Tropical arthropods represent a significant fraction of biodiversity and play major roles in ecosystem function, yet the theory and practice of assessing their response to anthropogenic disturbance remains poorly developed. In addition, recent studies indicate that arthropod populations are rapidly responding to current human-driven climate change with modifications in phenology, distribution, and species interactions. Significantly, arthropod response has also been stronger than in other groups of organisms, such as plants. However, adequate monitoring schemes for multitaxic assemblages of tropical arthropods are currently lacking.
The Arthropod Initiative of CTFS - ForestGEO aims at long-term monitoring of key arthropod assemblages and studying insect-plant interactions over our forest network. The initiative integrates with ongoing monitoring of plant dynamics within the network, causes minimum possible impact to the plots, and focuses on a priority set of assemblages chosen for their ecological relevance, taxonomic tractability, and ease of sampling. These assemblages include mainly:
- termites (decomposers)
- selected moths, butterflies, and their caterpillars (herbivores, pollinators)
- tephritid fruit flies (fruit feeders)
- litter-dwelling ants (various roles)
- bees (pollinators, pollenophages)
- selected parasitoids
- seed predators
At each participating CTFS site, the first year of the program is devoted to a baseline survey that serves several purposes, notably, to refine the methodology and the definitive choice of assemblages. This baseline survey involves replicated, repeated sampling programs using a mixed set of procedures. The baseline survey is followed by longer-term programs of field work and analysis, organized into two main sub-programs: monitoring and key interaction studies. The monitoring sub-program is directed to detect long-term changes, as reflected in priority assemblages, driven by climatic cycles, climatic change, and landscape-scale habitat alteration. Monitoring protocols are derived from those used during the baseline survey. The food-web approach of interaction studies will involve rearing insects feeding on a small subset of local plant species (such as ten focal tree species), as well as associated seed predators and parasitoids. When deemed appropriate, a new subset of focal plant species will be chosen, expanding progressively the study system and the ecological knowledge of CTFS plots.
Since adults are easier to survey than juveniles, the monitoring scheme targets adults, surveyed by traps. Since juveniles are often more intimately associated with plants than adults, interaction studies focus mainly on juveniles reared from focal plant species. The baseline survey, reference collections, and barcoding library help to match juveniles with adults. In short, the CTFS Arthropod Initiative targets common species that are well collected with methods that can be applied consistently over the network. This is reasonable, as rare species are not amenable to statistical analysis of long-term monitoring trends.
Click here to download a concept note related to the Arthropod Initiative.