Microclimate is a strong predictor of the native and invasive plant-associated soil microbiome on San Cristóbal Island,Galápagos archipelago

Understanding the drivers that affect soil bacterial and fungal communities is essential to understanding and mitigating the impacts of human activity on vulnerable ecosystems like those on the Galápagos Islands. The volcanic slopes of these Islands lead to steep elevation gradients that generate distinct microclimates across small spatial scales. Although much is known about the impacts of invasive plant species on the above-ground biodiversity of the Galápagos Islands, little is known about their resident soil microbial communities and the factors shaping them. Here, we investigate the bacterial and fungal soil communities associated with invasive and native plant species across three distinct microclimates on San Cristóbal Island (arid, transition zone and humid). At each site, we collected soil at three depths (rhizosphere, 5 cm and 15 cm) from multiple plants. Sampling location was the strongest driver of both bacterial and fungal communities, explaining 73% and 43% of variation in the bacterial and fungal community structure, respectively, with additional minor but significant impacts from soil depth and plant type (invasive vs. native). This study highlights the continued need to explore microbial communities across diverse environments and demonstrates how both abiotic and biotic factors impact soil microbial communities in the Galápagos archipelago.     

Response of mice (Mus musculus) to the removal of black rats (Rattus rattus) in arid forest on Santa Cruz Island, Galápagos

A combined rat and mouse trapping grid was established in arid coastal forest on Santa Cruz Island, Galápagos over June and July 2009. Mouse traps were opened first and did not initially catch any mice. Rat traps were opened four days later and began catching rats on the second night. Mice were trapped in increasing numbers only after the rat catch-rate had declined substantially. Interference with bait at rat traps also increased. The estimated density of rats was 4.8 rats/ha and mice 32.3/ha. The results suggest mice were present but their activity and/or numbers were being suppressed by the larger rodent. This conclusion has implications for competitive exclusion of native Galápagos rodents by both introduced species. It also suggests caution for rodent abundance estimates and planned rodent eradications when two or more species are present.