Invasive rat drives complete collapse of native small mammal communities in insular forest fragments

A survey of VKORC1 missense mutations in eleven Italian islands reveals widespread rodenticide resistance in house mice

To protect native wildlife, more than one hundred rodent eradications have been attempted in the Mediterranean islands by using anticoagulant rodenticides (ARs). Despite their high efficiency, resistance to ARs has been observed in many countries and it is mostly related to missense mutations (SNPs) in the VKORC1 gene. The presence of resistant individuals reduces the efficiency of rodent management, leading to an excessive use of ARs. Thus, the risk of poisoning in non-target species increases. In this study, the first survey of ARs resistance in the house mouse Mus domesticus covering multiple islands in the Mediterranean was performed. Tissue samples of eighty-two mice from eleven islands in Italy were analysed and eight missense SNPs were found. In addition to some well-known missense mutations, such as Tyr139Cys, six new missense SNPs for the house mouse were discovered, four of which were new even for any rodent species. Furthermore, the frequency of Tyr139Cys significantly increased in Ventotene Island after a four-year long rat eradication. This could be due to the selective pressure of ARs that allowed the mice carrying the mutation to survive. This study demonstrates once again the importance of assessing resistance to ARs before undertaking rodent eradications. Indeed, this would allow an informed decision of the most effective AR to use, maximizing the success rate of the eradications and minimizing secondary poisoning and other deleterious effects for non-target species and the environment.

Widespread distribution of rodenticide resistance-conferring mutations in the Vkorc1 gene among house mouse populations in Portuguese Macaronesian islands and Iberian Atlantic areas

Growing evidence of widespread resistance to anticoagulant rodenticides (ARs) in house mice pose significant challenges to pest control efforts. First-generation ARs were introduced in the early 1950s but resistance to these emerged later that decade. Second-generation rodenticides were then developed, with resistance being reported in the late 1970s. Research has linked resistance to ARs with mutations in the Vkorc1 gene, leading to the use of more toxic and environmentally harmful compounds. In this study, 243 tail tips of house mice from mainland Portugal and Southern Spain, the Azores and Madeira archipelagos were analysed for all 3 exons of the Vkorc1 gene. Mutations L128S, Y139C, along with the so-called spretus genotype Vkorc1spr are considered responsible for reduced susceptibility of house mice to ARs. All these sequence variants were broadly detected throughout the sampling regions. Vkorc1spr was the most often recorded among mainland populations, whereas Y139C was nearly ubiquitous among the insular populations. In contrast, L128S was only detected in mainland Portugal and four islands of the Azores archipelago. All first generation ARs such as warfarin and coumatetralyl are deemed ineffective against all Vkorc1 variants identified in this study. Second-generation bromadiolone and difenacoum should also be discarded to control populations carrying Vkorc1spr, Y139C or L128S mutations. Inadequate use of ARs in regions where resistant animals have been found in large proportions will result in the spreading of rodenticide resistance among rodent populations through the positive selection of non-susceptible individuals. Consequently, ineffectiveness of rodent control will increase and potentiate environmental contamination, hazarding non-target wildlife through secondary poisoning. We highlight the need for Vkorc1 screening as a crucial tool in rodent management, aiding in the selection of the most appropriate control/eradication method in order to prevent misuse of these toxic biocides and the spread of rodenticide resistance among house mouse populations.

The rise of hyperabundant native generalists threatens both humans and nature

In many disturbed terrestrial landscapes, a subset of native generalist vertebrates thrives. The population trends of these disturbance-tolerant species may be driven by multiple factors, including habitat preferences, foraging opportunities (including crop raiding or human refuse), lower mortality when their predators are persecuted (the 'human shield' effect) and reduced competition due to declines of disturbance-sensitive species. A pronounced elevation in the abundance of disturbance-tolerant wildlife can drive numerous cascading impacts on food webs, biodiversity, vegetation structure and people in coupled human-natural systems. There is also concern for increased risk of zoonotic disease transfer to humans and domestic animals from wildlife species with high pathogen loads as their abundance and proximity to humans increases. Here we use field data from 58 landscapes to document a supra-regional phenomenon of the hyperabundance and community dominance of Southeast Asian wild pigs and macaques. These two groups were chosen as prime candidates capable of reaching hyperabundance as they are edge adapted, with gregarious social structure, omnivorous diets, rapid reproduction and high tolerance to human proximity. Compared to intact interior forests, population densities in degraded forests were 148% and 87% higher for wild boar and macaques, respectively. In landscapes with >60% oil palm coverage, wild boar and pig-tailed macaque estimated abundances were 337% and 447% higher than landscapes with <1% oil palm coverage, respectively, suggesting marked demographic benefits accrued by crop raiding on calorie-rich food subsidies. There was extreme community dominance in forest landscapes with >20% oil palm cover where two pig and two macaque species accounted for >80% of independent camera trap detections, leaving <20% for the other 85 mammal species >1 kg considered. Establishing the population trends of pigs and macaques is imperative since they are linked to cascading impacts on the fauna and flora of local forest ecosystems, disease and human health, and economics (i.e., crop losses). The severity of potential negative cascading effects may motivate control efforts to achieve ecosystem integrity, human health and conservation objectives. Our review concludes that the rise of native generalists can be mediated by specific types of degradation, which influences the ecology and conservation of natural areas, creating both positive and detrimental impacts on intact ecosystems and human society.

Terrestrial food web complexity in Amazonian forests decays with habitat loss

The conversion of natural ecosystems into human-modified landscapes (HMLs) is the main driver of biodiversity loss in terrestrial ecosystems.^1,2,3 Even when species persist within habitat remnants, populations may become so small that ecological interactions are functionally lost, disrupting local interaction networks.^4,5 To uncover the consequences of land use changes toward ecosystem functioning, we need to understand how changes in species richness and abundance in HMLs^6,7,8 rearrange ecological networks. We used data from forest vertebrate surveys and combined modeling and network analysis to investigate how the structure of predator-prey networks was affected by habitat insularization induced by a hydroelectric reservoir in the Brazilian Amazonia.⁹ We found that network complexity, measured by interaction diversity, decayed non-linearly with decreasingly smaller forest area. Although on large forest islands (>100 ha) prey species were linked to 3-4 potential predators, they were linked to one or had no remaining predator on small islands. Using extinction simulations, we show that the variation in network structure cannot be explained by abundance-related extinction risk or prey availability. Our findings show that habitat loss may result in an abrupt disruption of terrestrial predator-prey networks, generating low-complexity ecosystems that may not retain functionality. Release from predation on some small islands may produce cascading effects over plants that accelerate forest degradation, whereas predator spillover on others may result in overexploited prey populations. Our analyses highlight that in addition to maintaining diversity, protecting large continuous forests is required for the persistence of interaction networks and related ecosystem functions.