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# Stable isotope analysis as an early monitoring tool for community-scale effects of rat eradication: Rat eradication affects crab trophic ecology

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... (illustrations by Devyn Orr; vector images by Tracey Saxby and Sally Bell, Integration and Application Network, University of Maryland Center for Environmental Science (ian.umces.edu/imagelibrary/) (this includes the largest terrestrial arthropod, the coconut crab Birgus latro) (Nigro et al., 2017). Additionally, depending on whether black rats preferentially target C. nucifera seeds or the seeds of other introduced or native species, plant community composition may shift in favor of the introduced C. nucifera or in favor of native species. ...
... nucifera) responded at greater magnitudes (2-5 times) than other tree species to seed predation release, even though all these tree species were heavily targeted by rodent seed predators and have seen some population recovery following eradication (Wegmann, 2009;Wolf et al., 2018). The differential responses of plant species to rat eradication may be due to rat food preference, inability to effectively kill seeds of a species (thus providing a benefit as a seed disperser), the reproductive ability of the tree, the tree's ability to escape predation by other seed predators when rats are not in the system, or a combination of these or other factors (Clark, 1981;Hayes & Barry, 2008;Nigro et al., 2017;Young, Mccauley, Guevara, et al., 2013). In this system, it is likely that the differential advantage of C. nucifera comes from the natural history of the tree, since evidence from rat husking stations on Palmyra Atoll suggest that rats predate seeds of most of the canopy trees in this system and cause seed mortality in the majority of predation events for all seed species, thus providing little or no benefit as a seed disperser for this or other tree species (Wegmann, 2009). ...
... Although we saw some evidence that the coconut crab (Birgus latro), the only native seed predator effective at predating C. nucifera seeds once they reach the ground, is predating some seeds in the absence of rats, the relative rarity of this predation compared to rat predation suggests that coconut crabs will not compensate for rats in the short term. However, the increased frequency with which coconut crabs are now observed in C. nucifera forests following black rat eradication suggests this is a process that warrants longer-term monitoring (Nigro et al., 2017). B. latro and other terrestrial crabs in this system (hermit crabs: Coenobita brevimanus and Coenobita perlatus and land crabs: Cardisoma carnifex and Cardisoma rotundum) preferentially predate seeds of rare tree species, so the disproportionate immediate benefit to C. nucifera may only be exacerbated by seed selection of native seed predators for seeds of rarer canopy trees (Nigro et al., 2017;Young, Mccauley, Dunbar, et al., ). ...
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... Partly due to this conspicuous behaviour, they are among the most well-studied decapods, and many aspects of their biology and life-history have been thoroughly described, including shell utilization (Abrams, 1978), locomotion (Herreid and Full, 1986;Osorno et al., 1998), olfaction (Small and Thacker, 1994; Szabo, 2012), water balance (Gross, 1964), ontogeny (Brodie, 1999;Hamasaki et al., 2015;Taylor, 1988), moulting , feeding activities (Barnes, 1997a(Barnes, , 1997bPage and Willason, 1983), mating behaviour (Gusev and Zabotin, 2007), migration (Barnes, 1997a;Nieves-Rivera and Williams, 2003;Vannini, 1976), visual abilities (Ping et al., 2015), and respiration (McMahon and Burggren, 1979). In addition to their well-established biology and life-history, terrestrial hermit crabs are known to be susceptible to anthropogenic change (Chan et al., 2010; Nigro et al., 2017). Thus, earlier studies suggested that they might be suitable indicators for human-driven biodiversity changes (Brook et al., 2009;Cardoso et al., 2016). ...
... These drivers comprise habitat configuration, expressed as habitat niche occupation, and food web dynamics, expressed as trophic niche occupation (Soberón, 2007). By studying shifts or changes in habitat or trophic niche occupation following anthropogenic disturbance, it is possible to gain insights into the mechanisms that ultimately cause human-driven biodiversity loss (Nigro et al., 2017;Tilman, 1999). As already described in Chapter A, it is crucial to first establish niche occupation under the absence of anthropogenic disturbance as a baseline of a natural status quo before investigating possible humandriven changes in habitat or trophic niche occupation (de Graaf et al., 2004). ...
