24 Populations and Sustainability

Why do population sizes vary?

Abiotic Factors

Biotic Factors

What are some abiotic factors?

Light

Water

Space

Temperature

Chemical composition of surroundings

What happens when abiotic conditions are ideal for a species?

Organisms can grow fast and reproduce successfully.

e.g. when the temperature of a mammal's surroundings is the ideal temperature for metabolic reactions to take place, they don't have to use up as much energy maintaining their body temperature. This means more energy can be used for growth and reproduction.

What happens when abiotic conditions aren't ideal for a species?

Organisms can't grow as fast or reproduce as successfully.

e.g. when the temperature of a mammal's surroundngs is significantly lower or higher than their optimum body temperature, they have to use a lot of energy to maintain the right body temperature. This means less energy will be available for growth and reproduction.

What are the biotic factors affecting population size?

Interspecific competition

Intraspecific competition

Predation

What is interspecific competition?

When organisms of different species compete with each other for the same resources.

This can mean that the resources available to both populations are reduced and so both populations will be limited.

It can also affect the distribution of species. If two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.

What is intraspecific competition?

When organisms from the same species compete with each other for the same resources.

The population of a species increases when resources are plentiful. As the population increases, there'll be more organisms competing.

Eventually, resources become limiting - there isn't enough for all the organisms. The population then begins to decline.

A smaller population means there's less competition for space and food, which is better for growth and reproduction - so the population starts to grow again.

What is the maximum stable population size of a species that an ecosystem can support called?

The carrying capacity.

What is predation?

Where an organism (the predator) kills and eats another organism (the prey).

The population sizes of predators and prey are controlled by negative feedback.

What affect does predation have on population size?

As the prey population increases, there's more food for predators, so the predator population grows.

As the predator popuation increases, more prey is eaten - so the prey population begins to fall. This is an example of negative feedback. The prey population is restored to a more stable size.

This means there's less food for the predators, so their population decreases, and so on.

What other factors could be involved here?

Availability of food for the prey.

e.g. the prey population could initially begin to decline because there's too many of them for the amount of food available.

This is then accelerated by predation.

What are limiting factors?

They determine the carrying capacity of an ecosystem.

They can be abiotic or biotic.

What is conservation?

The protection and management of ecosystems so that the natural resources in them can be used without them running out.

It's a dynamic process - methods must be adapted to the constant changes (caused naturally or by humans) that occur within ecosystems.

What else can conservation involve?

The management of ecosystems - controlling how resources are used and replaced.

Reclamation - restoring ecosystems that have been damaged or destroyed so they can be used again.

What are the three main reasons conservation is important?

Economic reasons.

Social reasons.

Ethical reasons.

What are the economic reasons relating to conservation?

Ecosystems provide resources for lots of things that humans need.

These resources are economically important because they're traded on a local and global scale.

If the ecosystems aren't conserved, the resources that we use now, like drugs, clothes and food, will be lost, so there will be less trade in the future.

Tourism.

What are the social reasons relating to conservation?

Many ecosystems bring joy to lots of people because they're attractive to look at and people use them for activities, e.g. birdwatching and walking.

The species and habitats in the ecosystems may be lost if they aren't conserved, so future generations won't be able to use and enjoy them.

What are the ethical reasons relating to conservation?

Some people think we should conserve ecosystems simply because it's the right thing to do, e.g. most people think organisms have the right to exist, so they shouldn't become extinct as a result of human activity.

Some people think we have a moral responsibility to conserve ecosystems for future generations, so they can enjoy and use them.

What is preservation?

The protection of ecosystems so they're kept exactly as they are.

Nothing is removed from a preserved ecosystem and they're only used for activities that don't damage them.

e.g. Antarctica is a preserved ecosystem because it's protected from exploitation by humans - it's only used for limited tourism and scientific research, not mining or other industrial activities.

What does managing ecosystems in a sustainable way mean?

Enough resources are taken to meet the needs of people today, but without reducing the ability of people in the future to meet their own needs.

How can temperate woodland be sustainably managed?

Trees are cleared in strips or patches - woodland grows back more quickly in smaller areas between bits of existing woodland than it does in larger, open areas.

The cleared strips aren't too large or exposed - lots of soil erosion can occur on large areas of bare gorund.

Timber is sometimes harvested by coppicing - cutting down trees in a way that lets them grow back.

Native tree species tend to be planted in preference to non-native species. This si better for biodiversity because native species have long-established interactions with other native species.

Planted trees are attached to posts to provide support, and are grown in plastic tubes to stop them being eaten by grazing animals.

Trees aren't planted too close together - they won't compete with one another.

What is overfishing causing?

Fish stocks are declining.

Less fish for us to eat.

The ocean's food chains are affected.

Some species of fish may become extinct.

What is sustainable food production?

Having enough food without using resources faster than they renew.

How can fish stocks be conserved?

Using fishing quotas

Controlling mesh size of nets

Explain fishing quotas.

They are limits to the amount of certain fish species that fisherman are allowed to catch.

Scientists study different species and decide how big their populations need to be for them to maintain their numbers. Then they decide how many it's safe to catch.

