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6.3.2 Populatons and Sustainability (Sustainable Management (timber…
6.3.2 Populatons and Sustainability
Factors Determining Size of Population
limiting factor: the factor whose magnitude slows down the rate of a natural process
density dependant: factor influences population more strongly as population gets bigger/smaller e.g. availability of resources, disease
density independent: factor affects population equally irrespective of size e.g. temperature
carrying capacity: maximum population size that can be maintained over a period in a particular habitat
Interactions Between Populations
predator-prey relationships
1) predator population increase, more prey eaten
2) prey population decrease, predators have less food
3) predator population decrease as they have less food
4) prey population increase as there are fewer predators
5) predator population increase, cycle begins again
interspecific competition: competition between individuals of different species
more overlap in species' niches = more competition
two species cannot occupy the same niche, so one is either extinct from the population, or adapts a different niche
intraspecific competition: competition between individuals of the same species
best adapted individuals survive and reproduce, others die
population increase, competition increase, population drop
population decrease, competition decrease, population rise
competition: when resources are not present in adequate amounts to satisfy needs of all organisms present
Conservation vs Preservation
economic reasons:
valuable food source
discover new drugs
biological pest control agents
pollination
climatic stability
social
ecotourism
aesthetic
ethical reasons:
every species has value; human responsibility to fix problems
preservation: maintenance of habitats and ecosystems in their present conditions, minimising human impact
conservation: maintenance of biodiversity, including diversity between species, genetic diversity between species, and maintenance of a variety of habitats and ecosystems
threats: overexploitation (e.g. overfishing), habitat disruption and fragmentation (e.g. urbanisation, human population increase), introduction of non-native species
Sustainable Management
timber production
small scale: coppicing and pollarding
large scale: clear felling, sustainable forestry; when tree is cut down another must be planted, control pests and pathogens, position trees optimum distance apart
fishing
no overfishing
fishing quotas
raise carrying capacity by providing extra food
move individuals to enlarge population
restrict dispersal of individuals by fencing
control predators and poachers
vaccinate individuals against disease
prevent pollution or disruption
Strategists: two ends of a continuum of strategies adopted by living things
k-Strategists: species whos population size is determined by carrying capacity
limiting factors have increasingly more significant effect as population size get closer to the carrying capacity
population size gradually level out
e.g. birds, humans, mammals, large plants
characteristics: low reproductive rate, slow development, late reproductive age, long lifespan, large body mass
r-Strategists: population size increases so quickly that it exceeds carrying capacity before limiting factors have an effect
run out of resources, so species die due to buildup of waste, lack of space; boom and bust
e.g. mice, insects, spiders, weeds
characteristics: high reproductive rate, quick development, young reproductive age, short life span, small body mass
population size increase quick and go back down
Sammer Sheikh