Thesis
Biodiversity on our planet follows defined patterns. On a global scale, these patterns are organized by few parameters, like latitude and elevation. On a local scale, the organization of biodiversity becomes less predictable as various factors simultaneously determine species’ diversity and distribution. Understanding how biodiversity and species distribution are organized on small spatial scales (i.e., within ecosystems or habitats) is fundamental to ecological research. This relevance stems from the ongoing global change. The increasing necessity for understanding how biodiversity and species distribution is organized exists because the most prevalent threat for biodiversity worldwide is land conversion, which acts primarily on a local scale (i.e., within ecosystems or habitats). Various land uses drive the conversion of former pristine ecosystems into modified and degraded land. A plethora of research has described the loss of habitat area or species richness following different human land uses. However, few studies reach beyond merely describing species losses and investigated the underlying mechanisms by which human activities alter the organization biodiversity and distribution. For a thorough understanding of how different human land uses impact the organization of biodiversity within ecosystems, it is first necessary understand how natural abiotic and biotic factors organize and drive biodiversity and distribution in natural systems free of any direct human disturbance before investigating any human-driven changes. Empirical research aiming to analyse the organization of biodiversity and distribution in ecosystems is often hindered by the overall ecosystem complexity and difficulty of demarcating and replicating communities or ecosystems. In this PhD thesis, I introduce a methodical framework that uses small insular ecosystems for investigating how biotic, abiotic, and anthropogenic factors drive biodiversity and distribution. The small sizes and clear boundaries of islands, together with the possibility to use groups of islands as ecosystem replicates, pose an elegant solution to the abovementioned limitations. This PhD thesis uses this insular framework as a model system to study how natural biotic and abiotic factors drive the organization of biodiversity and disentangle the impacts of different human land uses by investigating islands that hold only one specific type of human land use. For this, I consulted a two-step approach. In the first chapter of this PhD thesis, I used a focal taxon approach, while in the second chapter, I used a community-wide sampling approach. Analysing how abiotic, biotic, and anthropogenic factors drive biodiversity and distribution on two ecological levels enabled a more thorough understanding of the relevant factors, as both sampling approaches each bring their methodical advantages. In chapter A, I identified the key natural abiotic drivers for the distribution patterns of the investigated focal taxon, terrestrial hermit crabs (genus Coenobita), and show which physical conditions predominantly influence its distribution. At the same time, interspecific competition does not drive its biodiversity and distribution patterns. Instead, intrinsic mechanisms of resource partitioning stabilize co-occurrence. The investigation of the focal taxon’s biodiversity and distribution patterns on islands used either solely for touristic purposes (‘tourist islands’) or as permanent settlings by the local population (‘local islands’) disentangled the environmental impact of two different human land uses. I demonstrate that two forms of human land use can impact different aspects of the same taxon in the same overall region. Single-taxon-approaches are limited in their generalizability and give less insight than community-wide analyses. Hence, chapter B focused on the ground-associated faunal community of the investigated insular ecosystem (section B.1-B.4 and B.5-B.6) and the avifauna (section B.4). I demonstrate that the biodiversity and distribution patterns of the ground-associated insular community are organized in a compartmentalized way, both concerning habitat niche occupation and trophic niche occupation. Closely related species cluster within the overall niche space and form compartments attributable to distinct insular habitats (e.g., a beach food web compartment and an inland food web compartment). I show that this compartmentalized organization is not occurring due to an overall depauperate insular fauna, but likely stabilized by relative productivity gradients between compartments. More mobile bird taxa likely also form no relevant link between the distinct compartments of the ground-associated infauna. I further show that both investigated forms of human land use have a negative impact on the insular biodiversity patterns. However, the drivers for the observed losses differ between the two land uses. Ultimately, I show that both land uses are related, at least partly, to significant shifts in the trophic niche occupation of the impacted species, which might indicate a species’ susceptibility to land-use-driven abundance declines. By using islands as the methodical framework to study how biodiversity and species distribution is organized on a local scale and how human land uses alter these patterns, this PhD thesis paves the way for future research in community and disturbance ecology. The novelty of this insular approach is further emphasized by the presentation of two species newly recorded in the investigated insular region in the final chapter of my thesis. This underlines the broad spectrum of possible scientific insights that islands as model systems offer for biodiversity research.
