Use of space: Dispersal, migration, cues

What is dispersal?

• ecological process affecting distribution

• leaving an area of birth or activity

• usually a once in a lifetime event → movement to a new habital

• usually a short range but can also belong range

Active dispersal

movement from one location to another by its own means

Passive dispersal

movement from one place to another by means of a stronger force, such as water flow, wind, or another organism

Why disperse? There are 2 choices

1. Stay at home and produce a few descendants

2. take a chance to colonize a new area and leave many descendants

What kind of dispersal is favoured by natural selection?

Natural selection favours individuals that move a modest distance from their birth place

This prevents competition, including with parents and siblings

If colonization is successful, dispersal will result in gene flow and/or a founder effect, and thus affect the genetic structure of a population

Sex-based dispersal

kin avoidance mechanism

Because dispersal entails costs, both sexes of progeny need not disperse to dramatically lower the probability of inbreeding

Crowding dispersal

competition-reduction mechanism

On average, individuals in the low-density treatment dispersed shorter distances than those in high - density treatment

Benefits of dispersing

• Reduce intraspecific competition

• Inbreeding avoidance

• Find more suitable habitats

• escape unfavourable conditions

Costs of dispersal

• Energy, risk, time, and opportunity

• Outbreeding depression if better adapted to natal habitat

• lack of local familiarity

• for invasive species, Benefits greatly outweigh the costs, so invasives are highly tolerant & flexible

Ecological dispersal

movement of individuals away from an existing population or parent organism

adaptive role in life history of organism

Biogeographical dispersal

species shift their range by moving over long distances across large barriers (broader spatiotemporal scales)

Barriers to dispersal

• The nature of long-distance dispersal means that animals often have to survive for periods of time in environments that are hostile to them

• These environments constitute physical and biological barriers to dispersal

• Preventing dispersal depends not only on the nature of the barrier, but also on the species dispersing

physical barriers

• Encounter physical obstacles

• Unfavourable environmental conditions (transient or permanent)

• nature of barriers can change with the season

• nature of barriers can differ among similar species

Physiological Barriers

• created by environmental conditions which individuals are unable to survive long enough for dispersal

• conditions are therefore outside the range of tolerance

ecological barriers

predators and competitors can restrict animal movement

• consumptive an non-consumptive effects

• exploitation competition

Behavioural Barriers

Some animals exhibit limited ability / willingness to disperse across barriers

In order to expand its range through dispersal, an animal must be able to:

1. Reach a new area.

2. survive the potentially harsh conditions occurring during the passage.

3. Survive and reproduce in the new area to the extent that a new population is established.

what are the three types of dispersal events? (they are all biogeographical)

1. Jump dispersal

2. Diffusion

3. Secular dispersal

what is jump dispersal?

the colonization of new areas by individuals over long distance and over habitats that are inhospitable.

• Certain organisms, possessing certain traits – flexibility, wide tolerance range – are more likely to be successful.

• Long-distance dispersal likely has a selective component.

what is diffusion?

the slower spread of of individuals outward from the margins of a species’ range.

• It is a slower form of range expansion involving movement into adjacent habitats as population expands

what is secular dispersal

occurs much more slowly. So slowly, in fact, that organisms can evolve enroute during the process

• Although the geographic range is expanding, natural selection is causing migrants to diverge from the ancestral population.

what is migration?

• A form of dispersal which involves movement away from, and subsequent return to the same location, typically on a periodic basis

• To migrate long distance animals must navigate through the environment and use cues to assess where they are in relation to where the are heading.

characteristics of migration

• periodicity (daily, monthly, annual, generational)

• round-trip

• active movement by the individual

• persistent direction

• initiated based on environmental triggers

• often involves specialized physiological changes

why migrate?

• Food / water (track ephemeral resources)

• Climate (less chance of experiencing environmental extremes)

• Mating & birthing (better environment for eggs, young)

• geologic history (constrained / unchanged through evolution)

benefits of migration

• Exploit seasonal food sources

• Special conditions for breeding

• Reduction in competition for resources

• Reduction in predation for vulnerable life-history stages (eg. calving grounds)

• For rest / overwintering

costs of migration

• Energetic investment with little opportunities to feed

• Development costs – i.e., navigational systems

• Risk of predation during movement

• risk of hazards

facultative migration

Individuals of the same species can choose to migrate one year and not the next

• depends on prevailing food supplies, weather conditions

• resources vary unpredictably

• conditional strategy based on reserves, age

• adaptive response

obligate migration

There are innate (programmed) components to migratory navigation. This genetic component of migratory orientation is heritable

what is navigation?

Processes that enable an animal to find its way from one specific place to another.

An animal can use different navigational mechanisms for different distances from the target, and different orienting cues for different environmental conditions.

what is piloting?

the ability to find a goal by referring to familiar landmarks

• precise location in limited area

what is Compass orientation?

the ability to head in a geographical direction without the use of landmarks and by using cues

• innate

what is True navigation?

aka dead reckoning

reference to a goal is established regardless of its location without familiar landmarks or the need for cues.

homing (another word for dead reckoning)

• Some animals can return home after being displaced to unfamiliar territory

• Process of continuously updating information about the distance and direction travelled, in order to compute the vector to a desired location

• requires cognitive map + compass cues

types of cues in navigation

• Celestial compass (sun and polarized light)

• Stars

• Geomagnetic field (magnetosense in brain and eyes)

• Visual (landmarks, shore lines, sea mounts)

• Olfactory cues

• self-movement

methods of tracking animals

1. mark and recapture

2. genetics

3. stable isotopes

4. radio or acoustic telemetry/satellite tracking telemetry

5. data collection systems