Host Plant and Spatial Influences on the Natural Enemy Community Structure of a Host Specific Insect Herbivore
Date
2018-05
Authors
Busbee, Robert Waid
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Abstract
Both environmental variation and spatial autocorrelation play roles in structuring
communities at all spatial scales. However, untangling the respective contributions of
these sources of variation represents a long-standing, complex, and methodologically
ever-evolving question for community ecology. Here I investigate the structure of the
insect natural enemy community centered on galls produced by Belonocnema treatae
(Hymenoptera: Cynipidae) on the leaves of its host plants across the gall former's
geographic range while controlling for spatial autocorrelation among sample sites.
Belonocnema treatae exhibits regional host plant specialization across the southern US
on three live oak species, Quercus fusiformis (Qf), Quercus virginiana (Qv), and Quercus
geminata (Qg). I sampled the natural enemy community at 94 sites by rearing natural
enemies that emerged from galls collected at each site. I identified 32,722 natural
enemies representing ≥30 taxa from 126,812 galls. I hypothesized that richness and
diversity on Qv would exceed that on Qf and Qg since the geographic range of Qv bridges
that of Qf to the west and Qg to the east. Contrary to my hypothesis one-way ANOVA
followed by a Tukey’s HSD showed that both richness and Shannon-Wiener diversity
was greatest on Qf. To disentangle the role of host plant affiliation from spatial
autocorrelation among sample sites I conducted a Redundancy Analysis (RDA). I first
used Principal Coordinates of Neighbor Matrices (PCNM) to generate explanatory
variables representing orthogonal aspects of spatial structure within the sampling frame.
The set of PCNM vectors that were significantly correlated with community structure were then included in a RDA along with the host plant species from which each natural
enemy was reared to examine the respective roles of host plant association and spatial
structure in determining abundance and species composition of the natural enemy
community. This study establishes a significant role for both alternative host plants and
geography in structuring the diversity of the natural enemy community of B. treatae and
illustrates the advantages of the PCNM & RDA approach.
Description
Keywords
Conservation biology, Ecology, Host plants
Citation
Busbee, R. W. (2018). <i>Host plant and spatial influences on the natural enemy community structure of a host specific insect herbivore</i> (Unpublished thesis). Texas State University, San Marcos, Texas.