Exploring the Possible Relationships between Terrestrial Arthropod and Plant Community Structures in the South Texas Plains
The South Texas Plains is one of many locations worldwide that has rapidly changed from grass-dominated rangeland into a relatively densely wooded thicket; a mechanism of succession termed the “mesquite-nucleus hypothesis,” which states that a mesquite tree is well evolved to encroach on grassland and change the micro-habitat, thereby allowing other woody species to encroach more easily, has been proposed. The current study tests the mesquite-nucleus hypothesis by studying arthropod community structure and its relationship to the surrounding plant community structure. Arthropods are easily trapped and counted, but complete survey data for South Texas is sparse. Pitfall traps were used in three distinct transect lines to collect arthropods between 19 September 2015 and 31 March 2016. Most arthropods were identified to the order level, spiders were identified at the family level, and ants were keyed to the genus level. Relative abundances, direct comparisons of relative abundances, Simpson indices, Shannon indices, G-tests of independence, richness extrapolation, and richness estimation were used to compare arthropod community structure among the transect lines, and the point-centered quarter method was used to characterize plant communities and place traps. The mesquite-nucleus hypothesis is weakly supported by some of the data, but experimental replicants are needed. Overall, evenness and diversity were highest in the mesquite transect, but the transect dominated by blackbrush had the highest arthropod abundance. The relative abundance data for several taxa raise questions that should be further investigated: Diptera abundances seem negatively correlated with the average distances between shrubs or perhaps prefer to be near blackbrush, Salticids were found to prefer blackbrush, and Gnaphosids were disproportionally present in the transect referred to as mixed. Ant communities were similar among transects.