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Mutualism and Commensalism/ Coevolution BIOL400 5 October 2015 Commensalism and Mutualism Commensalism Close association of two species that benefits one, without benefiting or harming the other Exs: Birds nesting in trees Epiphytic plants (bromeliads, poison ivy, etc.) Barnacles attached to whale heads Algae on turtle shells Mutualism Close association of two species that benefits both Mutualism Categories 1) Trophic—both species derive nutritional benefit Exs: Ants and acacias (Fig. 12.6 p. 217) Fungi and algae in lichens Mycorrhizae and trees Fig. 12.6 p. 217 p. 217 Figs. 12.21& 12.22 p. 228 Douglas fir seedlings in sterilized soil, with areas “contaminated” with fungal spores Mutualism Categories 2) Defensive/Cleaning—one species benefits from cleaning by another (also partly trophic) Exs: Cleaner fish Screech owls and blindsnakes Mutualism Categories 3) Dispersive—one species benefits from dispersal of its reproductive products (also partly trophic) Exs: Pollen Seeds (fruits, elaiosomes) Spores (certain mosses, fungi) Keystone Commensals and Keystone Mutualists Species whose roles in commensal or mutualistic interactions greatly affect community structure “Pulling” the keystone would cause the ecosystem to change dramatically Gopher Tortoise of SE U.S. Up to 100 feet of burrows maintained by one tortoise at any time Periodically abandon burrows to dig new ones 350 other species use gopher tortoise burrows At least one (the indigo snake) is threatened by declines in gopher tortoise numbers American Alligator in the Everglades, FL Dig “gator holes” as retreats during hottest part of day May be only standing water during severe droughts Fig Wasps and Fig Trees Wasps are pollinators Numerous species (such as this emerald toucanet) rely on fig masting as periodic food supply Coevolution Coevolution Reciprocal selective forces of two species on one another Evolutionary adaptive responses of each species to the other May concern • • • • Physiology Anatomy Behavior Life-cycle attributes Fig. 2.11 p. 27 Coevolution in Mutualism Coevolution is a necessary part of mutualistic interactions Ex: physiological, anatomical, and behavioral adaptations of ants and acacias Ex: same, in a pollination relationship Close examination also demonstrates antagonism in these interactions Selection wouldn't have it any other way! Antagonism in Coevolved Mutualisms Producing not enough nectar to satiate is selected, as opposed to producing enough to satiate Delaying fruit ripening until seeds are fully developed Species May Take Advantage of Mutualistic Interactions Fish that resemble cleaner fish but sneak bites from the mouths of larger fish Orchids that have labella that resemble female bees Coevolution and Competition Coevolution and Competition Species that compete for limited resources can coexist if their degree of overlap is small enough, i.e., by partitioning the resources Character displacement: divergence of a characteristic related to resource use in areas of geographic range overlap Fig. 10.22 p. 182 Clearest when A) each of the sympatric species also has an area of allopatry B) the two species are quite similar in both resource use and the character related to it in their respective allopatric portions of their ranges Fig. 10.23 p. 183 Fig. 10.24 p. 184 HANDOUT—Moen and Wiens 2009 HANDOUT—Losos and de Queiroz 1997 Difficulty in Proving Character Displacement Character displacement is an historical process Stringent requirements for establishing it has occurred: —At least partial allopatry (no evidence is possible if sympatry is complete) —Heritability (often assumed without certainty) —No other unrelated reason for the divergence in sympatry —The two species must actually compete (resources must be limiting) Coevolution and Predation Coevolution in Predator-Prey Relationships Often compared to an arms race, with adaptation and counter-adaptation Prey Defenses (Predator Counteradaptations) Anatomical Thorns Spicules Quills Armors (Giraffe tongues) (Hawksbill turtle intestinal lining) (Fishers) (Gulls/bivalves) (Starfish stomachs/oysters) (Jaguar jaws/tortoises) HANDOUT—Meylan 1988 Prey Defenses Chemical Plant “secondary compounds” Bombardier beetle Skunks Salamandra salamandra Various toads and frogs Monarch caterpillar Fig. 12.1 p. 211 & Table 12.1 p. 212 Fig. 12.3 p. 214 47 tree spp. in Panama Fig. 12.4 p. 215 Toxins may be produced only in response to herbivory More toxins may be produced in most valuable plant organs Prey Defenses Behavioral Hiding Running Aggressive defense Group living Cryptic Coloration Coloration that may make an animal blend into its environment Exs: Peppered moths Kenyan chameleon Spring peeper Disruptive Coloration Coloration that confuses predator against environmental background Exs: Zebras Garter snakes Aposematic Coloration Warning coloration associated with toxicity or other chemical defenses Exs: Skunks Dendrobatid tree frogs Mimicry Batesian: Palatable/nonvenomous species mimic unpalatable or venomous species Mullerian: Similarity among unpalatable or venomous species Eyespots—provide startle effect Cryptic mimicry—Prey (or predator) resembles inanimate object of its environment Fig. 11.22 p. 206 Left: Venomous Micrurus Right: Nonvenomous Pliocercus Coevolution and Parasitism Coevolution and Parasitism Van Valen's Red Queen Hypothesis is another form of the arms-race concept Pathogens become more virulent, but selection rapidly spreads any infection resistance a host population has In the wild, infections tend to be less virulent over time Fig. 15.21 p. 277 No evolution of mice Experimenter used inbred genetic strain Typhoid bacterium is winning a one-sided arms race