Lecture 9 - (Freshwater Ecology) - Stream Communities: Biotic and Abiotic interactions

What are main filters that affect community composition? that are scales of scales of influence

• watershed / basin filters

• valley / reach filters

• channel unit filters

• Microhabitat filters

What are mesohabitats of a river?

areas that are distinctive on the river bottom, still affected by differences in distribution because of biotic and abiotic factors

How does competition as a biotic factor affect species distribution?

• occurs when individuals compete for resources which are in limited supply

• very strong competition can lead to extinction in that area of a species

What is interspecific competition?

competition over limited resources between individuals of the same species

What is intraspecific competition

competition for limited resources within individuals of the same species

describe exploitation as a form of competition

where food or space is limited

What is interference as a form of competition?

aggressive interactions between competitor species / individuals - e.g species having limited algae to eat on a rock

• resource partitioning can reduce competition

Give an example of a species showing evidence of competition

Baetis - a fugitive species - good coloniser but poor competitor

McAuliffee (1984) - reduced Glossoma (type of caddisfly) and saw the abundance of baetis increase = suggests competition between species

Give an example of a species using resource partitioning to reduce competition

Mississippi Stream - types of fish were separated out over a river, with only two types failing to separate

What species count as predators in freshwater

fish

invertebrates like stoneflies / dragonflies etc

what are prey tactics to reduce the risk of predation

• reducing encounter rates - e.g low movement rates / reduced visability

  • reducing attack and capture rates - e/g armor / playing dead (thanatosis)

Give an example of a prey who has adapted to avoid predation

Water fleas in lakes

• Thanotosis - playing dead

• Morphological - e.g daphnia tail / helmet spines

Explain how the physical environment may limit opportunities for biotic interactions

‘the harsh benign’ - Peckarsky (1980)

• a gradient from harsh to benign

• Harsh = few competition / predation effects

• Benign = environment allows for well developed competition / predation effects

How do harsh environments impact communities?

harsh environments experience disturbance e.g waves on rocky shores

• disturbance = any discrete event in time that removes organisms and opens up space to be colonised by individuals of the same or different species e.g fires in woodlands

Describe the intermediate disturbance hypothesis (IDH)

a graph showing the relationship between disturbance and species diversity

• at high levels of disturbance, only specialised, small numbers of animals can live there

What is the patch dynamics concept?

the idea that disturbance is continually opening up patches for colonisation and succession - fugitive species have recurrent opportunities for recolonisation

define fugitive species

species that is adapted to rapidly colonise new environments - normally found in unstable environments. De

Define competitive dominants

the degree to which a species is making up the biomass of an environment or have influence over other species in an area

what are reciprocal subsidies?

energy, organisms and nutrients that move between ecosystems

how are salmon life cycles linked to reciprocal subsidaries

• salmon lay their eggs in freshwater before dying = their carcasses bring nutrients into freshwater and riparian vegetation

• their carcasses input carbon, nitrogen and phosphorous into the system

  • their carcasses provide food - e.g for caddisflies

what is an example showing how aquatic invertebrates get eaten by terrestrial invertebrates

stoneflies can get eaten by terrestrial spiders

• e.g aquatic species averaged 50% of the diet of dominant spiders