Community and succession

Succession

the change in structure and species composition of a community over time

Climax community (2)

a stable, self-perpetuating community that has reached equilibrium with its environment, and no further change occurs

Primary succession

the change in structure and species composition of a community over time in an area that has not previously been colonised

sere

the sequence of communities with the different species and structures

xerosere

a sere in a very dry environment

seral stages (2)

stages of a sere, each stage changes the environment and makes it more suitable for other species

pioneer species

the first species to colonise a new area in an ecological succession, e.g. algae, lichens and mosses in a xerosere

Explain stage 1 of the formation of a climax community on a bare rock (3)

spores of pioneer species are deposited on bare rock by wind or animals, algae and lichens colonise bare rock, lichen produces enzymes that erode rock forming a thin layer of soil

What kind of relationship do the algae and lichens have?

a mutualistic relationship

Explain stage 2 of the formation of a climax community on a bare rock (3)

weathering by erosion by lichens and accumulation of dead and decomposing organic material leads to the formation of a primitive soil, this allows animals to survive when there is enough food for them, like mites and ants and spiders

Explain stage 3 of the formation of a climax community on a bare rock (4)

wind blow spores allow mosses to grow, as soil develops grasses and small herbaceous plants outcompete mosses and become established, favouring well-dispersed species that make a lot of seed that can germinate in direct sunlight, animals present at this stage are nematodes, ants, spiders and mites

Explain stage 4 of the formation of a climax community on a bare rock (2)

shade-tolerant species become established due to tall grasses, so community becomes more complex

Explain stage 5 of the formation of a climax community on a bare rock (4)

soil becomes thicker as these plants and animals decay, soil becomes more mineral rich, water held more efficiently with greater quantity of humus, deeper-rooted plants, shrubs and small trees outcompete herbaceous plants as soil builds up

Explain stage 6 of the formation of a climax community on a bare rock (2)

soil continues to deepen and increase in minerals and in humus, over a long time large trees outcompete shrubs and small trees to become established growing to form a climax community

WHat are 2 examples of large trees that outcompete shrubs and small trees in the formation of a climax community?

oak and beech

What are 3 features of a climax community? (3)

great species diversity, complex food web, dominated by long-lived plants

What is important to note about the species in a climax community?

species of climax community depends largely on climate so its known as a climatic climax community

Why does plant diversity decrease slightly from pre-climax state?

tree canopy limits light intensity reaching woodland floor

As a xerosere progresses, where are increases seen? (5)

soil thickness and availability of water humus and minerals, biomass, biodiversity, resistance to invasion by new species, stability to disruption by environmental challenges

Secondary succession (4)

the changes in a community following the disturbance or damage to a colonised habitat, the area rapidly becomes re-colonised by a succession of organisms, species depend on conditions prior to disturbance, seeds spores and organs of vegetative reproduction may remain in soil

What assists colonisation of the habitat in secondary succession?

dispersal of plants and migration of animals

Commensalism (3)

Interaction between two species where one benefits, and the other is unaffected, like a squirrel on an oak tree

Why does secondary succession have the same stages as primary succession but secondary succession is faster?

soil is fertile and organisms are present in secondary succession

What are some examples of rapid colonisers? (5)

grasses, herbaceous plants, heathers, brambles, birch trees

Disclimax

Where human interference can affect a succession and may prevent the development of the climatic climax community

How is grazing by sheep and cattle an example of disclimax?

maintains grassland and prevents the shrubs and trees of a normal succession from growing

How is farming of land an example of disclimax?

removes all except deliberately introduced species and great effort is expended in excluding all others

How is deforestation an example of disclimax?

removes a community of large trees and smaller trees may be replanted

How is migration a factor affecting succession? (2)

arrival of spores, seeds and animals is vital for succession to progress, immigrating non-native species may spread themselves widely altering community and soil

How is competition a factor affecting succession? (2)

plants compete for resources like light, space, water and nutrients, animals compete for food, shelter, space and reproductive partners

Intraspecific competition

competition between individuals of the same species

Interspecific competition

competition between individuals of different species

Niche (2)

the role and position a species has in its environment, including all interactions with the biotic and abiotic factors of its environment

Why can’t two species occupy the same niche in a specific habitat?

only the one with the competitive advantage will survive

What is the competitive exclusion principle? (3)

when two species occur in the same habitat, one will outcompete the other, as two species cannot occupy the same niche

Symbiosis

the association between individuals of two species

What is the range of interdependence in facilitation?

long-term or loose association

How does facilitation help in an ecological community?

it provides better resource availability and refuge from physical stress, predation and competition

Mutualism (2)

an interaction between organisms of two species from which both derive benefit, like the relationship between flowering plants and pollinators