Week 23 Flashcards
What is the definition of these?
Evenness - Nestedness - Quantitative connectance - Vulnerability - Robustness -
Evenness – measure of equitability of inteactions in the community. – coffee plantations TRF example
Nestedness – e.g. specialist predator prey interactions within more general ones
Quantitative connectance – takes into account the weighting of feeding rates/fluxes in those interspecific connections rather than just regarding them as being equal.
Vulnerability – other side of coin to robustness
Robustness - how network responds to spp loss. Depending on which spp are taken out, e.g. in fragile networks – if take out one or two well connected spp., can have notable cascade effects through the community. How robust they are is what we need to know if we want to restore in the long-term. Can the community bounce back in face of adversity e.g. climate change?
Could you explain the ‘Constraints on predator design and behaviour’ again? Does it mean that if food chains were longer there wouldn’t be enough energy at the top for predators to survive on?
In addition to energy flow limitations and dynamic fragility
First, Energy Flow Hypothesis – max of 30% of E consumed at one trophic level is available as food at the next
Dynamic fragility – found that long food chains subject to severe fluctuations in pop size. So extinction of top predator is much more likely as food supply is unstable.
Constraints on predator design or behaviour – Would need a super-predator powerful enough to kill what we currently regard as top predators – none exist anymore like T-rex! Even some top predators are no longer e.g. Thylacine – marsupial top predator in Australia – ‘Tasmanian Tiger’, or top predators locally extinct e.g. wolves in UK but not on mainland Europe. Insect predators limited by anatomical/physiological limitations – oxygen supply to inner tissues.
However, they are subject to parasitism
Application - Quantitative pollination web – Trinia glauca Honewort
Example of food web approach to understanding community species interactions – food/resource acquisition is part of the interaction but so is pollination - also vital.
Trinia at the bottom where arrow points. Aliens include cotoneasters (spreading shrubs), Alexanders etc
Trinia is ant pollinated plant – very rare in UK
Pollination web colour coding - Black = native; green = alien spp.
In response to a question raised - to aid interpretation of the figure (foodweb/plant or pollinator interaction web)- the width of the bars at the bottom indicate abundances of specific plant species and the bars at the top indicate the abundances of particular pollinator species (the broader the bar, the greater the abundance). Lines linking plants to pollinators = interaction between these species. The more lines, the greater the number of interactions between a plant species and pollinators, e.g. one plant and many pollinators, one pollinator and many plant species or just many trophic level interactions. NB in some food webs, the extent of interaction may be represented by width of the lines connecting (more interaction = broader line width). OVERALL this fig indicates a great deal of interaction between plant and pollinator species what’s more, there’s much interaction between alien and native species. (plants and pollinators in both trophic levels)
Remember, restoration proposed = removal of alien plants = people climbing up or down on ropes and pulling out the alien species.
Alien species are deeply embedded in this plant pollinator network interactions. With these data, we can predict what would happen to Trinia if aliens were removed from this network.
With this information, were able to have a better-informed plan for removal, taking species out that would not lead to detriment of pollination of Trinia. For example Cotoneaster was found to be an important food plant for the ant pollinator of Trinia during Trinia’s flowering period so a staged removal was proposed to enable the effects of removal to be assessed.
What was McArthur & Wilson’s research?
plotted immigration and extinction rates for the range of replicate islands across a range of sizes – enables species richness to be explained – where lines representing rate plots cross – trace down to horizontal axis.
What is the island biogeography theory?
Distant small islands through to close large islands.
It’s referred to as the Equilibrium Theory of IBG as the number of resident species is the result of a balance between immigration and emigration/extinction rates. REMEMBER this is a dynamic equilibrium because immigration and extinction are continuous processes.
This theory is applicable to many types of islands and taxa and has a particular role to play in developing approaches in practical conservation biology.
Though the loss of habitat is greater because of the edge effect, does this mean the biodiversity is less?
Not necessarily – but will be different. May not be what is valued/desired. Ecotones – transitions – spp of two communities mix.
Couldn’t new species inhabit the ‘edge area’? Or help create ‘corridors’ between two habits and thus slow the rate of extinction?
Yes
Not really – need continuity in spp and conditions.
Are there any habitats that benefit (in terms of species diversity) by fragmentation?
Disturbance – early successional, annual spp.
Look at this schematic – where the coloured areas = habitat area.
The solid block on the left and the four squares on the right actually represent the same area of habitat. But on the right this is split into four fragments
We can study ecology at different levels of biological organisation. Which of the following presents levels of organisation in a logical sequence?
Individual, population, community, ecosystem
Which one of the following terms is used to describe a biological interaction in which an insect species pollinates a flowering plant?
Mutualism
Sea otters were hunted to extinction in intertidal communities along the Pacific coast of the USA. Their reintroduction led to a reduction in the sea urchin population and an increase in the kelp (seaweed) cover (upon which the urchins feed). This is an example of:
top-down control and trophic cascades.
If a community comprises 6 herbivores and 4 predators and there are 9 observed trophic interactions among these species, what is its connectance value?
0.375
6 times 4= potential interactions
9/24= 0.375
Which subject did the term “keystone” in relation to species originally come from?
Architecture
According to MacArthur and Wilson’s equilibrium theory of island biogeography, which islands should support the greatest diversity of species?
Large and near to a landmass
Which one of the following ecological principles was tested by Francis Gilbert using moss islands?
That fragmentation leads to habitat loss
