Ecology: Lecture 8Ecology: Lecture 8

Intraspecific Competition 2

Role of Role of dispersaldispersal in in mediating density-mediating density-

dependent responsesdependent responses Potential benefits to dispersers

(individual fitness) Higher growth rates. Why? Higher fecundity. Why? Outbreeding

New genetic combinations & increased heterozygosity of offspring

Always a benefit? Avoid competition with kin

Combined inclusive fitness may be higher What does inclusive fitness include?

Role of Role of dispersaldispersal in in mediating density-mediating density-

dependent responsesdependent responses Potential costs to dispersers

(individual fitness) Greater risk in movement (↓ food & water,

predation, unfamiliarity with terrain) Inability to find suitable habitat Individual not as well-adapted to new

environment Outbreeding depression (disrupt co-adapted

genes) Offspring less adapted to the environment

Loss of kin associations Loss of adaptive social traditions

Role of Role of dispersaldispersal in in mediating density-mediating density-

dependent responsesdependent responses Benefits of dispersal depend upon current

level of competition In some species, young adults cannot find breeding

territories or mates unless they disperse (i.e. male lions) Some species adjust dispersal depending upon

population density Example: water striders (Gerris spp.)

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Wingless Winged

Role of Role of dispersaldispersal in in mediating density-mediating density-

dependent responsesdependent responses

Effects on populations Can establish new populations within a

metapopulation ↓ vulnerability to extinction. (Why?

How will the genetic make-up of the new population compare to the original population? Founder effect… But what if dispersers to new location

arrive from multiple source populations?

Types of dispersalTypes of dispersal

Pre-saturation dispersal At what population densities does this

type of dispersal take place? Below K/2 (density-independent)

Which individuals disperse? Both genders Healthy individuals in their prime Genetically-based subset?

Types of dispersalTypes of dispersal

Saturation dispersal At what population densities does this

type of dispersal take place? Above K/2 (density-dependent)

Which individuals disperse? Juveniles and subdominants (Why?)

Sink habitatsSink habitats

Organisms permanently removed from the source population

Unable to sustain itself (d>b) Example: Conch populations in Florida

Is it possible for sink habitats to have high population densities?

Queen conch Queen conch metapopulationsmetapopulations

Role of Role of social interactions social interactions in in mediating density-dependent mediating density-dependent

responsesresponses Social dominance determines who

will have the best access to limited resources

What type of competition is this and why? Contest competition: dominants achieve

relatively high levels of fitness at the expense of submissives when resources are limited.

How can population size be regulated by social dominance?

Social dominance is more pronounced for high-density populations (Example: wolf populations)

Regulation of population Regulation of population size: social dominance in size: social dominance in

wolveswolves Packs consist of relatives,

with male and female hierarchies

The alpha (and sometimes beta) male mates with the alpha female. Only the alpha female has young. All pack members cooperatively

raise young. Packs become larger when

population densities are high Fewer alpha and beta individuals Fewer offspring

Packs break apart when population densities are low More alpha and beta individuals More offspring produced at low

density.

Photo courtesy of NOAA