Anthropogenic subsidies mitigate environmental variability for insular rodents

Area of Science:

• Island ecology
• Invasive species dynamics
• Population biology

Background:

• Island ecosystems are sensitive to nutrient and energy inputs.
• Anthropogenic resource subsidies can disproportionately benefit non-native consumers.
• Introduced black rats (Rattus rattus) are significant components of island food webs.

Purpose of the Study:

• To test if super-abundant gulls and invasive iceplants alter black rat population dynamics.
• To investigate the effects of anthropogenic subsidies on rat density, age-ratio, and growth rates.
• To determine how rainfall variability modulates the impact of subsidies on rat populations.

Main Methods:

• Field study on Bagaud Island comparing three habitats: gull colony, iceplant-dominated, and native scrubland.
• Rat trapping conducted over two years with contrasting rainfall patterns.
• Analysis of rat density, age-structure, and growth rates in relation to habitat and environmental conditions.

Main Results:

• Rat growth rates in native scrubland varied with environmental fluctuations, unlike in the gull colony where growth remained high.
• Anthropogenic subsidies, particularly from gulls, mitigated environmental stress for rats.
• Rat density and age structure varied significantly across habitats, seasons, and years, with higher densities in gull colonies.

Conclusions:

• Anthropogenic subsidies provide a critical resource base for invasive species like black rats on islands.
• Resource subsidies can buffer invasive populations from environmental variability, potentially increasing their impact.
• Understanding these dynamics is crucial for managing invasive species on islands worldwide.