F215 Module 3 Ecosystems and Sustainability

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Definitions

Ecosystem --> An environment consisting of all living things, and the interrelationships. They are dynamic - constantly changing.

Habitat --> The place where an organism lives.

Population --> All organisms of the same species living in the same population, can interbreed.

Niche --> The role a species plays in its ecosystem.

Producers --> Plants - they fix energy from the sun and supply energy to all consumers.

Consumers --> Eat plants (or animals) at the trophic level below them.

Decomposers --> Feed saprotrophically, by secreting enzymes to digest the dead and waste material into small molecules, which are absorbed and respired or stored.

Trophic level --> The level at which an organism feeds. Energy is lost at each trophic level - respiration, energy stored in the dead/waste/inedible parts of organisms.

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Pyramids

Numbers

A bar represents the number of organisms at each trophic level.

It does not measure the efficiency of energy transfer between each level.

Biomass

A bar represents the dry mass of organisms at that trophic level.

It gives no indication of how much energy each species releases per gram.

Energy

Organisms are burnt to find the energy released per gram.

It only gives a snapshot of the ecosystem at one moment in time.

Instead, productivity is measured - the rate at which energy passes through each trophic level, measured in MJ/m^2/year.

NPP = GPP - energy lost through respiration

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Improving productivity

Primary

Light levels early planting, light banks

Water levels drought-resistant plants are bred

Temperature greenhouses, early planting

Nutrients crop rotation, including a nitrogen fixing plant

Secondary

Harvesting younger animals more energy invested in growth

Steroids Improve growth - banned in the UK

Selective breeding gives more desirable animals

Antibiotics prevent energy loss to pathogens and parasites

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Succession

Primary succession --> Development of a community from bare ground.

Pioneer community small plants (e.g algae and lichen) are able to grow on bare rock.

Succession rock erosion and a buildup of dead organisms provide soil for larger plants (e.g mosses/ferns) to replace the pioneer community.

Climax community succession continues in the same way until a stable community is reached.

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Factors affecting population size

Carrying capacity --> The maximum population size that can be maintained over a period of time in a particular habitat. It may go up (e.g increased food supply) or down (e.g colder weather).

R strategists - boom and bust

These populations grow very quickly after good conditions (e.g desert plants after rain), spread their seeds, then die. This is typical of organisms with fast growth rates in harsh environments. They take advantage of the environment when it is most suited to them.

K strategists - longterm, stable population

Long-lived organisms with a slower growth rate and strategies for surviving in less favourable conditions. Limiting factors limit the population size, which oscillates around the carrying capacity.

Lag phase - few individuals acclimatising to their environment. Growth rate slow.

Exponential phase - plentiful resources and good conditions increase the growth rate.

Stationary phase - the population reaches carrying capacity. Rate of growth/rate is equal.

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Competition

When resources are not adequate to satisfy the needs of all the dependent individuals.

Intraspecific

Between members of the same species.

Occurs in the stationary phase, when the population is stable.

Interspecific

Between different species

The competitive exclusion principle applies - two species with exactly the same niche cannot survive in the same habitat. One will outcompete the other.

Conservation --> The maintenance of biodiversity, including the maintenance of species richness, species variation, habitat variation

Sustainable management --> Balancing human needs with conservation. Finding techniques to harvest the land, while conserving the ecosystem.

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Managing Timber Production

Small scale

Coppicing - cutting a decidious tree close to the ground. It will grow many shoots.

Pollarding - like coppicing, but higher up, so deer can't eat the growing shoots.

Large scale

Clearfelling - cutting all trees down in an area. Causes soil erosion and runoff into water.

Principles of sustainable forestry :- Every tree removed must be replaced. The forest must maintain its biodiversity, climate and mineral/water cycles. Local people must benefit from the forest. Selective cutting (taking only the largest, most valuable trees and leaving the ecosystem broadly unaffected) is encouraged.

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Humans and the Galapagos

Background

Where Darwin developed the natural selection theory. Isolation and small population sizes mean there is rapid evolutionary change. 50% of animals and 25% of plants are endangered. 

Habitat Disturbance

There are more humans, so higher demands for oil/water/sanitation. An oil spill in 2001 damaged marine and coastal ecosystems. Building and intensive agriculture have eradicated Scalesia trees, and caused destruction/fragmentation of habitats.

Resource over-exploitation

Whaling boats harvested whales/seals/sharks faster than they could be replenished. Turtles were taken and eaten by the crew. Sea cucumbers were over-harvested.

Introduction of species

Deliberate - cats hunt native species iguanas/lava lizards, fruit and veg outcompete native species, goats eat rock pursplane, outcompete giant tortoises.

Accidental - insects feed on plants and bring new diseases.

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