Ecology: Lecture 8 Intraspecific Competition 2

Role of dispersal in mediating density-dependent 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 dispersal in mediating density-dependent 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 dispersal in mediating density-dependent 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.) Images from cirrusimage.com WinglessWinged

Role of dispersal in mediating density-dependent 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 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 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 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 metapopulations

Role of social interactions in mediating density-dependent responses  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 size: social dominance in wolves  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