Dispersal. density and movement. Flashcards
what is dispersal?
The movement of individuals away from others, e.g. plant seeds spread away from each other and their parents.
what is the role of dispersal in regulating populations?
Emigration and immigration will decrease or increase population size respectively. Many populations are linked by dispersive individuals. Dispersal can influence competition by allowing species to occupy different regions of space e.g. plankton.
What are the three stages of dispersal?
emigration, transfer and immigration.
How is dispersal different to migration?
Migration refers to the mass directional movements of large numbers of individuals of a species from one location to another.
What are different types of dispersal?
Natal dispersal: movement between the location where the individual was bon and the place it is going to select for reproduction.
Breeding dispersal: movement between two successive breeding areas.
Passive dispersal: dispersal is non-exploratory, the destination of the dispersal is a matter of chance.
Mutualistic agent: animals eating fruit and defecating the seed away from the original tree.
Active dispersal: controlled by the individual
Clonal dispersal: common on modular organism an individual branch spreads its parts around as it grows.
What are different patters of dispersal?
Random dispersion: equal probability of an organism occupying any point in space.
Regular dispersion: occurs when an organism has the tendency to avoid other organisms or when organisms that are especially close to another die.
Aggregated dispersion: occurs when individuals are attracted to parts of the environment or by other individuals,
What is density dependent dispersal?
Dispersal depends on local population size, availability of resources, habitat quality and habitat size.
Example of inverse density dependence?
Gray-tailed vole is a common small mammals that inhabits grasslands in Western Oregon. They are polygamous, females are territorial and males have large home ranges that overlap those of several females and juvenile emigration is male based. At large population sizes a small number of individuals disperse. At small population sizes a large proportion of individuals disperse.
What is density independent dispersal?
All species that use passive dispersal by wind, gravity, currents.
What are the evolutionary consequences of dispersal?
Inbreeding avoidance occurs when close related individuals breed they are likely to suffer from inbreeding depression in fitness - favours dispersal. Outbreeding depression occurs in species that are well adapted to their local environment - long distance dispersal may bring together genotypes that are adapted to different environments, producing offspring that are adapted to neither. - force against dispersal
Philopatry - selective force against dispersal, individuals come back to their familiar environment.
What sex-related variation is there in dispersal within populations?
-sex-related differences: insect males disperse more than females - males look for females in large areas
birds - usually the females disperse (males compete for territories and females select the best)
Mammals - usually the males disperse, compete for space with most females with other males.
What age-related differences is there in dispersal within populations?
Natal dispersal: dispersal by juveniles before they mate for the first time
In marine invertebrates the larval stage is responsible for dispersal.
In insects, the adult disperses the eggs, the larva move very little.
In mammals and birds most of the dispersal is natal.
What is dispersal polymorphism?
Two or more types of dispersal structures found within a species or among the progeny of an individual. e.g. bush crickets have dimorphic individuals with and without long wings. Recently colonised populations at the range margin showed increased frequencies of dispersive, long-winged individuals, compared with longer-established populations in the range core. - short-lived because 5-10 years after colonization populations showed similar incidences of macropterous ind to populations in the range core.
Differences in dispersal distances.
Trees have low dispersal distances - seed dispersal distance for dogwood - vast bulk of seeds fall near parent tree.
What is population synchrony?
The correlation of temporal fluctuations in population dynamics between different localities
