By Edward Harrison. This refers to the amount of energy fixed per unit area per unit time in an ecosystem by a particular trophic level. The net productivity.

OPTION G: ECOLOGY AND CONSERVATION

by Edward Harrison

PRODUCTIVITY

This refers to the amount of energy fixed per unit area per unit time in an ecosystem by a particular trophic level. The net productivity is affected by the amount of energy used in respiration.

Net productivity = gross productivity – energy used in respiration.

NICHE

Each organisms fulfils a unique role in its ecosystem, called its niche.

The abiotic and biotic resources interacted with by the organism form parts of its niche.

If the factors within the environment falls outside what an organism can tolerate, it will not be found there.

THE COMPETITIVE EXCLUSION PRINCIPLE Two species cannot coexist in the same

habitat if their niches overlap. Eg. Grey squirrels and red squirrels.

One species will either decline and become extinct, or both species will narrow their niche. Ie. Red squirrels have become extinct throughout most of Britain.

This is called the competitive exclusion principle.

SUCCESSION

In an ecosystem, abiotic factors limit the biotic factors, in other words, abiotic factors limit the growth of plants in an ecosystem. However biotic factors can effect the abiotic factors, changing them so that the environment is better suited to other species. This is known as succession.

PRIMARY SUCCESSION

This is the same as succession, except it begins in a location where initially no other species are located, with pioneer species arriving in the environment and starting the development of an ecosystem which will eventually stabilise.

INVASIVE SPECIES

Human activity can lead to the introduction of one species into an area where it did not occur naturally. Because of the niche overlap with native species and the lack of predators and other limitations as in its natural habitat, the species can become so reproductively successful it threatens the diversity of the habitat, and becomes invasive.

BIOLOGICAL CONTROL

This is the introduction of an invasive species’ natural predator to a habitat to control the spread of the invasive species.

BIOMAGNIFICATION

Certain toxins can build up in the body of an organism, especially if they are fat soluble. This is called bioaccumulation.

The effects of this toxin can be magnified further up the food chain, with top predators having increased concentrations of the toxin in their body. This is called biomagnification.

INDICATOR SPECIES

An indicator species is an organism which is only present when certain conditions in the environment are met.

The presence of absence of indicator species is a good indicator of the environmental conditions.

BIOTIC INDEX

A biotic index compares the relative frequency of indicator species.

The number of individuals of each indicator species is determined, and then each number multiplied by a pollution tolerance factor, and a weight average determined.

HABITAT LOSS

Habitat loss is a significant variable in the extinction of species. Habitat fragmentation by human activity can cause small populations to become isolated. Because of their small size these populations can become extinct.

Activities such as mining and agriculture can cause habitat fragmentation. When designing nature reserves it is important to create corridors between patches to maintain the connections between isolated populations.

THE R-K SPECTRUM

In a predictable environment it better to invest in long-term development (K-strategy).

In an unstable environment it is better to invest in producing as many offspring as quickly as possible (r-strategy).

K-STRATEGIES

A K-strategy involves investing more resources in development and long-term survival. This involves a longer life-span and later maturity, reproducing more than once, larger body size, parental care, and fewer offspring.

The “K” refers to the variable normally used to represent carrying capacity.

R-STRATEGIES

An r-strategy involves investing more resources into the production of many offspring, with a short lifespan, early maturity, reproducing only once and having a small body size.

Disruption to ecosystems favours r-strategists such as pest species.

FISHING

Fish are an important food resource. An important component of managing

fish is clear data about fish populations. The concept of maximum sustainable

yield is related to the sigmoid growth curve.

MULTIPLE CHOICE QUESTION 1

Which of the following is not a K-strategist?

A. An elephantB. A parrotC. A rabbitD. A wolf

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MULTIPLE CHOICE QUESTION 2

In the equation for the Simpson Diversity Index the “N” represents what?

D=N(N-1) ∑n(n-1)

A. Number of individuals of a particular species

B. Total number of all organisms foundC. Number of native speciesD. Number of alien species

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MULTIPLE CHOICE QUESTION 3

Which point on the graph is the exponential growth phase?

A B

C

D

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MULTIPLE CHOICE QUESTION 4

Which if the following describes a tundra biome?

A. Wet, saturated soil conditions, with wide biological diversity.

B. Large temperature range between seasons.

C. Warm, with a moisture deficit.D. Tree growth hindered by low temperat

ures and short growing seasons.

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MULTIPLE CHOICE QUESTION 5

The first species to appear on a newly formed island is known as the...

A. Native speciesB. Alien speciesC. Pioneer speciesD. Invasive species

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