Factors Influencing Species Distributions: Dispersal And Habitat Selection Flashcards
Whats the first factor limiting distribution
Species can survive outside of its current range but is absent because:
- Cannot get there (dispersal)
- Does not recognise it as a suitable habitat (habitat selection)
What is the 2nd factor that may be limiting a species distribution
Species could not complete its life cycle outside of its range because of:
- Interactions w/ other species (predation, disease, competition, mutalism, symbiosis)
- Impacts of physical and chemical factors (temperature, light, moisture)
What is the 2nd factor that may be limiting a species distribution
Species could not complete its life cycle outside of its range because of:
- Interactions w/ other species (predation, disease, competition, mutalism, symbiosis)
- Impacts of physical and chemical factors (temperature, light, moisture)
When is dispersal gradual
Dispersal by diffusion: Sea Otter Enhydra lutris.
Gradual recolonization of suitable habitat after population crash from hunting
When is dispersal rapid
When individuals move across large distances often crossing unsuitable habitats and establish a population in a new area.
Known as jump dispersal
What are some successful biological control agents
Are host specific
Life cycles are synchronous with the pest
Have high intrinsic rates of increase
Are able to survive when few prey are available
Have great searching abilities.
What is habitat quality in terms of habitat selection as a limiting factor of distribution
Some habitats promote better rates of growth/survival/reproduction than others.
Habitat features provide clues to an organism about what is available (food, predators, shelter)
Many species have evolved mechanisms for detecting the habitats where they are likely to ‘do best’
Habitat quality is a function of:
Habitat features (food supply, shelter. predators)
Density of conspecifics (overcrowded habitat less desirable)
Habitat quality is not constant changes with density
What happens high quality habitats
Often occupied first and the species may be absent from areas they could survive.
When highest quality habitat become ‘full’ its individuals will colonize other areas.
What happens high quality habitats
Often occupied first and the species may be absent from areas they could survive.
When highest quality habitat become ‘full’ its individuals will colonize other areas.
What is ideal free distribution (Fretwell, 1972)
When all individuals are free to move into any habitat without constraints
- Highest quality habitats occupied first
- When density reaches a point the in the higher quality habitat A, B habitat becomes more suitable than A and individuals start to colonize B.
- When density of B gets high, habitat C is occupied.
- When high density in all habitats, densities will vary but suitability is equal due to intra-specific competition for resources.
What is ideal despotic distribution (Fretwell, 1972)
When all individuals are not free to move between habitats and the highest quality habitat is protected by territorial behavior.
- Subordinate individuals can be pushed into lower quality habitats
- Density of poorer habitat may be equal or higher to that in high quality habitat
- Fitness will be lower in poor habitat
Give example of the Ideal Free Distribution theory.
Herring gull, Newfoundland, Canada.
Three types of potential nesting sites exposed rocky terraces, grassy meadows, turf covered slopes occupied by puffins.
Rocky habitat occupied first density was higher than other two habitats.
Eggs & chicks were heavier in rocky habitat, no. of chicks fledged per adult still same. No difference in breeding success due to higher density in rocky habitats.
Give an example of the Ideal Despotic Distribution.
Yellow legged gulls, Medes Island, Spain.
Shrubby areas protected from predators & shade
Grassy meadows more exposed.
Nests built and eggs laid in shrubby habitats first
Territorial species - high quality habitat protected so density in high quality habitat didn’t exceed that in the lower quality habitat.
Give an example of climate change impacting species distribution by altering habitat selection behaviors.
Cod in Skageraak.
Cod normally found in temp of <16°C moved to deeper colder waters to occupy rocky and sandy habitats with lower food availability
