Exotic black rats increase invertebrate Ordinal richness in urban habitat remnants

• Published in: Biological invasions 2017-04, Vol.19 (4), p.1315-1328
• Main Authors: Smith, Helen M., Dickman, Chris R., Banks, Peter B.
• Format: Article
• Language: English
• Subjects: Araneae; Biodiversity; Developmental Biology; Ecology; Freshwater & Marine Ecology; Invertebrata; Invertebrates; Life Sciences; Original Paper; Plant Sciences; Predation; Predators; Rats; Rattus rattus; Rodents; Spiders; Trophic levels; Urban areas; Wildlife
• ISSN: 1387-3547; 1573-1464
• DOI: 10.1007/s10530-016-1340-x

Exotic predators have had devastating impacts on native wildlife globally and have stimulated many attempts to control or eradicate them. However, removing an exotic predator is predicted to have wider consequences if the exotic predator plays an apex role in its new community, including negative impacts on other community members via disruption to trophic or ecological cascading processes. Here, we examine the potential role of the commensal black rat ( Rattus rattus ) as an exotic higher-order predator in urban habitat remnants in Sydney, Australia. Given that black rats are generalist predators on invertebrates that occupy many trophic levels, we applied trophic cascade theory and predicted that there would be an inverse relationship between the numbers of black rats and smaller invertebrate predators, especially spiders, and a positive relationship between black rats and the numbers, richness and diversity of lower-order invertebrates that are preyed upon by spiders. Using a controlled and replicated removal experiment spanning 10 months of rat-removal and 6–12 weeks of invertebrate sampling, we found both more spiders on black rat-removal sites and lower invertebrate Ordinal richness. Our results thus support our hypotheses and suggest that this exotic rodent may suppress spiders but have an overall positive influence on other invertebrates, perhaps by ‘releasing’ them from spider predation. Although further experimental studies are needed to test the generality of our findings and to critically identify the causal processes involved, we conclude that—at least in certain circumstances—an exotic predator can have potentially positive effects on components of its new ecosystem.