Community Ecology Flashcards
What is a food web?
A representation of feeding relationships in a community that includes all the links revealed by dietary analysis
How many trophic levels do communities generally have?
2 to 5
What is the energy flow hypothesis as to why there is a general maximum of 5 trophic levels?
A maximum of 30% of energy consumed at one trophic level is available as food to the next
What is dynamic fragility with relation to a low maximum number of trophic levels?
In model communities, webs with long food chains are prone to more severe population fluctuations. Extinction of the top predator was more likely in long chains
What is the equation for connectance in a good web?
Actual number of interactions / possible number of interactions
What is a keystone species?
A plant or animal that plays a unique and crucial role in the way an ecosystem functions
What are food webs crucial to in ecology?
Alien species - seeing where they get to Organic farming - better pest control Pollination - how to conserve it Landscape level conservation Restoration - has it worked
What is restoration?
Returning a system to a close approximation of it’s condition prior to disturbance, with both the structure and function of the system recreated
What is restoration ecology?
The study of how to repair anthropogenic damage to the integrity of ecological systems
How is restoration ecology a community level phenomena?
Requires restoration of key linkages
Removal of introduced species is part of this
Biocontrol can be part of solution
What is biocontrol?
The use of living organisms, such as insects or pathogens, to control pest populations
What is rewilding?
Large-scale conservation aimed at restoring and protecting natural processes and core wilderness areas, including reintroducing apex predators and keystone species
What are the living dead?
When the last few remaining individuals of a species don’t form a viable population
What are the 3 challenges with restoration ecology?
- The fuzzy target problem
- The moving target problem
- The experimental design problem
What is the fuzzy target problem?
Communities vs populations
If we don’t know exactly how the community should be, how will we know if it is ever restored
Similar reference sites must be used
What is the moving target problem?
Communities are dynamic, not static, and change in the absence of disturbance - may no longer be right to restore it to original state
What is the experimental design problem?
There is a lack of scientific control and replication
What would be a control?
Is habitat restoration an art or a science?
The Field of Dreams hypothesis
Brown (1994) ‘The artistry of restorations will give way to an applied science’
What is the field of dreams hypothesis?
You can reestablish a natural ecosystem by replanting trees and other methods, from which the natural system will reestablish itself and organisms will naturally recolonise
‘If you build it, they will come’
What are some last problems with restoration ecology?
Little development of general theory
Not much transfer of methodologies
Persistence of the restored system - how long does restoration last?
Resilience of the restored system
What are ecosystem services?
Goods and services provided for free by the environment (includes ecosystem tourism)
Why use a community approach to ecosystem services?
Networks show the links between a species in a community
Traditional approach in ecology - species list, abundance, indicator species
Interactions form the basis of sustainable agriculture (e.g. pest control and pollination)
Interactions can have a profound impact on a community’s response to species loss, stress and ecological restoration
Why is pollination so important for strawberries?
If they are not pollinated evenly on seeds all around the fruit, they grow uneven and are worth less
How is pest control of agriculture monitored?
Previously by indicator species, but new evidence shows they do not provide the data needed
Need to understand how species interact
What is an example of restoration of water filtration?
Delaware watershed (2000 square miles) brought filtered water to New York City. Water was being polluted, and the choice was to build a 6-8 billion dollar filtration plant or restore and protect the natural filter
Features of watershed
Highly efficient and valuable Crop filled valleys Forested mountains Streams feeding 19 reservoirs 1.8 billion gallons a day No need for filtration paint
How do natural filters work?
Soil, roots and microorganisms break down contaminants (fertilisers, N2 from car exhausts)
Aquatic plants absorb up to 50% of nutrients
Wetlands continue to filter and trap sediments and heavy metals
Reservoirs - sediment sinks to bottom
Small doses of chlorine and fluorine are all that’s needed
What are some methods used in habitat restoration?
Linking up fragments of habitat Natural regeneration Planting trees between fragments Felling non-natives Reintroducing large mammals
What percentage of introduced species establish?
10%
What percentage of established introduced species become weeds/pests?
10%
How to study invasions?
Describe them
Model them
Manipulate them
What is the issue with the Guam brown tree snake?
Invasive species
Nest predator, has driven 10 endemic bird species to the point of extinction
How to establish a biocontrol agent
Introduce it in small amounts - better than all at once
What is the problem with the Himalayan Balsam in the U.K.?
One of the top 20 invasive species in the UK
Grows well in wetland communities
Explosive seed pods
Produces 10x more nectar than any UK species
Introduced in 1839
Competes with native plants for pollinators - has more nectar so attracts more insects
How was the pollination of Himalayan Balsams studied?
Experimental plot - removed balsam flower heads every week - allows balsam to still compete directly with native plants but not for pollinators
What was the result of the Himalayan balsam study?
On average more visits from pollinators if balsam is present (opposite to expectation)
However, 80% of pollen on insects was balsam pollen
Islands in ecology
High conservation status
Evolutionary hot houses
Badly damage by crops, tourism and alien species
Huge scope for restoration
What areas does ‘islands’ include?
Lakes (islands in a sea of land) Mountain tops (high altitude islands in a low altitude island) Habitat fragmentation (islands of habitats)
What is the theory of island biogeography?
A theory aimed at predicting the number of species that would exist on a newly created island and able to explain the species richness of islands
What is the natural history of islands?
Islands contain fewer species than comparable pieces of mainland
Big islands > species than small islands
Small islands > species than distant islands
Species-area relationship
Reasons for island natural history
- Habitat diversity: more habitats on continents/large islands than small islands
- Equilibrium theory (McArthur & Wilson, 1967): the number of species on an island is determined by a balance between immigration and emigration/extinction - more immigration onto closer islands
What major habitats are undergoing serious fragmentation?
Ancient broadleaf woodland Heathlands Caledonian pine forest Tropical dry rainforest Tropical rain forest
What are the two main changes due to habitat fragmentation?
- Reduced area
- Edge effect - more light, wind and water affected edges of habitat, which can cause the habitat area to decrease further
What groups are prone to extinction following fragmentation?
Predators Large species (need large areas to feed) Habitat specialists (fragmentation affects germination time, temp, etc)
Reducing the impact of fragmentation
Wildlife corridors (connect habitats to each other) However, they are expensive and there is a lack of research on them until recently
What are the benefits of wildlife corridors?
- They will slow rate of extinction
2. Predators most affected by fragmentation so corridors benefit predators most
Wildlife corridors were studied using mesocosms. What is a mesocosm?
An outdoor experimental system that examines the natural environment under controlled conditions
In a study of species in habitats of 1, 10 and 100 Hectares, what there the species loss results?
Smallest plots = fastest species loss
Even 100 hectares lost 50% of species in 10 years
What impact does climate change have on most organisms?
Increase in mean global temperature is associated with an average advancement in phenology of life history events e.g. flowers man bloom earlier in the year
How much earlier is the average first flowering date of British plant species?
4.5 days earlier since 50 years ago
How does in increased temperature affect harlequin frogs?
Increased temperature makes pathogens more virulent. 67% of the 110 harlequin frogs are now extinct - temperature now optimum for outbreaks of frog fungus
