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)
In population growth, what are r-selected species?
-These are opportunistic, short lived species with a fast rate of reproduction (high “r”) who typically display the “boom and bust” or J-shaped growth curve as they reproduce so rapidly
-They tend to be small (eg bacteria and protoctistans) not food competitors, don’t display parental care, are not very specialised but can inhibit unstable or disturbed habitats and are good colonisers
In population growth, what are k-selected species?
-These are organisms who reproduce more slowly with a longer life cycle and fewer offspring and whose population tends to remain stable around the carrying capacity (or “k”)
-They tend to be larger, good competitors, display parental care and are highly specialised, so prefer stable, undisturbed habitats
What type of population interaction are both the predator-prey interactions and the grazing by herbivores?
They are +/- interactions (one gains and the other loses)
What is parasitism?
A +/- interaction in which an organism (the parasite) lives in or on another organism (the host) benefitting from it and causing it harm over a long period of
How is a parasite different to a predator?
The parasite lives IN/ON the host, it causes the host harm over a LONG PERIOD, the parasite is SMALLER than the host and it SELDOM KILLS it
What type of interaction is competition?
A -/- interaction as both species suffer (fewer and fewer individuals survive over time due to competition for resources). Eventually one species (better adapted) might eliminate the other
What is mutualism?
A +/+ interaction in which both partners benefit
Give 3 important examples of mutualism
- Lichens- these consist of algae and fungi (fungi provide shelter, water and minerals to algae; algae provide carbohydrates to the fungi through their ability to photosynthesise)
- Nitrogen fixing bacteria or legumes- the bacteria get carbohydrates from the photosynthesising plant and the plant gains amino acids from the bacteria
- Herbivorous animals have bacteria in their guts which help to digest cellulose via cellulases- therefore the cows are able to get nutrients from a wide range of food sources and the bacteria get a ready supply of food and an optimum temperature for metabolism
What is biological control?
Is is deliberately introducing an organism ( a predator, a competitor, a parasite or a pathogen) that will cause harm to a pest organism
What is a pest?
A pest species is one which damages a commercial or valuable crop, causing economic damage
What sort of problems do chemical pesticides cause?
-Many are broad spectrum which means that they kill beneficial organisms such as predators of the pest, as well as the pest
-This leads to pest resurgence, whereby pest numbers actually rise higher than before the pesticide was used
What does effective biological control aim to do?
It aims to bring pest numbers to be,ow the threshold level of economic damage by allowing the predator to integrate naturally in sustainable numbers
What are the advantages of biological control?
-No chemical damage or bioaccumulation in food chains
-Pest resurgence is unlikely
-Pest resistance is unlikely
-Cheaper due to no little additional action needed
What are the limitations of biological control?
-Pest is not totally eliminated
-It only works well if the biological control organism adapts well to the ecosystem it is introduced into
-The biological control organism must not out-compete non-target native species
