Species Guilds and Niches Flashcards
What is a guild?
Group of species, regardless of taxonomic position, that exploit the same class of environmental resources in the same way. They represent arenas of intense interspecific competition.
Give an example of a guild
Seed-feeding desert rodents:
- Comparison between hotter Sonoran Desert and cooler Great Basin Desert
- Essentially the same, they are geographically repeatable
- Size structured guild
What are the components of plant niches?
Plants require the same fundamental resources: light, CO2, nitrogen, phosphorous, potassium, micronutrients and water.
- Habitat - physical and chemical components of environment
- Life-form component - plant’s size and annual productivity
- Phenological component - seasonal pattern of development
- Regeneration component - germination and seedling establishment
What is Tilman’s Model?
Zero Net Growth Isoclines (ZNGIs)
Argued that plant species may coexist when competing for the same limited resource through their different utilisation of this resource.
Resource ratio hypothesis states that there are more ratios of resources than actual resources.
Graphical theory of consumer-resource interactions.
Explain the resource-ratio hypothesis
Two plant species may co-exist at equilibrium despite requiring the same resources in limited supply, provided that:
- One species is limited by one resource and the other species is limited by another.
- Each species consumes more of the resource that limits its growth.
Through utilisation of different resource-ratios, multi-species coexistence is theoretically possible.
What factors can prevent a community reaching equilibrium?
Gradual Change
Disturbance
Random fluctuation in space and time
Give an example where niches are NOT necessary
Drosophila guilds exist despite identical niches.
Share the same resource but are patchily distributed and are ephemeral
Low interspecific competition
Aggregated spatial patterns
Egg laying distribution over rotting fruit leaves areas free of other species.
Probability refuges - Some units of resource will have little or no competition which can serve as refuges for weakly competing species.
Explain the lottery hypothesis
In fish guilds of the Great Barrier Reef, space not food is limiting resource.
Reef fish have home ranges and require a particular bit of space to succeed.
As space becomes randomly available, fish larvae recruit into gaps like a lottery - randomly selected.
Unpredictable environment prevents generalist species from dominating.
Gap colonisation on first come first served basis.
What was Hubbell’s theory of non-equilibrium in plant communities?
In tropical forest tree communities, more species exist than niches available.
Do not co-exist in the long-run, random path of immigration and extinction due to community disturbance.
Island forests should be dominated by one species - differing between islands.
For large communities, rate of extinction is slower than speciation.
Equilibrium or non-equilibrium?
Not mutually exclusive
Communities exist somewhere along a spectrum
May be at equilibrium at some scales and not at other scales.
