Topic 2: Biological Sucession

Question 1

BIOLOGICAL SUCCESSION

• The gradual change that occurs in the makeup of communities over time and space
• Species occupy a habitat because their specific needs are met
• As habitat changes, the composition of a community will also change over space and time
• Like organisms, communities tend to evolve from simple to complex
• Succession is like evolution of communities over long periods of time
• Organisms living in an environment cause change to the habitat and these provide new opportunities for other organisms to colonise the area.
• Organisms May change the environment by;
• Changing the soil structure and providing more organic matter
• Trapping the suns energy and making food for consumers
• Providing shelter for other organisms

Answer 1

PRIMARY SUCCESSION

• This is when organisms establish themselves in a new environment where resources are very limited. Examples include sand dunes and newly formed volcanic islands
• Not very common

Question 2

SECONDARY SUCCESSION

• This is when changes occur in a community, starting in an area where a community has been before, often due to damage by humans. Examples include fires, urbanisation & logging
• Very common

Answer 2

EARLY BIOLOGICAL SUCCESSION

• Communities must start with small autotrophs
• An early succession has only a small number of species present. They are fast reproducers, often called pioneer or coloniser organisms
• As communities become more established, their species diversity increases

Question 3

LATE BIOLOGICAL SUCCESSION

• There is a gradual movement from small, fast growing and reproducing organisms to larger, slow growing and slower reproducing organisms
• A stab,e or equilibrium community is developed

Answer 3

REPRODUCTIVE STRATEGIES

• In communities the individual species don’t all respond at the same rate
• Organisms have different reproductive methods to maximise the chance of reproduction and ensure success of the species
• Two main groups of organisms with different reproductive strategies and a continuum between them

Question 4

OPPORTUNISTIC (r) STRATEGIES

• Short life and produce many offsprings and have a high reproductive effort
• Generally found in new, harshly damaged or changing areas and they colonise quickly (early succession)
• They are very tolerant to low nutrient conditions. Examples including weeds
• GRAPH*

Answer 4

EQUILIBRIUM (K) STRATEGIES

• As succession occurs in the ecosystem, the environment changes so that the conditions are far more stable for those organisms that survive better in a stable environment (Late succession)
• Slow reproductive effort, long life, only produce small amount of offsprings
• Care for offsprings

Question 5

BALANCE

• K and r selected species are in equilibrium (both rely on each other)
• r selected species colonise areas of low resources very quickly but this is unstable
• K selected species cannot survive in low resource areas and therefore rely on r selected species to raise resources enough to allow them to colonise
• The rise in resources produced by K selected species allow r selected species to survive

Answer 5

• Most Species cannot be characterised as K or r
• Community shift over time is a gradual process which will contain many species that cannot simply be categorised as low or high reproductive effort. They just fit somewhere along the continuum