2.6 Ecology revision

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Ecosystems

• _{Ecosystem: the inter-relationship of living}

(biotic) and non-living (abiotic) elements in a specific area.

• _{Two major factors influence ecosystems:}

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Biotic and Abiotic Factors

• _{Biotic Factors - factors that make up the living} part of the environment e.g. competition,

predation, disease and availability

• _{Abiotic Factors – those that make up of the} non-living part of the environment e.g.

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Definitions

• _Population_{– a group of individuals of the same species that occupy the}

same habitat

• _Community_{– all the populations of different species that occupy the}

same area

• _Habitat_{– place where an organism lives}

• _Abundance_{– the number of individuals or one species living in a}

particular area

• _Distribution_{– where is a particular species is in a particular area}

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Abiotic Factors

• _Temperature

• _{Soil – moisture and pH} • _Light

• _{CO2 / O2 concentration} • _Rainfall

• _Humidity

• _{Topography – relief (height); slope angle; aspect}

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Biotic Factors

• _Disease • _Predation

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Analyzing data:

how to show there is a

correlation between two variables

• _{Plot a scatter graph of one variable on the} other

• _{Look for a correlation}

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Why might data be unreliable

• _{Other abiotic variables were not controlled} • _{Give named examples e.g. temperature}

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Field Ecology

• _{There are two main sampling techniques used to}

study communities:

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Random Sampling

• _{Form a grid using two tape}

measure at right angles

• _{Obtain random co-ordinates}

using random numbers generated by a calculator and place the quadrat at those coordinates.

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Different types of transect

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Analysing Data

• _{The means between sample can be tested to see whether}

or not they are significantly different using statistical tests such as the t-test.

• _{Data can also be analysed for correlations – there is a}

positive correlation if when one factor increases, the

other factor also increases. In negative correlations, if one factor increases, the other factor will decrease in value.

• _{Spearman’s rank correlation}_{is a statistical test that can}

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Productivity

• _{The productivity is the amount of energy available at}

a particular trophic level.

• _{The units for this are: per unit area in one year.}

• _The_{Primary Productivity}_{is the energy available in}

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GPP and NPP

• _{Gross Primary Productivity}_{is the rate at which}

plants convert light energy into chemical energy.

• _{However, energy is lost when the plant respires}

so there is less energy available to the primary consumer. This remaining energy is called the

Net Primary Productivity (NPP)

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Not all the light received by plants is

converted into GPP

• _{Some light is the wrong wavelength so can not} be absorbed by chlorophyll

• _{Some light reaches the leaf but passes}

through missing the chloroplasts containing chlorophyll

• _{Some light is reflected by the waxy cuticle}

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Net Primary Productivity

• _{Net primary productivity}_{is the rate at which} carbohydrate accumulates in the tissue of

plants or animals of In an ecosystem. It is measured in dry organic mass (kg ha-1_yr-1_).

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Energy Transfer

• _{The rate at which}

energy passes through each trophic level in a food chain is a

measure of productivity

• _{The sizes of the arrows} in the diagram

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Energy is lost at each trophic level

• _{Much of the energy is lost in respiration is lost} as heat or in movement.

• _{Energy is lost in indigestible parts of animals} and plants which can not be digested

• _{There is therefore less energy available to}

sustain living tissue at higher levels of the food chain, and so less living tissue can be kept

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Succession

• _{Succession is the term used to describe how species}

in a certain area change over time

• _{At each stage certain species can be identified which}

change the abiotic factors, especially the soil

structure, nitrate content and moisture so that it becomes more suitable for other species.

• _{These other species may then outcompete those}

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Features of Pioneer Species

• _{- the first organisms to colonise a barren area. Pioneer species}

have several features that suit them to colonisation:

• _{The production of a large amount of wind-dispersed seeds or}

spores so that they can easily reach isolated situations

• _{Rapid germination of seeds on arrival as they do not require a}

period of dormancy

• _{The ability to photosynthesize as light is normally available}

but other food is not – they are therefore not dependent on other animal species

• _{The ability to fix nitrogen from the atmosphere – even if there}

is soil, it has few nutrients

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Examples of Pioneer Species

• _{Barren rock}_{- blue-green bacteria, lichen.} • _{Barren sand}_{- Lyme grass,} _{Sea couch grass,}

Marram grass,

• _{Salt water}_{- green algae, Marine eel grass} Pickleweed, Cordgrass

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Succession

• _{Lichens and mosses are pioneer species} • _{Which are able to grow in no soil}

• _{They break down rock fragments so plants with}

short roots and able to grow in the soil

• _{Changes the soil structure enable other larger}

plants such as shrubs and trees to grow over time as the soil is able to retain more water.

• _{As plants die and are decomposed the organic}

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Climax Community

• _{- is the final stage in succession} • _{Has high biodiversity}

• _{This stable state comprises a balanced equilibrium of}

species e.g. deciduous woodland in the UK.

• _{In this state many animal and plant species flourish. This}

is called a climax community

• _{Within a climax community there is normally a}

dominant plant species and a dominant animal species.

• _{The community of species is stable if there is no change}

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Animals in succession

• _{The successional changes in animals are largely}

determined by the plant types that area available for food and as habitats.

• _{Dead lichens provide food for detritus-feeding mites.}

Mosses and grasses provide food for insects,

millipedes and worms. These are eaten by secondary consumers such as millipedes.

• _{The development of flowering plants and trees are}

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All successions have a number of common

features:

• _{The non-living environment becomes less hostile. –}

more soil, more nutrients, more plentiful plants to provide shelter

• _{A greater number and variety of habitats}

• _{Increased biodiversity – number of species reach a}

peak in mid-succession but due to dominant species out-competing pioneer and other species, some

species become eliminated from the community.

• _{More complex food webs}

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Secondary Succession

• _{Secondary succession occurs on land that at one time has}

already been colonized. This land may have been cleared during to human interference or a forest fire

• _{The land turns back to a climax community but this occurs more} rapidly than normal because spores and seeds are still alive and present in the soil which creates an influx of animals and plants through dispersal and migration from the surrounding area.

• _{This type of succession therefore does not begin with a pioneer} species but with organisms from subsequent successional

stages.