Populations and Sustainability Flashcards
(a) Explain the significance of limiting factors in determining the final size of a population;
Any factor that prevents a population from increasing in size is a limiting factor. At any one time, there is usually just one factor limiting population growth, but different limiting factors come into play at different times. May be seasonal. Limiting factors include abiotic factors (light/water/space availability, temperature/chemical composition of their surroundings; non-living components of the ecosystem) or biotic factors (the living components/features of an ecosystem).
A habitat cannot support a population large than its carry capacity because of limiting factors which place a limit on population size.
For plants, limiting factors may include:
- Light availability
- Water availability
- Carbon dioxide availability
- Nutrient ion/mineral availability
- Temperature
- Infection by pathogens
- Absence of agent for cross-pollination
- Space availability (but another factor almost always becomes limiting before physical space)
- Intensity of competition for resources
- Effects of other species
For animals, limiting factors may include:
- Lack of food/prey
- Lack of water
- Lack of oxygen (likely only in aquatic habitats)
- Lack of suitable site for reproduction/egg-laying
- Temperature
- Infection by pathogens/parasites
- Lack of a mate at very low population density
- Lack of shelter
- Lack of space (many animals defend a territory, ensuring resources for reproduction)
- Intensity of competition for resources
- Effects of other species
- Predation
(b) Explain the meaning of the term carrying capacity;
The maximum population density/size of an organism that can be maintained/supported permanently in a particular habitat, determined by one or more density-dependent (these have a proportional increase/decrease in its effect as the population density rises or falls; density-independent factors are not related to population size) limiting factors: abiotic/biotic.
(c) Describe predator–prey relationships and their possible effects on the population sizes of both the predator and the prey;
- As the prey population increases, there’s more food available for predators, so the predator population increases too.
- As the predator population increases, more prey are eaten; so the prey population begins to fall.
- A decrease in prey population results in less food for the predators, fewer predators can survive, so their population crashes and decreases.
- With fewer predators, fewer prey are eaten, thus prey population increases again, and the cycle continues.
However, there are other factors involved, such as food availability for the prey; a population of prey may start to decline initially due to too many of them being around for the food available/changes in nutritive quality of food plants/reduction in breeding success at high population densities, with the decline in prey population then exacerbated and accelerated by predation from the predator.
(d) Explain, with examples, the terms interspecific and intraspecific competition;
Interspecific competition
Between individuals of different species. If both species occupy the same niche (way of life), the competitive exclusion principle applies (two species competing for the same resources cannot co-exist if other ecological factors remain constant; as soon as one species gains a slight advantage of the other, it will outcompete the other species to extinction in that ecosystem). It states that as a result of competition, two species will not occupy the same niche.
Competition between individuals of different species can affect both the population size and the distribution of a species in an ecosystem as no two species can occupy the same niche; if one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed; won’t be able to exist alongside the better adapted species. Compete for same resources; e.g. food and habitat; resources available to both decrease, both species limited by less food; thus less energy for growth + reproduction; population size lowers for both species.
E.g. Red vs. Grey squirrel
The red squirrel out-competes the grey in conifer woods, but the grey squirrel out-competes the red in woods with less than 75% conifers. The grey squirrel has a better chance of survival as it is larger and can store more fat over winter.
Intraspecific competition
Between individuals of the same species. Density-dependent (abiotic + biotic) factors limit population growth, and the individuals with adaptations best suited to the prevailing conditions will out-compete the less well adapted. A cause of natural selection.
If food supply becomes a limiting factor, the individuals best adapted to obtaining food will survive and reproduce, whereas those less well adapted will die out and fail to pass on their genes.
(e) Distinguish between the terms conservation and preservation;
Conservation is the protection and management of ecosystems so that the natural resources in them can be used without them running out; area can still be sustainably exploited, with the active management needed to maintain or increase biodiversity.
Preservation is the protection of ecosystems so they’re kept exactly as they are; protecting species by leaving their habitats untouched. E.g. creating a nature reserve
(f) Explain how the management of an ecosystem can provide resources in a sustainable way, with reference to timber production in a temperate country;
Sustainable management allows the same area to be exploited indefinitely:
- It does not result in loss of fertility (e.g. by soil erosion)
- The population that is exploited does not become extinct or decline seriously
- Biodiversity is maintained; the destruction of other species that share the habitat with the exploited species is avoided.
Examples of sustainable management of timber production include:
Selective felling; some mature trees, diseased trees and unwanted species are harvested, leaving other trees to develop and distribute seeds to fill the gaps created. This is more expensive than cutting all the trees on the site (clear felling).
Strip felling; small patches or strips of forest are cleared completely, leaving other patches untouched to cut many years later, after the first areas have regrown. Large areas are not felled at the same time, so loss of species and soil erosion are eroded.
