AEC 360  Ecology

 Biodiversity and Ecosystem Functioning

I.  Why does biodiversity matter?

II.  What services do ecosystems provide humans?

III.  What are the effects of biodiversity on ecosystems?
    A.  Early ecologists and biodiversity
        1.  Ecologists have long been interested in factors that control the diversity of species
        2.  Elton (1950s) proposed higher diversity = higher ecosystem stability
        3.  Observed that higher diversity led to higher productivity, reduced invasions, lower severity of disease or pest outbreaks

    B.  Parallels to studies from agriculture

    C.  Recent experiments on biodiversity -- Cedar Creek Natural History Area

        1.  Experimental design and maintenance

        2.  Higher diversity of plants led to higher plant productivity
            -  What causes this relationship?

                -More diverse ecosystems are likely to contain the most productive species (Sampling effect)
                -Interactions between species allow them to use resources that could not otherwise be use (Fig. 17.22)
                -Different species are likely to take advantage of resources in different ways (Niche differentiation)

        3.  How does lower diversity of plants influence consumers, like insects?
            -- Disease and insects move to and remain on monocultures of their food plant (Resource Concentration Hypothesis)
            -- Predators prefer diverse habitats (enemies hypothesis)
            -- Both of these factors would lead to lower pest abundances at higher levels of plant diversity

        4.  Higher plant diversity causes less plant disease and lower insect abundances

        5.  Higher plant diversity causes higher diversity of consumers

             -- Plant species richness increases insect species richness each year…but patterns are weak

             -- Plant species richness has its strongest effects on cumulative insect diversity

        6.  Higher diversity leads to fewer invasions

    D.  What is the relationship between diversity and stability of ecosystems?

        1.  What is stability?

        2.  In one experiment, higher plant diversity increases the stability of insect population and communities

        3.  Why are more diverse ecosystems more stable?

            - The average fluctuation of many species combined is lower than fluctuations of individual species
            - Competitive effects – rise in production of one species leads to decrease in other
            - Diverse assemblages contain species that each perform best under different environmental conditions

        4.  The Cedar Creek experiment shows that in diverse plots, stability of ecosystem production is higher (even though biomass of individual species fluctuates more)

IV.  Conservation implications
        - Importance of biodiversity to ecosystem function
        - Importance of single species to ecosystems
        - Effects of exotics