OCR Biology A - 6.3.2 - Population and Sustainability
A population growth curve has three stages: slow growth as numbers are small, rapid growth when resources are abundant and reproduction exceeds death, and a stable phase where population size levels off as it reaches the carrying capacity of the environment.
Stages on population graph
Slow growth
Rapid growth - resources plentiful, reproductive rate > mortality rate
Stable state (no growth) - mortality = reproduction
Cannot support a larger pop. due to carrying capacity, small fluctuations
Key Terms
Stages on population graph
Slow growth
Rapid growth - resources plentiful, reproductive rate > mortality rate
Stable state (no growth) - mortality = reproducti...
Populations can
Remain stable
Rise or fall suddenly
Oscillate up and down w. the reg. pattern
Types of limiting factors
Density dependent
Density independent
Density dependent
Factors that affect pop. the more they increase in size e.g resources, predators, intra and inter spp comp.
These limiting factors place the ...
Density independent
Factors that affect the the same proportion of the population regardless of size
Types of strategists
k and r
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| Term | Definition |
|---|---|
Stages on population graph | Slow growth Rapid growth - resources plentiful, reproductive rate > mortality rate Stable state (no growth) - mortality = reproduction Cannot support a larger pop. due to carrying capacity, small fluctuations |
Populations can | Remain stable Rise or fall suddenly Oscillate up and down w. the reg. pattern |
Types of limiting factors | Density dependent Density independent |
Density dependent | Factors that affect pop. the more they increase in size e.g resources, predators, intra and inter spp comp. These limiting factors place the carrying capacity on population size |
Density independent | Factors that affect the the same proportion of the population regardless of size |
Types of strategists | k and r |
K selection | Offspring have a high prob of survival Heavy parental care and nurturing Larger organisms Much lower reproductive rate Young are altricial, longer lifespans and have overlapping generations |
Altricial | Born in an undeveloped state and requiring care and feeding by the parents |
R selection | Produce many low effort organisms Species grow rapidly Found in less competitive and low quality environments Young are precocial High of mortality so start reproducing earlier Non overlapping generations, shorter lifespans Boom and bust (cyclical) |
Precocial | Born in an advanced state and able to feed itself almost immediately |
Predator prey interactions | When predator pop increases, more prey eaten Prey pop decreases, less food available for predator s W/ less food, fewer predators survive so their pop. decreases W/ fewer predators, fewer prey are eaten so their pop. increases More prey = more food, predator pop. increases Two populations are in eqm and stable due to -ve feedback |
When does competition occur | When there are not enough resources to satisfy all of the organisms that depend on them |
How does intraspp comp affect population | Population drops –> comp. reduces –> pop. increases –> pop. drops (oscillates) |
Examples of interspp comp. affecting population | Red and grey squirrels - Invasive species May leads to extinction of one species Greater specialisation to avoid competition Change in distribution of the species |
Where does invasive species have a largest effect | Islands |
Competitive exclusion principle | 2 competitive species cannot coexist at the same population level esp if ones staring population is higher than the other |
Preservation | Keeping habitats/species as they are now (assuming they are currently undisturbed) Focuses on eliminating any human effects on ecosystems |
Conservation | Active management of ecosystems by humans to maintain biodiversity Involves management of ecosystem so that natural resources can be used sustainably and reclamation |
Reclamation | Restoring ecosystems that have been damaged/destroyed |
Threats to biodiversity | Over-exploitation of ecosystems by humans Habitat disruption and fragmentation Intro of invasive species by humans that outcompete native species to extinction |
Potential management strategies | Raise carrying capacity by increasing nutrients Move individuals to enlarge pop Encourage natural dispersion using dispersion corridors between fragmented habitats Fencing Controlling predators and poachers Vaccinate individuals Prevent pollution/disruption Intervene to restrict succession |
Ethical reasons to conserve | Moral responsibility All organisms have a right to live Every species has value in and of itself |
Why does interspp competition have diff effects in the wild | Species may migrate Other biotic and abiotic effects on the organism Availability of resources vary Organisms may not have exactly overlapping niches |
