B19 Flashcards
(24 cards)
ecology
the study of the inter-relationships between organisms and their environment
the environment
involves both abiotic (e.g. temp and rainfall) and biotic (e.g. competition and predation) factors
ecosystems
dynamic systems made of a community and all the non-living factors of its environment
within an ecosystem there are 2 main processes:
- the flow of energy through the system
- the cycling of elements within the system
population
a group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed
carrying capacity
the size of population that an ecosystem is able to support
the size of a population can vary as a result of…
- the effect of abiotic factors
- interaction between organisms e.g. inter/intraspecific competition and predation
community
all the populations of different species living and interacting in a particular place at the same time
habitat
the place in which an organism normally lives
- characterised by physical conditions and other types of organisms present
- within an ecosystem there are many habitats
- within each habitat there are smaller microhabitats with their own microclimate
ecological niche
describes how an organism fits into the environment
- refers to where an organism lives and what it does there
- includes the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population
- no two species occupy exactly the same niche
- this is the COMPETITIVE EXCLUSION PRINCIPLE
- some species may appear very similar, but their nesting habits or other aspects of their behaviour will be different, or they may show different levels of tolerance to environmental factors such as pollutants or a shortage of O2 or nitrates.
population growth equation
(births + immigration) - (deaths + emigration)
population size
number of individuals in a population
plotting growth curves
- where a population grows in size slowly over a period of time, it is possible to plot a graph of numbers in a population against time
- the growth of microorganisms is more rapid
- in these cases it is necessary to use a logarithmic scale to represent the number of microorganisms
- when the graph of log mircoorganism numbers is plotted against time, all points can be represented on the graph
population size- limiting factors
- MINERAL IONS are consumed as the population becomes larger
- the population ( in water) becomes so large that the organisms at the surface prevent LIGHT reaching those at deeper levels
- OTHER SPECIES are introduced and some of these species may use the original organisms as food, or compete for light/ minerals
- winter brings much lower temperatures and lower light intensity of shorter duration
- no population continues to grow indefinitely because certain factors limit growth, e.g. availability of food, light, water, oxygen, shelter and the accumulation of toxic waste, disease and predators
- each population’s carrying capacity can be sustained over a relatively long period, this is determined by these limiting factors
abiotic factors
*TEMPERATURE
- each species has a different optimum temperature
- the further away from this optimum, the fewer individuals in a population are able to survive and the smaller is the population that can be supported
- in plants and clod blooded animals, as temperatures fall below the optimum, the enzymes work more slowly and so their metabolic rate is reduced
- populations therefore have a smaller carrying capacity
- at temperatures above the optimum, the enzymes work less effectively as they denature
- in warm-blooded animals, they can maintain a relatively constant body temperature, regardless of the external temperature
- the further the temperature of the external environment from the optimum, the more energy the organism expends in trying to maintain their normal body temperature
- this leaves less energy for individual growth and so they mature more slowly and their reproductive rate slows, so the carrying capacity is reduced
*LIGHT
- the ultimate source of energy for ecosystems
- the rate of photosynthesis increases as light intensity increases
- the greater the rate of photosynthesis, the faster plants grow and the more spores/seeds they produce
- their carrying capacity is therefore potentially greater
- in turn the carrying capacity of animals that feeds on plants is potentially larger
*PH
- affects the action of enzymes
- each enzyme has an optimum pH at which it operates most effectively
- a population of organisms is larger when the appropriate pH exists
*WATER AND HUMIDITY
- where water is scarce, populations are small and consist only of organisms well adapted to living in dry conditions
- humidity affects transpiration rates in plants and the evaporation of water from the bodies of animals
when an abiotic factor is below the optimum for a population, fewer individuals are able to survive because their adaptations are not suited to the conditions
intraspecific competition
- between the same species
- it is the availability of resources e.g. food, water, breeding sites, that determine the size of a population
- availability of resources also affects the degree of competition between individuals, which results in a smaller population
interspecific competition
- between different species
- when populations of two species are in competition, one will normally have a competitive advantage over the other
- the population of this species will gradually increase, while the other will diminish
- if conditions remain the same, this will lead to the complete removal of one species (competitive exclusion principle)
competitive exclusion principle
when two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other-
- no two species can occupy the same niche indefinitely when resources are limiting
birth / death rates
- to show how a factor influences the size of a population, link to birth and death rates of individuals in the population
e.g. an increase in food supply does not necessarily mean there will be more individuals- it could just result in bigger individuals - a decrease in food could lead to individuals dying of starvation
- an increase in food means that more individuals are likely to survive and so there is an increased probability that they will produce offspring and the population will increase
competition
when 2 or more individuals share a resource that is insufficient to satisfy the requirements fully.
predator
an organism that feeds on another organism- their prey
how have predators evolved to become better at capturing prey
- faster movement
- more effective camouflage
- better means of detecting prey
how have prey become more adapted to avoiding predators
-better camouflage
- more protective features e.g. spines
- concealment behaviour
predation
predation occurs when one organism is consumed by another
- in nature, the area over which the population can tracel is great, and the variety of the environment is much more diverse
- in particular there are many more potential refuges
- some of the prey can escape predation because the more dispersed they are, the harder they are to find and catch
- therefore, although the prey population falls to a low level, it rarely becomes extinct
- evidence collected on predator-prey populations in a lab does not necessarily reflect what occurs in the wild
- it is difficult to obtain reliable data on natural populations, because it isn’t possible to count all the individuals in a natural population
- the size can only be estimated from sampling and surveys
effect of predator-prey relationships on population size
- predators eat their prey, reducing the prey population
- fewer prey available: predators are in greater competition with each other for the prey that are left
- the predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce
- with fewer predators left, fewer prey are eaten and so more survive and are able to reproduce
- the prey population therefore increases
- with more prey available as food, the predator population increases
- although predator-prey relationships are significant reasons for cyclic fluctuations in populations in populations, they are not the only reasons; disease and climatic factors are important
- these periodic population crashes are important in evolution as there is a selection pressure which means that those individuals who are able to escape predators/ withstand disease or adverse climates, are more likely to survive and reproduce
- the population therefore evolves to be better adapted to the prevailing conditions,