... An alternative means for assessing ecosystem recovery to species level monitoring is to examine indicators of ecosystem functioning. Ecosystem functioning processes such as changing nutrient dynamics provide insight on a range of species and their interactions (Nigro et al., 2017). ...
... Several studies have compared seabird-derived nutrients in ecosystem components such as soil, plants and invertebrates on islands with and without invasive species, for example islands with and without foxes in the Aleutian Archipelago (Croll et al., 2005) and islands with and without rats in New Zealand (Fukami et al., 2006;Jones, 2010aJones, , 2010b, on islets around Palmyra Atoll in the Pacific (Nigro et al., 2017), islands off Mexico (Samaniego-Herrera et al., 2017) and in the Chagos Archipelago in the Indian Ocean (Graham et al., 2018). In all apart from the Mexican study system, seabird-derived nitrogen levels (as measured by enriched nitrogen isotope levels) in the assessed ecosystem components were higher on islands without invasive species than those with invasive species. ...
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Abstract Monitoring seabird‐derived nutrients on islands following invasive mammal eradications may provide a useful, cost‐ and time‐efficient indication of the recovery of ecosystem function; however, the technique has only been investigated on environmentally similar islands. How seabird‐derived nutrients recover on islands with different characteristics, and how differences in sampling regimes affect results is poorly understood. To determine how different island characteristics (size, geographic location and invasion history) and aspects of the sampling regime (sample collection year, season and intra‐island location) influence seabird‐derived nutrients we collated nitrogen stable isotope (δ15N) data from three ecosystem components (soil, plants and spiders), collected on 28 islands around New Zealand. We investigated which variables best predict δ15N using linear‐mixed effects models. Accounting for these variables and using still‐invaded and never‐invaded islands as controls for recovery, we then investigated changes in δ15N on islands at different stages following invasive mammal eradication. Island size, invasion history and the presence of seabirds in the direct vicinity of a sampling location all influenced δ15N. After accounting for these variables, δ15N increased with time since eradication in soils, plants and spiders, though there was still some variation that our chosen variables could not explain. This study demonstrates the importance of considering island characteristics and sampling methods when assessing seabird‐derived nutrient recovery and highlights the need for additional targeted sample collection on islands to help separate out the effects of time since eradication and other confounding variables affecting δ15N. Improved understanding of these factors will be prerequisite for furthering this technique as a useful addition to the post‐eradication monitoring tool kit.
... A principal component analysis (PCA) of the shell morphometrics was then applied to compare the decisive criteria of the shell morphology between the co-occurring species. As research organisms to test competition theory, the only terrestrial hermit crab genus, Coenobita, was chosen, because it has already been established that the two co-occurring hermit crab species in the investigated system, C. rugosus and C. perlatus, are both primarily beach associated and unspecialized detritus feeders with no clear food preferences [31][32][33]. They are therefore an ideal system to test for the effect of the shell resource on coexistence, because other potentially limiting factors can be excluded upfront. ...
... Partitioning of or competition over the food resource can also be excluded as a driver for coexistence, as previous studies demonstrated that C. rugosus and C. perlatus are both unspecific detritus feeders with no clear food preference [32,43] and not limited by food availability [10,14,22]. ...
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Background: Coexistence is enabled by ecological differentiation of the co-occurring species. One possible mechanism thereby is resource partitioning, where each species utilizes a distinct subset of the most limited resource. This resource partitioning is difficult to investigate using empirical research in nature, as only few species are primarily limited by solely one resource, rather than a combination of multiple factors. One exception are the shell-dwelling hermit crabs, which are known to be limited under natural conditions and in suitable habitats primarily by the availability of gastropod shells. In the present study, we used two co-occurring terrestrial hermit crab species, Coenobita rugosus and C. perlatus, to investigate how resource partitioning is realized in nature and whether it could be a driver of coexistence. Results: Field sampling of eleven separated hermit crab populations showed that the two co-occurring hermit crab species inhabit the same beach habitat but utilize a distinct subset of the shell resource. Preference experiments and principal component analysis of the shell morphometric data thereby revealed that the observed utilization patterns arise out of different intrinsic preferences towards two distinct shell shapes. While C. rugosus displayed a preference towards a short and globose shell morphology, C. perlatus showed preferences towards an elongated shell morphology with narrow aperture. Conclusion: The two terrestrial hermit crab species occur in the same habitat but have evolved different preferences towards distinct subsets of the limiting shell resource. Resource partitioning might therefore be the main driver of their ecological differentiation, which ultimately allowed these co-occurring species to coexist in their environment. As the preferred shell morphology of C. rugosus maximizes reproductive output at the expense of protection, while the preferred shell morphology of C. perlatus maximizes protection against predation at the expense of reproductive output, shell resource partitioning might reflect different strategies to respond to the same set of selective pressures occurring in beach habitats. This work offers empirical support for the competitive exclusion principle-hypothesis and demonstrates that hermit crabs are an ideal model organism to investigate resource partitioning in natural populations.