Small scale timber production | Coppicing Pollarding |
Sustainable management | Carrying out processes indefinitely w/out damaging the ecosystem |
Coppicing | Stem of deciduous tree is cut close to ground New shoots grow from the cut surface Mature into narrower stems Happens cyclically |
What is coppicing used for | Fencing Firewood Furniture |
Pollarding | Sim technique to coppicing | Only done higher up so that the animals cant eat the new shoots |
Negative of small scale timber production | Labour intensive |
Rotational coppcing | Divide wood into sections | Cut one each year |
Why is rotational copppicing good for diversity | Light is still able to reach forest floor as tress never grow tall enough --> increasing diversity of species Can control succession (deflection - plagioclimax) |
Large scale timber production | Clear felling | Selective cutting |
Clear felling | Felling all the trees in one area destroying habitats on a large scale |
Drawbacks of clear felling | Decreases soil mineral level Leaves soil susceptible to erosion Takes 50-100 years of succession Trees bind soil Trees remove water from soil and stops it from being washed away Trees maintain nutrient levels through their roles in the carbon and nitrogen cycle (decomposition) |
Selective cutting | Only cutting down the largest, most valuable trees |
How is tree growth encouraged for selective cutting | Controlling pests and pathogens Only planting species where they will grow well Position tress at optimum distance to decrease comp |
Aims of sustainability | Preserve the environment Ensure resources are available for future generations Allow all humans to live comfortably Enable LEDCs to develop |
Modern sustainable forestry | Any tree harvested is replaced by another (naturally or planted) Forest must maintain its ecological function Local people must benefit from the forest |
Main principles of fisheries | Take place at a level that allows it to continue indefinitely (ideally carrying capacity and excess are harvested) Must maintain structure, productivity, function and diversity of the ecosystem Must adapt to changes in circumstances and comply w. local, national and international regulation |
Strategies put in place for fisheries | Large mesh sizes so only mature fish are caught Limiting recreational/ commercial fishing to certain times of the year EU common fisheries policy - Fishing quotas limiting no. of certain fish and where they can be caught |
Aquaculture | Farming fish Restricts impacts on oceanic fish value Allows susceptible fish species numbers to recover But decreases genetic biodiversity |
Why do fish numbers fall | Too few adult fish left to breed and maintain fish numbers |
Scramble competition | Relies on all individuals finding food and nest sites by chance this allows natural selection as some may be better adapted than others |
Dominance hierarchy | Strongest, most dominant individuals breed and pass on their alleles - if there's only 1 dominant individual there is likely to be less variation in the next gen. |
Why is preservation not enough to maintain biodiversity | Preservation only keeps the environment as it is If the ecosystem has already decreased preservation doesn't prevent further loss Takes active intervention |
Masai Mara region | National reserve in Kenya Combined needs for locals to run farms w/ larger land owner who use land to encourage conservation and generate income (ecotourism) |
Terai region | Home to Bengal Tiger (endangered) Forest is under pressure due to increased agriculture and grazing Comm forestry initiatives allow locals to exploit but also adopt responsibility Marketing products made for forests also generates income |
Peat bogs | Peat takes 1000's of years to accumulate Ideal for Sphagum moss - feeding and stopping off points for migrating birds Local level schemes aim to restore certain peat bogs and end commercial use |
Human activities affecting the Galapagos | Fishing and whaling have upset the marine ecosystem Intro of new species e.g. goats (eat vegetation), rodents (damage eggs of natives), dogs and cats (chase and eat native) Tourism Scientific research Increasing pop. |
Strategies to maintain the Galapagos | Searching boats for foreign species Using natural predators Culling feral goats Educating Captive breeding for tortoises Galapagos Marine Reserve |
Antartica | Overfishing of krill (keystone species) Moinitor catch size Whales protected by marine reseves Sea birds protected by night fishing and during the non-breeding seasons |
Measuring distribution | Line or belt transects (systematic sampling) |
Measuring plant abundance | Randomly placed quadrats | No. of individuals in sample / Area of sample |
Measuring animal abundance | Capture, mark, release, recapture (all occurs in orig. sample area) (no. in first sample * no in 2nd sample) / no. of recaptured marked individua |