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2.1. SPECIES AND POPULATIONS (Knowledge and Understanding (Niches…
2.1. SPECIES AND POPULATIONS
Knowledge and Understanding
A species interacts with its abiotic and biotic environment, its niche is described by these interactions
Populations change and respond to interactions with the environment
Population -
group of organisms of the same species living in the same area at the same time - which are capable of interbreeding
All systems have a carrying capacity for a given species
Species
- a group of organisms sharing common characteristics that interbreed to produce fertile offspring
Habitat
- the environment in which a species normally lives
Niches
Fundamental niche: full range of conditions and resources in which a species could survive and reproduce
Realised niche: the actual conditions and resources in which a species exists due to biotic interactions
Niche -
particular set of abiotic and biotic conditions and resources to which an organism responds
Interactions should be understood in terms of influences each species has on the population dynamics of others and upon the carrying capacity of others' environment
Basics of ecology
Factors affecting population size
natality (BR)
mortality (DR)
migration - immigration and emigration
Many populations of different species (a community) may share the same habitat
No two species can inhabit the same ecological niche in the same place at the same time
Biotic factors in a niche
Every relationship the organism may have
Where it lives
How it responds to resources available, predators and competitors
How it alters these biotic factors
Abiotic factors
How much space there is
Availability of light, water etc.
Limiting factors
prevent a community, population or organism growing larger. Limiting factors will slow population growth as it approaches the carrying capacity of a system
Population interactions - termed biotic factors
Competition
Intraspecific - between members of the same species - when numbers of a population are small there is little competition between individuals for resources. As pop. grows so does competition until eventually the carrying capacity of the ecosystem is reach. Some species deal with competition by being terriorial
Intraspecific competition tends to stabilise population numbers - produces s shaped curve
Interspecific - individuals of different species - may lead to a balance in which both species share the same resource, other outcome is one species might out-compete the other - competitive exclusion
Competition reduces the carrying capacity for each competing species as the use the same reource(s)
Predation
one animal (predator) eats another (prey) - predation is the consumption of one organism by another
Herbivory
animal (herbivore) eating a green plant - some plants have defences e.g. thorns in cacti
Parasitism
Relationship between two species where one (parasite) lives in or on another (host) gaining food from it - normally parasites do not kill the host however high parasite population densities can lead to the hosts death
Mutualism
relation between two or more species when all benefit and none suffer - a form of symbiosis (living together)- other is parasitism and commensalism (one partner is helped and other is not significantly harmed) e.g. sea anemone and clownfish - clownfish feed anemone w their faeces and anemone protects clownfish because they sting other fish but do not affect the clownfish
Population changes
S curves
start with exponential growth - no limiting factors affect the growth at first - but above a certain pop size the growth rate slows down gradually ultimately resulting in a population of a constant size - numbers stabilise at the carrying capacity
J curves
'boom and bust' pattern - population grows exponentially at first then suddenly collapses - collapses are called diebacks. Often the population exceeds carrying capacity on a continuing basis before the collapse occurs (overshoot)
typical of microbes, invertebrates, fish, small mammals
S and J curves are idealised curves - in practice many limiting factors act on the same population resulting in population growth curve looking like a combination of both S and J