International agreements are made that state the amount of fish each country can take, and where they're allowed to take them from.

What are the problems with fishing quotas?

Fish of the wrong species or size are still caught, but they end up being thrown back into the sea, often dead or dying, because the restrictions don't allow the fisherman to bring them ashore.

However, new rules are banning the discarding of fish like this and the whole catch will have to be brought ashore to be counted against the quota.

Explain controlling the mesh size of nets.

There are different limits to the mesh size of the fish net, depending on what's being fished.

This is to reduce the number of unwanted and discarded fish that are accidentally caught. Using a bigger mesh size will let the unwanted species escape.

It also means younger fish will slip through the net, allowing them to reach breeding age.

What are the problems with mesh size?

It can be difficult to determine exactly how big the mesh size should be in areas where several different fish species are fished for at the same time. And two nets, each of which meets regulations could be used one inside the other - effectively reducing the reported mesh size.

How is the Terai Arc being managed to reduce the conflict between conservation and preservation, and human needs?

The Terai Arc is an area of forest and grasslands on the border between Nepal and India.

A variety of plants and animals are found there, including endangered species like the Bengal Tiger. Nearly 7 million people also live here and depend on the forest's resources to survive.

Areas of this forest are being destroyed to make way for more housing - this destruction of habitat brings humans and animals in closer contact and increases conflict between the two. e.g. tigers can kill livestock and may be shot and killed.

The WWF has worked with local people to help balance their needs with conserving the forest and its wildlife. e.g. the charity has provided people with things like solar cooker and biogas generators, so they don't need to use wood from the forest as fuel. Farmers are encouraged to plant mint hedges around their crops to keep animals away.

How is the Maasai Mara being managed to reduce the conflict between conservation and preservation, and human needs?

National reserve in kenya. Large area of grassland, which is home to huge populations of wildebeest and zebra etc.

The Maasai people traditionally earn a living by raising livestock, such as cattle. This can bring them into conflict with conservations - e.g. overgrazing by livestock can destroy grassland.

Conservation trusts are working with the Maasai people to help them make money from their land through conservation and ecotourism projects rather than farming, and to farm in a sustainable way. So, the economic needs of the Maasai people are met, while still allowing the area to be conserved.

How are UK peat bogs being managed to reduce the conflict between conservation and preservation, and human needs?

Peat bogs are areas of wet peat. These peat bogs store water and carbon dioxide, and are home to lots of different plants and animals.

Farmers use peat bogs to graze sheep and deer. However, this can lead to conflict with conservationists because overgrazing causes loss of moss species, soil compaction (which increases water runoff down sheep paths, taking sediment with it) and general peat bog erosion.

Recent gov. funded programmes, like the Environmental Stewardship Scheme, have given farmers money to use the peat bogs in a sustainable way, e.g. lower the number of livestock that use the peat bogs, or remove livestock over winter.

What are the Galapagos Islands?

Small group of islands in the Pacific Ocean. Many rare species of plants and animals have evolved there and can't be found elsewhere.

Recently the number of inhabitants and tourists has increased considerably.

What are the effects of human activities on the Galapagos Islands?

Non-native animals introduced to the islands by humans eat some native species. This has caused a decrease in the populations of native species.

Non-native plants have also been introduced that compete with native plant species, causing a decrease to their populations.

What methods of control have been introduced to the Galapagos Islands?

Eradication programmes have removed wild goats from some of the smaller islands and wild dogs from the largest island. Quinine trees are kept in check using chemical herbicides and by uprooting young trees.

When people visit the Galapagos National Park, they are expected to follow a list of rules, which includes not bringing any live plants or animals, or moving them between the islands. People are also only allowed to visit in the company of a licensed guide.

What are the effects of human activities on Antarctica?

Visitors have caused pollution in the past by dumping sewage into the sea and leaving rubbish. Shipping accidents have lead to oil spills, which severely affect wildlife.

Hunting, whaling and fishing have all reduced wildlife populations in the area.

What methods of control have been introduced to Antarctica?

All waste apart from food waste and sewage must be taken away by ship for disposal in other countries. Many research stations now treat their sewage before releasing it.

Ships that use thick oil as fuel are now banned from Antarctic waters.

There are tourist restrictions, e.g. tourists are only allowed on land at certain locations for a few hours.

Hunting and whaling have been banned for some time now, although fishing continues.

What are the effects of human activities on the Lake District and Snowdonia?

Many of the visitors on the Lake District go walking. This leads to the erosion of foot paths and the loss of soil from hillsides. Soil that ends up in waterways and lakes can disturb the pH of the water, causing knock-on effects for wildlife. As the paths become harder to walk on, people can start to trample and destroy the sensitive vegetation either side of the paths.

Similar in Snowdonia. A lot of rain falls, which leads to the erosion of the paths. Walkers often trample the surrounding vegetation to avoid the floods.

What methods of control have been introduced to the Lake District and Snowdonia?

In the Lake District, conservation charities attempt to carry out regular repair and maintenance work on the paths and encourage the regrowth of damaged vegetation. Walkers are also educated about the importance of sticking to the paths.

In Snowdonia, volunteers have dug drains next to the paths to prevent them from flooding.