Walker, Sarah by lev17755

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									                                         Walker, Sarah
                                  Whose legs are in the water?
        Parsing out community composition and turnover rates of
              Plecoptera, Trichoptera, and Ephemeroptera
                          Faculty Mentor: C. Riley Nelson, Department of Biology

Many beta diversity indicies, like most analytical tools in ecology, abstract the known relative
abundances and species presence into outputs primarily useful for obtaining p-values and little
else. Therefore, the purposes of this proposed beta diversity method were to simplify currently
used similarity analyses for visualization and quantification of beta diversity, investigate its use
in seasonal succession and other gradients in communities, and demonstrate an application of
these methods in terms of both taxonomic and functional richness.

Materials and Methods: From 2003 to 2007, the American Fork River in central Utah was
sampled for terrestrial adult forms of aquatic macroinvertebrates. With emphasis on the 2004
component of this data set, I developed a simple method to assess time or place of community
turnover along a temporal or spatial gradient using similarity indicies. Initial development of
these ideas was inspired by communication with Dr. John Longino of Evergreen State College.

Construction of so-called Sierra plots1 is fairly straightforward in that a matrix is composed
giving the Morisita-Horn or Chao-Sorenson similarity values for each site as it relates to each
other site, including each site‟s similarity to itself which is 100% or a value of 1. From this
matrix, a line graph is composed treating each site (or date) as a line or data series, thereby
charting its similarity to each other site as well as the rate of turnover between each site or
sample. The slope of the similarity lines composing Sierra plots are important for
determining rates of community turnover, or beta diversity. Slopes were calculated for each
segment of the line to assess rates of change between sites or dates.

In order to further assess similarities between sites and samples, Non-Metric Multidimensional
Scaling (NMDS), Similarity Percentages (Simper), and Analysis of Similarities (ANOSIM)
analyses were conducted using Primer 6. The Bray-Curtis similarity index was selected for use in
comparisons. Factors including month the samples were taken in, proscribed plateau community,
which site the sample was collected at, and dominant character states for functional traits were
entered as variables to assess influences on similarity. To assess changes in functional trait
structure of the community, two-way nested ANOSIM analyses were performed with the specific
trait in question nested within either site or month classification. ANOSIM outputs were used as
additional analyses because this method is currently common in the literature and would
therefore provide a comparison to Sierra plot findings.


1
 Longino, J. T. 2006. Richness and faunal turnover of ants (Hymenoptera, Formicidae) on the Barva Transect. Entomological
Society of America Meetings. Indianapolis, IN.; Longino, J. T. 2007. Personal correspondence (email). October 24, 2007.
         Results: Beta diversity measures using Sierra plot slopes are indicative of community
         turnover rates between sites. The sharpest rate of change occurs between Site 2 and 3
         (Fig. 1) which are, counterintuitively, closest in both elevation (44 m difference) and
         distance (2.49 km difference). The transition between Sites 2 and 3 is 9.686 to 13.554 times
         greater than change between other sites. Results were similar when using the Morisita-Horn
         index and either species or family groupings . Functional traits, particularly voltinism and habit
         type, and trait richness also followed this trend of sharp turnover between sites 2 and 3.

         Seasonal community changes, also visualized by Sierra plots (Fig. 2), show three prominent
         communities that consistently occur over the course of each year and at each site. Some variation
         occurs in phenology of the plateaus, but most are centered around dates in April (“Winter”), June
         (“Spring), and August (“Summer”). Plateau communities were also supported by clustering
         analysis performed using Primer 6.

         Functional traits, as measured by the dominant character state of a sample, differed across time
         with little correlation to turnovers in species or family richness. Trait richness, as examined by
         treating each functional trait as if it were a species, showed one community turnover between
         June and July (Fig. 3). This preceded a turnover of the same samples in taxonomic richness, both
         family and species, which occurred in July. These communities delineated by taxonomy also
         experienced an earlier turnover in June which the functionally defined community did not.

         Individual traits exhibited different seasonal patterns. Both trophic groups and habit types
         showed a strong turnover between May and July (Fig. 4). However, life cycle strategy and
         development rate both had a strong turnover in mid-June. Interestingly, voltinism was highly
         variable from April to May but then had a strong plateau community thereafter. Other traits such
         as size and drift mobility also had interesting turnover patterns.

         Discussion: The appearance of what I have termed „plateau communities‟ was an unexpected
         result of a large study intended to survey the aquatic insect community of the American Fork
         River in Utah. The formation of a cohesive seasonal community opens questions about
         community structuring. Why, for instance, do certain species occur together and in what ways to
         they overlap functionally? Additionally, how do the species within a plateau community relate
         ecologically and evoluationarily? And do different plateau communities exhibit similar
         functional structure and do what degree?

         The discipline of ecology, currently dominated by NMDS plots and clustering analyses, can
         benefit from investigating new and simpler approaches to analyze community turnover that are
         more accessible to students, researchers, and conservationists alike.
         Figure 1.                                                     Figure 2.                                                                                                                                                                             Figure 3.                                                                                                                                Figure 4.
         Elevational Sierra Plot.                                      Seasonal Sierra Plot.                                                                                                                                                                 Trait Richness Sierra Plot                                                                                                               Trophic Sierra Plot.
         Note turnover from 2 to 3.                                    Plateau communities circled.                                                                                                                                                          Turnover precedes expected.                                                                                                              Turnover parallels habit trends.
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