Ecology letters paper on herbivore beta diversity on non-native plants is now out! / by Karin Burghardt

I published a few papers a couple years back with Douglas Tallamy on the abundance and alpha diversity (species at one point in space) of insect herbivores on native vs. nonnative plants (see Research for more details). One thing that always bothered me was that I hadn't yet quantified the variation in in these insect communities either among host plants or across space (beta diversity) so it was difficult to get an idea of whether alpha diversity differences are compounded or mitigated by beta diversity effect. 

I was finally able to squeeze in some time for that analysis and you can check on the results in our new paper in Ecology Letters.

The take-homes for me were that alpha diversity differences are the primary driver of differences within the herbivore communities on these plants. However, immature insects on non-native plants that aren't closely related to any native plants host a community of insects with lower host specificity among tree species than do natives. In addition these communities are more redundant across space, suggesting that widespread introductions on non-natives may lead to homogenized communities. Thus, measuring alpha diversity alone on non-native plants likely underestimates the negative impact of phylogenetically distinct non-natives on immature herbivore communities (see figure below plus figures in the paper).

 Figure 1: General diversity patterns: (a) Individual-based rarefaction curves with equivalent leaf grams sampled between treatments. This indicates that for the congeneric comparisons differences in species density between native (gold) and non-native (blue) plants are strictly abundance based (e.g. richness is lower because fewer individuals are collected for a given leaf biomass). The high abundance of adults on non-congeneric non-native gardens is primarily driven by the abundance of one species, Corythucha cydoniae (Fitch). (b) Additive hierarchical diversity partitioning into components for per tree adiversity (darkest), among tree b-diversity (b1-middle hue) and among site b-diversity (b2-lightest). These components sum to the total c-diversity of the treatment. (c) Multiplicative version isolating pure relative differentiation (e.g. b is independent of a). Here, b-diversity can be interpreted as the number of distinct units of the lower level partition and multiply to equal c-diversity (e.g. for non-congeneric non-natives, six per tree*8 among tree *1.9 among site = 91 species).  Source

Figure 1: General diversity patterns: (a) Individual-based rarefaction curves with equivalent leaf grams sampled between treatments. This indicates that for the congeneric comparisons differences in species density between native (gold) and non-native (blue) plants are strictly abundance based (e.g. richness is lower because fewer individuals are collected for a given leaf biomass). The high abundance of adults on non-congeneric non-native gardens is primarily driven by the abundance of one species, Corythucha cydoniae (Fitch). (b) Additive hierarchical diversity partitioning into components for per tree adiversity (darkest), among tree b-diversity (b1-middle hue) and among site b-diversity (b2-lightest). These components sum to the total c-diversity of the treatment. (c) Multiplicative version isolating pure relative differentiation (e.g. b is independent of a). Here, b-diversity can be interpreted as the number of distinct units of the lower level partition and multiply to equal c-diversity (e.g. for non-congeneric non-natives, six per tree*8 among tree *1.9 among site = 91 species). Source

 

Secondly, when we separate feeding guilds we see increased generalization across sites within communities (such as non-native congeners of native plants) that don't reveal differences at the whole community level. For example adult mesophyll and phloem feeders show strong negative effects on species redundancy on both on nonnative plants that do and do not share native relatives, but no difference was found at the whole community level.

 Figure 5 PCoA ordination (unconstrained) of each feeding guild community using the Raup–Crick dissimilarity (br-c) calculated across sites within native and non-native gardens. This dissimilarity uses a null model approach to condition out the impact of a-diversity on dissimilarity, a known aspect of the data set (Chase et al. 2011). Shading represents a significant effect of plant origin in PERMANOVA which tests whether the group centroid of arthropod communities on native and non-native plant species differs in multivariate space (e.g. different community composition) and a darkened black border which indicates a significant effect of origin using BETADISPER which tests whether the dispersion of a treatment from its median are different between groups (e.g. species redundancy across space) . Source

Figure 5 PCoA ordination (unconstrained) of each feeding guild community using the Raup–Crick dissimilarity (br-c) calculated across sites within native and non-native gardens. This dissimilarity uses a null model approach to condition out the impact of a-diversity on dissimilarity, a known aspect of the data set (Chase et al. 2011). Shading represents a significant effect of plant origin in PERMANOVA which tests whether the group centroid of arthropod communities on native and non-native plant species differs in multivariate space (e.g. different community composition) and a darkened black border which indicates a significant effect of origin using BETADISPER which tests whether the dispersion of a treatment from its median are different between groups (e.g. species redundancy across space) .Source

Read the whole paper:

Burghardt, K. T., Tallamy, D. W. 2015. Not all non-natives are equally unequal: Reductions in herbivore β-diversity depend on plant phylogenetic similarity to native community. Ecology Letters. PDF  or accessed at http://onlinelibrary.wiley.com/doi/10.1111/ele.12492/abstract