what are some biotic factors that limit growth?
- predation
- parasitism and disease because increased population density allows infection to spread more rapidly
- competition
name some abiotic factors that limit growth?
temperature and light intensity
what is the stationary phase?
occurs when birth rate is equal to death rate and the population reaches its carrying capacity
what is the carrying capacity?
the maximum number of individuals that an area can support
what is the death phase?
when the factors that slow population growth at the end of the log phase become more significant population decreases
how are the populations of predator and prey regulated?
negative feedback (prey increase so predator increase meaning that prey decrease until there aren’t enough prey to support the predators so predators decrease).
why is a log scale used for population graphs of bacteria?
the population increase is very large
what are density dependent factors?
environmental factors that have more effect if the population in a given area is larger (as they affect a greater proportion of the population).
Name some density dependent factors?
they are biotic factors and include:
disease, parasitism and depletion of food supply
why do density dependent factors have more effect depending on the density of the population?
if population s denser, parasites are transmitted more efficiently and a greater proportion of individuals are affected.
also if prey density is higher, predators encounter them more often and so predator population increases.
what are density independent factors?
they are abiotic factors and there effect is the same regardless of the size of the population.
how does negative feedback work?
if the population rises above the carrying capacity, a density dependent factor increases mortality or reduces breeding to such an extent that the population declines.
if the population falls below the carrying capacity, environmental resistance is temporarily relieved so that the population rises again.
how is animal abundance assessed?
- capture-mark-recapture using the Lincoln index calculation
- kick sampling in a stream and counting aquatic invertebrates
