Lecture 7 (Freshwater Ecology) - River Ecology: Adaptations, movement and colonisation

How do oceanic organisms colonise the land and freshwater systems?

through estuaries and the coast

How does secondary colonsiation work?

Land ancestors - e.g pulmonate snails - who came from the land and adapted over time

How has New Zealand’s insects evolved differently?

New Zealand over time broke off from the mainland, so evolved in isolation, but shares many characteristics with british insects. = called covergent adaptation

What are adaptations to flowing water?

• Air breathing

• Plastron -(air bubbles) e.g insects - a series of hair or bumps used to trap air against the body

  • tracheal gills

What are adaptations to coping with and exploiting flow?

• Streamlined body - ‘hydrofoils’

• Suckers

• Hooks

• Modified feeding appendages

  • silk

How has the plant water crowfoot adapted to freshwater systems?

• Has streamlined leaves

• Reduced resistance to flow, through streamlined leaves so the flowers don’t breal

  • Submergent macrophyte - flowers occassionally stick out over summerHo

How has the plant brandy bottle adapted to life in freshwater?

• has two different leaf types:

• 1 - on the surface for photosynthesis

  • 2 - submerged leaves which bend with the flow = slowing the flow which encourages accumulation of sediment

Give examples of invertebrates which are adapted to freshwater through streamlining?

• nymths - are long which allow easier movement through the water

  • Caddisfly larvae - have streamlined cases which provides camoflage and protection from fish

Give examples of insects who are adapted to freshwater through suckers?

• Blackfly larvae - filter water with a headfan - abdominal hooks are used to anchor the larvae to the substrate in fast flowing water

• Mayfly larva - have modified gills that create suction = must be in fast flowing water to get enough oxygen 

How is silk used to adapt to life in freshwater?

Caddis - different to other caddisflies, as they don’t build cases. They build silk nests for attachment / shelter and feeding. 

What insect provides evidence that some insects move upstream

Gammaridae - evidence they move upstream, also at night, and at certain times of the year

What insects fly upstream to lay eggs?

mayflies - adults swarm, mate and females fly upstream to lay eggs

What are osmoconformers

organisms that allow their internal osmolarity to change with the surrounding environment - found in environments with stable salinity levelD

define osmoregulators

organisms that actively regulate their internal osmorality to remain constant - regardless of external environment

• Have specialised structures like gills to remove excess water / ions

  • Found in areas with fluctuating salinity levels e.g freshwater

what is osmolality?

the concentration of osmotically active particles in a solution - measured per kg of solvent

how is the aquatic plant water crowfoot adapted?

• streamlined leaves = reduced resistance to flow so leaves dont break

• Submergent macrophyte = flowers occassionally stick out over the summer

• winter - tiny sprigs left (rhizomes) - as plant sheds biomass for winter

• Spring - rhizomes grow as weather improves

What is macroinvertebrate drift?

the movement downstream of invertebrates volantarily or involantarily

What are the three types of macroinvertebrate drift

A - Catastrophic = due to unfavourable conditions

B - Behavioural = patterns of behaviour

C - Constant = occurring all the time at low levels

When is behavioural drift at its peak?

peak at maximum darkness to avoid predation by fish

• done by invertebrates like mayfly baetis

  • varies with season, daily and insect life stage

What are the advantages of macroinvertebrate drift?

• when food is scarce

• avoid unfavourable conditions - e.g pollutants / temperatures / floods etc. 

• to avoid predation

What is the lateral dimension of stream and river ecosystems

riperian zone floodplain to the stream channel

What is the longitudinal dimension of stream and river ecosystems

upstream to downstream

What is the vertical dimension of stream and river ecosystems

stream channel to hyporeos groundwater

what is the temporal scale of stream and river ecosystems?

the range of time, from seconds to millennia 

What is the hyporheic zone?

the region of sediment and porous space alongside a streambed, where there is mixing of ground water and stream water

• can be over 100cm deep

• can be over 2km wide from stream channel

What are creatures who live in the hyporheic zone called?

hyporeos

What are permanent hyporheos?

they always live there

• includes copepodes, rotifers etc.W

what are occasional hyporheos?

Only spend part of their lives in this zone

• do not have the same adaptations as permanet hyporheos e.g caseless caddis

What are the conditions of the hyporheic zone?

• temperature - less variation than the surface

• light - does not penetrate >4-5x grain size of sediment

• Nitrate - hyporheic zone plays role in transfer between terrestrial and aquatic environments

  • dissolved oxygen - declines with increasing depth - e.g at 30cm - can be 5% of what is at the surface

What are the advantages to living in the hyporheic zone?

• lack of predators

• plentiful food e.g biofillm, bacteria

  • survival during adverse conditions e.g storms

What are disadvantages to living in the hyporheic zone

• reduced current velocities

• low dissolved oxygen, high CO2

• Accumulation of waste