Genetics, populations, evolution and ecosystems

ecosystem

= natural unit of biotic components, together with the abiotic components through which energy flows and nutrients cycle

• can range from very small (e.g. rockpool) to very large (African grassland)

• simple e.g. desert, complex e.g. tropical rainforest

ecology

study of inter-relationships between organisms and their environment

abiotic factors

non-living

biotic factors

living

carrying capacity

certain size of population ecosystem can support

populations

group of individuals of one species that occupy same habitat at same time and are potentially able to interbreed

community

all populations of all different species living and interacting in a particular place at same time

habitat

place an organism normally lives, (characterised by the physical conditions and the other types of organisms present)

• e.g. stream: flowing water → aquatic animals, plants, water beetles

Microhabitat

Smaller units within each habitat within own microclimate

Niche

How organism fits into environment (where it lives, what it does, adaptations to biotic and abiotic factors)

i.e. role of organism in ecosystem

Competitive exclusion principle

• No 2 species occupy exactly the same niche

• when 2 species competing for limited resources, one that uses resources most effectively will eliminate the other

• e.g. 2 species of Paramecium

  • when both grown together with sufficient resources, pop density of both increases

  • as resources become limited, pop of P. aurelia increases and P. caudatum decreases, as P. aurelia outcompetes P. caudatum

Predator

Organism that feeds on another organism/ consumer(prey)

Not herbivore

growth curves

1. lag phase

   • no increase in pop size

   • adjusting to environment

   • synthesis of enzymes (gene expression regulation)

2. exponential growth phase

   • rapid pop growth (binary fission)

   • plenty of nutrients (space)

   • low levels of (toxic) waste

3. (transitional phase)

4. plateau/ stationary phase

   • birth rate = death rate

   • resources limiting pop growth

   • competition for nutrition

   • carrying capacity (k)

     • max pop size supported by resources in ecosystem

5. decline phase (if closed culture)

   • pop decrease, death > birth rate

     • resources depleted

     • build up of waste products

why use log scale

display large range of values e.g. exponential graph

e.g. bacterial growth (to show rate decreasing)

carrying capacity

= max stable pop size of species that ecosystem can support

• every individual within species pop has potential to reproduce and have offspring which contribute to pop growth

  • but abiotic and biotic factors prevent individuals reaching adulthood and reproducing

  • graph plateaus

abiotic factors affecting carrying capacity

e.g.

• light availability

• water supply

• temp

• amount of space available

• soil pH

• e.g. mammals: if temp of surrounding significantly lower/ higher than optimum body temp, will have to use significant energy to maintain optimum body temp (homeostasis)

  • = less energy for growth and reproduction

  • < individuals reach reproductive age and successfully reproduce

biotic factors affecting carrying capacity

interspecific competition

intraspecific competition

predation

interspecific competition

• between individuals of different species

• e.g. grey squirrels out-competed red squirrels in UK for habitat, nesting sites and food resources

  • grey had competitive advantage over other, so pop increased while red pop decreased

  • better adapted

• some cases, both pop sizes limited

  • both have access to fewer resources and so < chance to survive and reproduce

  • usually occurs if 2 species similarly well-adapted to habitat

intraspecific competition

• between individuals of same species

• availability of resources e.g. food, water, breading sites

• e.g.when resources are plentiful, pop of grey squirrels increase

  • as pop increase, there are > individuals competing for these resources e.g. food and shelter

  • at some point, resources become limiting and pop can no longer grow in size → carrying capacity reached

predation

• predator and prey species have evolved alongside each other so neither become extinct

  • = evolutionary arms race

• predator species adaptions e.g.

  • speed

  • night vision

  • eye sight

  • camouflage

• prey species adaptations e.g.

  • toxins/ poisonous

  • tough skin/ shells

  • group protection (of vulnerable)

• in stable community, number of predators and prey rise and fall in cycles, limiting pop sizes of BOTH predator ad prey

predator-prey cycles

1. no. of predators increase as > prey/ food available

2. no. of prey decrease as > predators so > are killed

3. no. of predators decrease as < prey available

4. no. of prey increase as < predators

• predator-prey cycle repeats

• fluctuations in pop size often < severe as food webs mean that predator may eat > 1 prey, so can eat another species

• disease and climatic factors may also cause periodic pop crashes

  • important as create strong selection pressures

succession

• ecosystems are dynamic = constantly changing

  • sometimes simple → complex

  • = succession

• during succession, biotic and abiotic conditions change over time

primary succession

occurs on bare rock/ any barren terrain

1. no organic soil present

2. pioneer species colonies bare rock

3. pioneers break up rock surface

   • organic material (soil) accumulates with broken rock as beginnings of soil

4. soil enables seeds of small, shallow rooted plants to establish

5. no. of niches and species richness increases

   • seeds from larger taller plants appear

   • compete with plants already present and community changes

6. trees dominate community

   • climax community dependent on environmental conditions

• species depend on those arriving by wind/ migration

secondary succession

1. bare soil

   • seeds

   • minerals water retention

2. grasses (1st species = rooted plants)

3. shrubs

4. trees

5. large trees

(no pioneer species)

primary and secondary succession

• biodiversity increases with time (more niches)

  • unless dominant species in climax community

• biomass increases

• climax community depends on abiotic factors

changes in environment during succession

• at each stage, certain species gradually change local environment so that becomes > suitable for other species (with diff adaptations) that haven’t colonised new land yet

• e.g. pioneer species make abiotic conditions < hostile for new colonising species

random sampling

no bias

systematic sampling

• chosen sampling points (possibility of bias)

• can be unrepresentative of whole area

distribution

how species spread throughout ecosystem

abundance

no. of individuals of that species

• can be measured by frequency

  • = likelihood of species occurring in quadrat

  • helpful for species difficult to count e.g. grass, but doesn’t give info on density and distribution

• % cover

  • faster but > subjective

  • plants in flower often overestimated while low-growing plants underestimated

frame quadrats

• quadrats laid randomly to avoid sampling bias

  • e.g. grid system, labelling each square with number and using random number generator

• can be used to measure

  • no. of individuals of one species

  • species richness

  • % cover

belt transects

• looking at how distribution/ abundance changes in physical conditions/ abiotic factors

• systematic sampling

• transect line represented by measuring tape, along which samples taken

• quadrats placed at regular intervals along tape and record abundance of each species within each quadrat

  • produces quantitative data

mark-release-recapture

• used for mobile organisms

• for single species in area

  • 1st large sample taken

    • as many individuals as possible caught, counted and marked

      • in way won’t affect their survival

    • returned to habitat and randomly mixes with rest of population

    • after sufficient period of time, another large sample captured

    • no. of unmarked and marked individuals within sample counted

    • proportion of marked to unmarked individuals, used to calculate estimate for population size

population estimate equation

N = (n1xn2)/m2

n1 = no. marked and released

n2 = no. in 2nd sample (marked + unmarked)

m2 = no. marked in 2nd sample

limitations and assumptions of m-r-r

• proportion of marked to unmarked same in 1st and 2nd samples

• have been no births/ deaths/ migrations over sampling period

• individuals redistribute themselves evenly after 1st catch

• marking doesn’t decrease individual’s chance of survival

  • due to increased visibility, decreased movement, toxicity etc.

  • mark rubbed off

• individuals all equally likely to be caught

  • not trap-happy / trap-shy