Tetiaroa Society Ecostation

05 Jul, 08 AM - 02 Aug, 02 PM

As the Tetiaroa Society is scheduling the eradication of rats from of all the motus of Tetiaroa for August 2021, we would like to set up monitoring over the next several years to follow the effects of rat removal on the functioning of insular ecosystems. Our project would especially focus on the consequences of rat removal on two faunal groups within these island ecosystems: seabirds and crabs. Both groups are critical to these ecosystems; seabirds due to the nutrient inputs they provide, and crabs because of their important role as terrestrial omnivores (a role currently filled by rats). We will of course aim at adjusting our protocols and objectives to complement, rather than overlap, with the protocols that have already been settled by other teams. We will first aim to better understand the direct effects of rats on these ecosystems by measuring predation risk to birds, crabs and seeds on invaded, previously invaded, and uninvaded motus. By using plasticine models and cameras, we will also determine predator identity (e.g., rat vs. crab). Note that, although the predatory effects of rats have been investigated in varying degrees, it is often difficult to predict how the cascading effects of rat invasion may have influenced overall predation risk. For example, eggs may be frequently consumed by rats on invaded islands, but less frequently consumed by crabs. Such cascading consequences of rat invasion on food web dynamics remain poorly understood. We will therefore aim to complement the current data on crab densities with direct measurements of predation risk across motu that have never had rats, were previously invaded by Polynesian rats, are currently invaded by Polynesian rats, and are currently invaded by both black and Polynesian rats; we will then compare predation risk across these islands pre- and post- eradication to obtain an integrated view of how rat invasion influences predation risk in these ecosystems. In addition, we will investigate how rat removal indirectly affects terrestrial insular ecosystems via influences on seabird populations. As predation risk to birds decreases following rat removal, seabird densities are expected to increase. The guano-derived nutrient inputs that accompany these population increases can frequently have strong effects on island ecosystems. We will therefore finely quantify nitrogen inputs from seabird guano by taking detailed measures of bird abundance and defecation rates, as well as using stable isotopes to track these inputs through the soil, leaves, and forest floor fauna (i.e., crabs, spiders, and lizards). As seabird densities vary throughout the day, throughout the year, and across years, this will require repeated monitoring. In addition, we will track changes in litter decomposition rates and litter depth, which may occur in response to nutrient inputs or due to changes in faunal/floral assemblages (e.g., increased crab or palm densities). Finally, we will characterize the microhabitats used by the different bird species and identify appropriate habitats that may not be currently used because of the rats. This should have implications in terms of predicting where birds may settle post rat-removal. In addition, this information could be subsequently used to help inform habitat restauration efforts, both in Tetiaroa and globally. The latter aspect will be developed in collaboration with Prof. Gardner and Prof. Converse, who are already monitoring seabirds in Tetiaroa. This research project will also be a key opportunity to address fundamental questions in evolutionary ecology, for example by studying morphological and behavioral changes in lizards and crabs following rat removal. To carry out this project, we would therefore like to have access to all 12 motus of Tetiaroa, in order to follow sites with different histories of occupation by Polynesian and black rats, and different communities of nesting seabirds, while taking advantage of the existence of similar sites replicating the same types of conditions across the atoll. Although this is a long-term project, in the short term, our priority is to accumulate a maximum of information on the ecosystems before the removal of the rats, especially with regards to direct effects of rats (e.g., predation) on the local fauna. We are thus hoping to come to Tetiaroa for about 4 weeks before the eradication. Our ideal dates would thus be from the 5th of July to the 2nd of August.

Visit #72068 @Tetiaroa Society Ecostation

Approved

Under Project # 46745 | Research

Effects of rat eradication on the terrestrial ecosystems of Tetiaroa

faculty - Institut de recherche pour le développement

Reservation Members(s)

Simon Ducatez Jul 5 - Aug 2, 2021 (29 days)
Jayna DeVore Jul 5 - Aug 2, 2021 (29 days)

Reserve Resources(s) | Create Invoice

Ecostation Rate 2 Jul 5 - Aug 2, 2021