No abstract

Understanding how species loss influences ecosystem function is a contemporary issue in ecology. However, most research has focused on species loss at one trophic-level. We explored the relationship between functional diversity (FD) and species richness separately for trees and aquatic leaf-shredding detritivores. For trees, we collected information on species-specific leaf tissue chemistry and species co-occurrences in the mid-Atlantic region (USA). For shredders, we used a published trait database with information on communities from 38 streams in the same region. We used a clustering algorithm to estimate FD for each community and for randomly assembled communities. If FD was high, we concluded that species loss was important to change in function; if low, species were functionally redundant and insensitive to species loss. We found tree FD to be significantly different than expected, but shredders exhibited FD levels similar to patterns based on random assembly. Furthermore, there were more leaf species exclusively associated with very high or very low levels of functional diversity compared to shredders. This approach revealed greater implications for leaf than shredder species loss for litter breakdown. IntroductionGlobal acceleration of species loss across ecosystems has prompted ecologists to explore how extinction alters rates of important ecosystem functions (SCHULZE and MOONEY, 1993;KINZIG et al., 2002;LOREAU et al., 2002). While there are numerous studies that have focused on species loss within trophic levels (see CARDINALE et al., 2006 for as recent review), far fewer have addressed the implications compared across trophic levels (SWIFT and ANDERSON, 1993;NAEEM et al., 1994;DUFFY, 2002;PETCHEY et al., 2004;DUFFY et al., 2007; JONS-SON et al., 2007). In detritus based ecosystems, for example, mounting evidence suggests that, in isolation, loss of resource diversity, in the form of leaf litter species loss, and loss of consumer diversity can result in substantial changes to litter breakdown rate (GARTNER and CARDON, 2004;SWAN and PALMER, 2004; LECERF et al., 2007;ABELHO, 2009). In headwater streams with forested riparian areas, both tree species loss and in-stream detritivore (i.e., shredder, sensu PETERSEN and CUMMINS, 1974) species loss are expected to have significant effects on rates of litter decomposition (SPONSELLER and BENFIELD, 2001;HIEBER and GESSNER, 2002;GARTNER and CARDON, 2004;SWAN and PALMER, 2004;KOMINOSKI et al., 2007;LECERF et al., 2007;ABELHO, 2009), which is an important ecosystem process occurring in these systems. Breakdown of organic matter describes the rate at which energy in these largely detritus based ecosystems becomes available to higher trophic levels, and the rate of organic matter export to larger, downstream waterbodies (WALLACE et al., 1982;. Since headwater streams account for the vast majority of stream miles in a watershed (HORTON, 1945;LEOPOLD et al., 1964), and are in intimate contact with the landscape as topographic low-points, understanding how spec...