Question about last week: why talk about introduced and invasive species?

(food plants, rubber, chocolate, oil palm; weeds: environmental modification, control expenses)


"Survival of the fittest" doesn't necessarily mean the biggest, most aggressive, most voracious, etc. Cooperation can be an evolutionary adaptation.

Five types of interactions among species:

  1. Harm both - competition e.g. feeding on same food plant
  2. Benefit self, harm other - predation, parasitism e.g. numerous examples
  3. Benefit both - mutualism e.g. plants and nitrogen-fixing microbes, ants and acacias, ants and Cecropia (etc.)
  4. Benefit self, other unaffected - commensalism e.g. cattle egrets
  5. Harm other, self unaffected - amensalism e.g. ............................ ?

All of these interactions provide opportunities for coevolution (but coevolution does not always occur)

Interactions can be diffuse (among groups of species, e.g. plants and herbivorous insects) or specific (among two or a few species)


Competition: Ecological -> competitive exclusion (Gause) -> niche partitioning

Evolutionary (involves genetic change over time) -> niche differentiation

Predation, parasitism, pathogens:

Ecological -> population regulation, local extinction

Evolutionary -> "evolutionary arms race"

Mutualism: Ecological -> distribution and abundance may be linked (strict)

Evolutionary -> may evolve physiological interdependence (e.g. mitochondria, chloroplasts, gut flora e.g. humans, termites, algae/coral, lichens)

Examples of Coevolution


Diffuse: fruit colors and avian dispersers,

Diffuse or specific: herbivores and plant defensive compounds

Specific: numerous plant-pollinator relationships (e.g. orchid/hawkmoth, wasp/orchid, weevils/seeds); ant/acacia


Diffuse: ............................?

Specific: many host/parasite relationships, ant/lycaenid larvae, ant/aphid

Multiple trophic levels

Figs, fig wasps, nematodes - specificity, congruent phylogenetic trees


Batesian - palatable sp. mimics noxious sp. e.g. viceroy/monarch, moths that mimic wasps

Müllerian - convergence in appearance of noxious species, e.g. Heliconius butterflies, various bees and wasps.