Edexcel A level Biology B Student Book 2 ActiveBook
This document contains summarised notes for Topic 10 Ecosystems, taken using the Pearson Edexcel B biology activate textbook. Notes taken with referencing to specification.
WHAT IS ECOLOGY
ECOSYSTEM – is an environment including all the living organisms interacting within it,
the cycling of nutrients and the physical and chemical environment in which the
organisms are living. They can range in size.
HABITAT – place where organism lives. Small habitats are microhabitats
POPULATION – a group of organisms of the same species, living and breeding together
in a habitat
COMMUNITY – all the populations of all the different species of organisms living in a
habitat at any one time.
NICHE – the role of the organism in the community. Several organisms can share the
same habitat, occupying different niches.
ABIOTIC FACTORS – non-living elements of the habitat of an organism. (temp, light, pH,
rainfall)
BIOTIC FACTORS – living elements of a habitat that affect the ability of a group of
organisms to survive there.
BIOSPHERE – all of the areas on the surface of the Earth where living organisms
survive.
~ It’s too large, so it can be divided into smaller parts.
~ These are called BIOMES – generally subdivided into smaller ecosystems.
SUCCESSION – the process by which the communities of organisms colonising an area
change over time are replaced by other, more varied communities.
PRIMARY SUCCESSION – can be seen after a volcanic eruption or landslide.
~ Starts with empty inorganic surface such as bare rock
1. Natural event occurs
2. Pioneer species (algae, fungi)
3. Soil forms (rocks break into small grains)
4. Root system established when they die and nutrients are given to the soil
5. Plants form, as plant biodiversity increases, animal biodiversity increases.
6. A CLIMAX COMMUNITY is reached, where the biodiversity and range of species are
generally constant
CLIMATIC CLIMAX COMMUNITY – it
has many species and is stable if there’s no change to the environment.
PLAGIOCLIMAX – are constant and self-sustaining but aren’t natural. They are the result
of human intervention
SECONDARY SUCCESSION – the development of an ecosystem from existing soil that
is clear of vegetation. Occurs as rivers shift their courses, after fires and floods,
disturbances caused by humans.
1. Pre-formed soil which already contains seeds, microorganisms and roots.
2. Forms a different climax community than primary which depends on abiotic factors:
rainfall, temp, soil fertility, type of colonisation
THE EFFECT OF ABIOTIC FACTORS IN POPULATIONS
LIGHT – CLIMATIC – main source of all energy
PLANTS - direct effect on the numbers of organisms
~ Plants are dependent on light for photosynthesis
~ Some plants reproduce early to avoid the shade caused by larger plants
, ~ Other plants are able to photosynthesise and reproduce successfully in low light
levels, often by having extra chlorophyll or different ratio of pigments
ANIMALS - indirect effect as a result of the distribution of food plants
~ Seasonal light changes affect reproductive patterns in many animals
TEMP – CLIMATIC – helps grow and successfully reproduce organisms
~ Reproduction doesn’t occur above or below that range
~ The extremes of temp determine where an organism can live, not the average
~ The temp of the environment affects the rate of enzyme-controlled reactions in
plants and ectothermic animals.
WIND – direct effect on organisms
~ Wind increases water loss from the body and cooling and so adds to the
environmental stress on an organism.
~ Fewer species can survive in areas with strong prevailing winds.
WATER CURRENTS – organisms have to flow with the current, be strong swimmers or
be able to attach to the surface and resist the force of the water.
WATER AVAILIBILITY - TOPOGRAPHY
~ Affected by factors such as precipitation, rate of evaporation, and edaphic factors
(rate of loss by drainage through the soil)
~ Limited supply – severe problems
~ If water stress is too severe organisms will die unless some have special
adaptations to enable them to survive in very dry conditions.
~ An increase in the availability of water can lead to a huge change in habitat and to
a massive increase in population size of some organisms.
EDAPHIC FACTORS - relates to structure of the soil and affect the populations
associated with it
~ Sand has a loose, shifting structure that allows very little to grow on it.
~ Plant populations that are linked by a massive root can and do survive on sand.
They reproduce successfully and bind the sand together, which makes it more
suited for colonisation by other species.
Soils that contain a high proportion of sand are light, easily worked and easily warmed
but they are easily drained.
THE EFFECT OF BIOTIC FACTORS ON POPULATIONS
COMPETITION
COMPETITIVE EXCLUSION – when the fastest growing competitor eliminates a slower
growing competitor and completely takes over an area.
Plants compete for: Animals compete for:
~ Space ~ Food
~ Light ~ Territory/shelter
~ Nutrients ~ Mate/s
PREDATION (CYCLICAL RELATIONSHIPS)
~ Predator-prey relationships cause the population to oscillate in a repeating cycle.
~ As prey population increases there’s more food for the predators and so, after an
interval, the predator population grows too.
~ The predators will increase to the point where they are eating more prey than are
replaced by reproduction, so numbers of prey falls. This reduces food supply of the
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