The effects of foliar pubescence and nutrient enrichment on arthropod communities ofMetrosideros polymorpha(Myrtaceae)

Abstract

Abstract. 1. Nutrient resource availability and host-plant foliar pubescence both influence arthropod food webs, but multifactor studies are needed to understand their interdependence and relative importance. Arthropods were sampled by clipping foliage from Metrosideros polymorpha (Myrtaceae) trees of pubescent, glabrous, and intermediate leaf forms on fertilised and unfertilised plots.2. Fertilisation decreased leaf mass per area (LMA) but did not change the relative mass of pubescence within leaf morphological classes.3. Fertilisation increased densities of individuals in four taxonomic orders, densities of individuals and species of all trophic levels, and the biomass of Collembola and Homoptera. Herbivore relative diversity (Shannon H 0 ) also increased with fertilisation, but detritivore diversity declined due to increasing dominance of Salina celebensis (Schaeffer) (Collembola).4. Detritivore density, driven again by S. celebensis, increased with decreasing leaf pubescence, but Heteroptera and Acari were most abundant on the intermediate pubescence class, and Psocoptera density and biomass increased with increasing pubescence. Trophic-level species density did not change with leaf morphological class, but relative diversity of all arthropods and of detritivores increased with increasing pubescence.5. Both resource availability and leaf pubescence affected Metrosideros arthropod communities. However, the pervasive positive influence of fertilisation did not translate to compositional shifts, and there were no interactions with leaf morphological class. In contrast, the effects of leaf pubescence on arthropod density, biomass, and diversity were more restricted taxonomically, and nonparametric MANOVA and redundancy analyses demonstrated significant differentiation in community composition on the pubescent morphology.

Richness and species composition of arboreal arthropods affected by nutrients and predators: a press experiment

“…Previous analyses and complementary studies have shown increased arthropod abundance across all trophic levels on fertilized Metrosideros polymorpha (Gruner 2004b;Gruner et al 2005). The current study demonstrated that fertilization also increased the species load of herbivores, enemies, and all arthropods in aggregate (Fig.…”

“…Metrosideros polymorpha is variable in foliar morphology along altitudinal, edaphic, and successional gradients, and multiple pubescence classes are found within some populations (Corn and Hiesey 1973;Stemmermann 1983;James et al 2004). Three M. polymorpha morphotypes corresponding to the described varieties glaberrima, polymorpha, and incana are sympatric at this mid-elevation site (Dawson and Stemmerman 1999;Gruner et al 2005). Morphotypical pubescence on mature trees at this site did not respond plastically to fertilization, and in a separate study the community-wide effects of morphological variation were largely independent of fertilization .…”

“…Although detritivore species load did not increase in enriched plots, richness decreased significantly with fertilization. An introduced collembolan (Salina celebensis) comprised a large proportion of this response, although it was so ubiquitous that it did not cause differential changes in composition among treatments (see also Gruner et al 2005). The congeneric species Salina banksi MacGillivray can also be a numerical dominant in tree canopies of humid Mexican forests, as it was 30 times more abundant on average than all other collembolans (Palacios-Vargas and Castan˜o-Meneses 2003).…”

“…Morphotypical pubescence on mature trees at this site did not respond plastically to fertilization, and in a separate study the community-wide effects of morphological variation were largely independent of fertilization . Even so, countervailing responses to pubescence by different taxonomic groups within trophic levels may have diluted the top-down and bottom-up treatment responses seen with aggregate indices of richness, which do not account for species turnover (Hare and Elle 2002;Gruner et al 2005). …”

Understanding community structure: a data-driven multivariate approach

“…Plant species may reXect habitat architecture at a Wner scale than the architectural variables considered here; for example, leaf pubescence has been shown to inXuence arthropod community composition (Gruner et al 2005). Further, many attributes of plant communities are not species-speciWc; physiognomic characteristics of plants may be typical of a particular species but not unique to it.…”