AEC 360  Ecology

Lecture 26: Mutualisms and coevolution

I.  Types of mutualisms
    A.  Dispersive mutualisms
        -- Pollination
        -- Seed dispersal

        1.  Benefit:
            -- Animals, that receive rewards of nectar,  pollen, or fruit
            -- Plants, by increasing interchange of genes,  or gene flow, through pollination
            -- Plants, by transporting seeds to sites for  germination, and away from potential  herbivores

        2.  Yucca plants and yucca moths (Fig. 17.15)
            -- Adult female moth transports balls of pollen
            -- Moths mate within flower
            -- Moths oviposit in yucca ovary larvae will eat seeds
            -- Larvae have no other food; yucca has no other pollinator
            -- Moth restrains egg laying

     B.  Defensive mutualisms
        1.  Acacias and ants   (Fig. 17.8)

    C.  Trophic mutualisms

II.   Relationships in the ant/fungus farm complex

        A.  Trophic:  involves partners specialized in complimentary ways to obtain energy and nutrients 

        B.    Defensive:  involves partners that receive food and/or shelter in return for defense 

III.  Interactions between species can drive their evolution
    A.  Mimicry
        1.  Batesian mimics are harmless, but resemble toxic species

        2.  Mullerian mimics are toxic, just like other species they resemble

    B. Reproductive mimicry

    C. Behavioral mimicry


IV.  Coevolution, evolution in two or more species as a response to characteristics of the species it interacts with

    A.  An "arms race" between species

            First observed in herbivores and their host plants
                -Some herbivores are specialists
                -Evolutionary relationships were similar between plants and herbivores

        -  Coevolution is mediated by biological agents

        -   The evolutionary effects of biological agents differ from those of physical factors in two ways:

                1.  biological factors stimulate mutual evolutionary response in traits of interacting populations
                2.  biological agents foster diversity of adaptations rather than promoting similarity

    B.  Examples

        1.  Plants and herbivores  

        2.  Flowers and pollinators