Chapter 13: Interactions among Species

intimate associations between species that may be either mutualists or parasite and host

reciprocal genetic change in interacting species, owing to natural selection imposed by each on the other. Not all adaptations of one species to other species are necessarily coevolved

two species evolve in response to each other; Angraecum orchid and its specialized pollinating moth

several species are involved and their effects are not independent; genetic variation in the resistance of a host to two different species of parasites might be correlated

a species evolves a defense against enemies and is thereby enabled to radiate into diverse descendant species, to which different enemies may later adapt

the vertebrate immune system, which can generate antibodies against thousands of foreign compounds

an elaborate system of recognizing and defending against foreign invaders—that is, viruses

each species has to run (i.e., evolve) as fast as possible just to stay in the same place (survive) because interacting species also continue to evolve

also called escalation; greater speed of gazelles and of pursuit predators such as cheetahs; n lead to extinction or to a stable point when the costs of increasing the trait (e.g., speed, or a plant’s defensive chemicals) become too great

evolved warning coloration; bright colors that signal to a potential predator that they are distasteful or dangerous

form of convergent evolution in which resemblance between different species has evolved because it is advantageous for members of one species to resemble another.

based on the aposematic coloration of other species

a palatable species (a mimic) resembles an unpalatable species (a model)

two or more unpalatable species are co-mimics (or co-models) and jointly reinforce aversion learning by predators; the mimic that matched the locally abundant model survived best

they play little or no role in primary metabolism

proposed a scenario of escape-and-radiate coevolution, in which a plant species that evolves a new and highly effective chemical defense may escape many of its associated herbivores and give rise to a clade of species that share the novel defense

Parasites that reduce the survival or reproduction of their hosts

based on interactions between some plants and fungal pathogens

a pathogen can infect a host only if it has a protein that matches a cell surface receptor protein of the host, like a key and a lock

Ellen Decaestecker; e Daphnia population underwent genetic change from year to year and that the bacteria evolved in concert, as in matching allele models of coevolution.

Daphnia magna produced more spores and caused greater mortality when infecting hosts from their own or nearby populations. This suggests that the parasites are best adapted to their local host population, leading to a more severe impact on sympatric host populations.

important for maintaining resistance to pathogens

arose from a virus that infects cats and several other carnivores; After the virus first entered the dog population, several additional evolutionary changes made it more effective at binding the dog receptor and unable to bind that of its original feline host

interactions between species that benefit individuals of both species

a genotype that “cheats” by exploiting its partner without paying the cost of providing a benefit in exchange is likely to have a selective advantage

although species arising from a common ancestor will at first be very similar, natural selection will make them more different, because “the more diversified the descendants from any one species become in structure, constitution, and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature, and so be enabled to increase in numbers.

occurs within a single species, where individuals of the same species compete for the same resources such as food, water, shelter, or mates.

involves competition for resources between different species that utilize the same resources in an ecosystem

1. , two (or more) competing species that use exactly the same resources cannot coexist indefinitely: one will be driven to extinction.

2. competition can impose selection on one or both species. One of the possible results is divergence in resource use.

divergence in response to competition between species

a species or population exhibits greater variation in resource use, and in associated phenotypic characters, if it occurs alone than if it coexists with competing species

individuals suppress competitors by behavioral dominance or by other means, such as poisoning them

assemblage of species in a local habitat, such as a lake or forest

what determines how many species occur together in a local community, how food webs and other interactions among species are structured, and why the number of species differs among habitats and geographic regions

Convergent morphologies

two regions have similar environments, we might expect to see convergent evolution not only of individual species but of assemblages of species