The Curious Case of the Termites: How Rainfall Affects Diversity in the Australian Tropics Open Access
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Termites are critical components of tropical systems where they are thought to decompose up to 50% of plant organic material in litter, wood and soil. Termites have adaptations (e.g., the ability to scavenge and store water in their mounds) allowing them to thrive in habitats with variable rainfall and remain active during droughts. One frequently drought-affected area, the Australian tropics, is thought to show a unique pattern of termite distribution, with termite diversity and abundance lower in rainforests, peaking in drier savannah ecosystems. This pattern, if true, is opposite to what is found in tropical regions around the globe where termite diversity and abundance is highest in rainforests. Our study aims to survey termite turnover across a precipitation gradient and examine the causes and consequences of this anomaly. In five sites in Northern Queensland ranging from 600--5000 mm annual rainfall, we collected samples from 50 m transects and 50 m x 50 m plots and measured termite abundance and diversity, deadwood occupancy, and termite mound abundance. We analyzed turnover of feeding types and landscape types among sites with differing rainfall. We observed dramatic decreases in termite abundance in both mounds and deadwood corresponding to an increase in rainfall (107 mounds per 1/4 hectare plot in the driest site, compared to 1 mound per plot in the wettest). Of the 18 termite species encountered in this study, none were soil feeders; litter and grass feeding termites were found only in the savannah sites, while wood feeders were found in both rainforest and savannah sites. These results support the termite diversity anomaly and point to turnover in feeding guild with greater diversity in savannah, suggesting that part of the anomaly lies in the adaptations to food resources across habitats. We found that presence of several common species of termites including Amitermes laurensis, Nasutitermes magnus, and Microcerotermes cerratus, corresponded more closely with habitat type than with distance from other sites. These results suggest that termite communities assemble in large part based on habitat type. Rainfall is an important factor in termite community assembly shaping the termite diversity distribution although why so few termites are found in the rainforest remains elusive.
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