Ground-dwelling arthropods and environmental factors in two semi-arid habitats: Data from 1992-2004

Background/Question/Methods

Ground-dwelling arthropods, primarily predators and detritivores, for a large part of the energy flow through ecosystems, but there are few long-term studies looking at many taxa. These animals have been monitored at the Sevilleta National Wildlife Refuge in central New Mexico, a Long-Term Ecological Research (LTER) site since 1990. We report on patterns in relative abundance from 2 study sites: desert grassland and creosotebush shrubland. Arthropods were collected in pitfall traps, operated year-round and collected every 2 months. Our questions focused on factors that might influence the abundance of several family groups and that might mean for their ecological functions as climate changes. 1) Do the ground-dwelling arthropods respond to interannual changes in precipitation or other environmental factors such as temperature extremes and net primary production (aNPP)? 2) Because a number of the target taxa are long-lived, are there correlations between arthropod abundance and environmental conditions from the previous season or year (time lags)? We grouped the data into 2 seasons: winter (Nov-May) and summer (Jun-Oct), the period when the area received most of its precipitation. Precipitation during the dry periods is greatly influenced by the El Nino Southern Oscillation (ENSO).

We used canonical correlation (CCA) and regression of log-transformed abundance data to determine the most influential factors from among temperature, precipitation and aNPP. To examine changes in abundance over time we used an ordination based on Euclidean distance and a cluster analysis to produce dendrograms for the sites and seasons.

Results/Conclusions

CCA and regression analyses showed that the most important environmental factors affecting ground arthropod abundance were minimum winter temperature, the previous year’s summer precipitation, and aboveground NPP, with no association to ENSO events. CCA also showed that arthropod taxonomic families, life-history types, and trophic groups all were significantly predicted by the above climate and plant production variables.

The ground-dwelling arthropod assemblages examined in this study were relatively insensitive to climate changes lasting one or two years, such as ENSO events, but were instead surprisingly consistent from year to year despite considerable interannual change. The temperate semi-arid climate of our study area is characterized by variable precipitation and large temperature ranges, and the arthropods appear to have adapted well to the more predictable seasonal temperature changes and the long-term pattern of predominately summer precipitation. If climate change alters these cues, changes in ground arthropod taxonomic composition and abundance may follow, with important implications for changes in ecosystem function.