Coppicing; trees are cut down, leaving stumps from which new shoots develop. These grow rapidly because they have a well developed root system. After a few years, the shoots are cut and yield poles, but not large logs. Coppicing can be repeated indefinitely. Small strips or patches are cut in different years providing a variety of habitats and so producing high biodiversity.
Only some species of tree can be coppiced; pines and firs do not develop new shoots from cut stumps, hazel and sweet chestnut however, do.
(g) Explain that conservation is a dynamic process involving management and reclamation;
Conservation is a dynamic process – conservation methods need to be adapted to the constant changes (caused both naturally and by humans) that occur within ecosystems. Maintaining biodiversity in dynamic ecosystems requires careful management to maintain a stable community, or even reclaim an ecosystem by reversing the effects of human activity, resorting ecosystems that have been damaged or destroyed so that they can be used again, e.g. restoring forests that have been cut down so they can be used again.
Conservation measures include:
- Protection of species; e.g. laws against hunting of the blue whale
- Protection of habitats; e.g. laws preventing the discharge of wastes into rivers
- Restoration/reclamation; e.g. erecting sea defences, preventing sand being blown off dunes
- Creating new habitats; e.g. digging ponds, planting new woodland
- Captive breeding of endangered species; e.g. breeding programs
- Prevention of succession; e.g. grazing/burning of heath or grassland
- National action; e.g. laws preventing destruction of bats and their roosts
- International action; e.g. Convention on International Trade in Endangered Species (CITES) treaty, preventing trade in products such as rhino horns.
- Raising the carrying capacity by providing extra food
- Moving individuals to enlarge populations, or encouraging natural dispersion of individuals between fragmented habitats by developing dispersal corridors of appropriate habitat
- Restricting dispersal of individuals by fencing
- Controlling predators and poachers
- Vaccinating individuals against disease
- Preserving habitats by preventing pollution or disruption, or intervening to restrict the progress of succession
(h) Discuss the economic, social and ethical reasons for conservation of biological resources;
Economic
- Drugs; natural environments are valuable sources of potentially beneficial resources
- Clothes
- Food
- Genetic diversity in wild strains of domesticated species may be needed in future for certain characteristics
- Natural predators of pests can acts as biological control agents
- Wild insect species pollinate crop plants
- Other organisms maintain water quality, protect soil and break down waste products
- There is also evidence that reduced biodiversity may cause reduced climatic stability
Social
- Ecotourism relies on biodiversity, as does recreation
Ethical
- Every species has a value in its own right, to live in the way they are adapted
- Every living thing has the right to survive
General:
- part of food chain / part of ecosystem / part of food web / scavengers
- have a right to existence / moral reason; ethical
- give pleasure / beautiful creatures; aesthetics; tourism
- ecotourism
- useful product / source of medicine / medical research;
- genetic resource
- prevents disease
- maintain/increase gene pool
Evolution has provided answers to many technological questions- the best aerodynamic shape in water, the best shape for a wing etc.
Natural ecosystems perform many processes that are of value to humans:
a) economic – growth of timber, food and fuel. Crop pollination and recycling wastes, detoxification. Clothing, drugs (e.g. morphine made from poppies)
b) ecological – regulation of the climate and atmosphere (photosynthesis removes CO2 and replaces it with O2; prevent habitat destruction), soil formation/fertilisation (couldn’t grow crops w/o soil if nutrient cycle was disrupted) and water purification/retention.
c) ethical – all living organisms have a right to live in the way they are adapted
d) aesthetic – we need the natural environment for our physical, emotional and intellectual health.
Medical: Studies have shown that patients recover more rapidly from stress and injury when they are exposed to pleasing natural environmental conditions. Maintenance of biodiversity to discover new drugs to cure currently incurable diseases.
(i) Outline, with examples, the effects of human activities on the animal and plant populations in the Galapagos Islands
In 1980 the population of the Galapagos Islands was 5000, and about 4000 tourists visited every year.
In 2005, the population was 28,000, and 100,000 tourists visited every year.
- Dramatic increase in population size has placed huge demand on water, energy and sanitation services
- More waste and pollution have been produce
- The demand for oil has increased
- 2001 oil spill had an adverse effect on marine and costal ecosystems
- Increased pollution, building and conversion of land for agriculture has caused destruction and fragmentation of habitats
- Species have been harvested faster than they could replenish themselves.
- Giant tortoises were taken to be eaten on long voyages
- Fishing for exotic species of fish has decimated the population
- Depletion of sea cucumbers has had a drastic effect on under-water ecology
- International market for Shark-fin has led to the deaths of around 150,000 sharks each year
- Humans have introduced many non-indigenous species
- The red quinine tree spread rapidly and outcompetes the native species. Its presence has changed the landscape from mostly low scrub and grassland to a closed canopy forest. Many native animals have lost their nesting sites
- Goats eat species unique to the islands, outcompete giant tortoises for grazing, trample on tortoise nesting sites, transform forests into grassland, causing soil erosion
- Cats hunt a number of indigenous species
