Population Ecology Flashcards
What is a population?
A group of organisms of the same species living in a particular area
What organisms have scientists used, typically, to study population growth?
They have studied bacteria grown in nutrient media in closed conditions (bacteria or conical flask)
What factors influence population growth?
Birth rate, death rate, immigration (moving into population) and emigration (leaving)
What are the 4 main stages of population growth?
Lag, Exponential, Stationary and Decline phases
Briefly describe the bacterial growth phases
-Lag-> very slow increase in numbers, bacteria activate genes and enzymes for nutrient assimilation
-Exponential-> exponential growth with no restrictions as resources are plentiful and bacteria are diving at max rate
-Stationary-> resources become limiting and toxins and wastes start to build up, birth rate and death rate are at or close to equilibrium
-Decline-> resources such as nutrients run out or toxins accumulate causing death rate to exceed birth rate, may lead to population crash
How might population growth differ in species other than bacteria?
Other organisms typically display something more like a sigmoidal or s-shaped growth curve (seen often when they colonise a new area) as conditions aren’t closed and the resources tend to be renewable rather than non-renewable, the curve stops at the stationary stage
What is the biotic potential of a population?
This is when a population is reproducing at its maximum rate under optimum environmental conditions, as seen during the exponential phase of
What is environmental resistance?
Refers to the environmental restrictions that prevent a population from achieving its biotic potential and max growth, it includes factors like lack of nutrients, waste build-up, competition, predation, disease and climatic factors
What are biotic and abiotic factors?
Biotic factors are factors due to other organisms, such as competition and predation
Abiotic factors are the non-living, physical factors such as nutrients, oxygen availability, light intensity, rainfall, temperature
What is the carrying capacity of a population?
This is the maximum number of a population that the ecosystem can support, and it is determined by the resource availability
Organisms such as protoctistans (phytoplankton) in the oceans have a J-shaped growth curve. Explain why
In spring time the temperature and light intensity are increasing, nutrient supply is abundant, and there are few herbivorous feeders, leading to a period of very rapid growth. This is followed in summer by a crash when nutrient supplies are exhausted and herbivores are increasing in number.
What is competition and explain the difference between the two types
Competition is when different organisms are competing for the same resource which is in short supply (limited resource)
Intraspecific-between members of the same species
Interspecific-between members of different species
What important principle did we learn about at AS, when we studied the investigation into competition between 2 species of paramecium?
The competitive exclusion principle- no 2 species can occupy the same ecological niche. One will always lose out (the least well adapted one)
Explain the typical predator-prey interactions
-As the number of prey organisms increases, there is more food available for predators, so their numbers increase. Thus predator peaks follow prey peaks.
-Prey numbers subsequently decrease, followed by a decrease in predators as food availability decreases. With less predation, prey numbers increase once more and the relationship continues in an oscillating manner, with similar lengths of cycles for predator and prey
-Predator numbers will always be lower than prey numbers (at equivalent points)
What is the equation for working out population growth?
Population growth= (births-deaths) + (immigration-emigration)
P= (B-D) + (I-E)