... Of the habitat types included, all were from the marine ecosystems. None of the terrestrial habitats met our criteria, due to lack of reference data or only including a single species (Kupilas et al. 2016, Nigro et al. 2017). ...
... Many restoration studies conduct a before and after restoration or a restored vs degraded/impacted approach (e.g. Kupilas et al., 2016;Nigro et al., 2017), but neither approach lends itself to the hypervolume approach to understand recovery because the lack of a reference site to compare. In specific systems, finding a reference site to compare may be extremely difficult, limiting the usefulness of using hypervolume analysis to manage these systems. ...
Article
The primary goal of habitat restoration is to recover the ecological structure, function, and services of natural ecosystems lost due to disturbance. Post-restoration success typically focuses on the return of a desired habitat type, consumer species composition, or abundance relative to a reference site. However, how energy flow responds to habitat restoration has not been widely studied, and there is a need to develop a better understanding of how energy flows through a restored vs reference ecosystem following restoration. We tested recently developed niche metrics as a tool to assess the degree of recovery of ecosystem energy flow and evaluate the success of habitat restoration. Using published stable isotope values from six systems, one to three years post-restoration, we used Bayesian mixing models to quantify resource use by consumers to generate food web hypervolumes for restored and reference habitats in each ecosystem and to quantify similarity in resource use between restored and reference systems. Our analysis showed that there were differences in restoration success at each restoration project between the restored and reference food webs, but two general patterns emerged in the early stages following restoration. Restoration efforts that restore biogenic habitats display lower levels of recovery of food web function than those that only restore abiotic habitat structural. Restoration increases the variability in basal resource use of consumers in food webs that rely heavily on one basal resource, while in food webs that relied on multiple basal resources consumers decrease variability in basal resource use. Our results demonstrate that hypervolume analysis is a powerful tool that can be used to quantify energy flow, the recovery of food web function, and measure restoration success.
... Carbon and nitrogen stable isotope compositions (δ 13 C and δ 15 N) of biota may be an alternative means to detect early environmental changes in aquatic ecosystems (Oczkowski et al. 2014;Wang et al. 2015;Gooddy et al. 2016;Nigro et al. 2017) and can provide insight into the sources, sinks, and cycling of carbon and nitrogen in biota that interact with their physical and chemical environments. Several studies have indicated that δ 13 C and δ 15 N values can be used as early indicators for environmental changes (McKee et al. 2002;Wang et al. 2015;Zhang et al. 2016;Nigro et al. 2017). ...
... Carbon and nitrogen stable isotope compositions (δ 13 C and δ 15 N) of biota may be an alternative means to detect early environmental changes in aquatic ecosystems (Oczkowski et al. 2014;Wang et al. 2015;Gooddy et al. 2016;Nigro et al. 2017) and can provide insight into the sources, sinks, and cycling of carbon and nitrogen in biota that interact with their physical and chemical environments. Several studies have indicated that δ 13 C and δ 15 N values can be used as early indicators for environmental changes (McKee et al. 2002;Wang et al. 2015;Zhang et al. 2016;Nigro et al. 2017). The 13 C depletion in the mangrove trees has been attributed to reduced stomatal conductance under environmental stressors such as nutrients and salinity (Lin and Sternberg 1992;McKee et al. 2002). ...
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Abstract Background Florida’s Everglades is a vast freshwater peatland that has been impacted by the alterations of hydrological pattern and water quality which led to changes in plant species composition and biodiversity. In this study, carbon and nitrogen stable isotopes (δ13C and δ15N) in cattail (Typha domingensis) are evaluated as indicators of environmental changes in the Everglades wetlands along nutrient and hydrological gradients represented by reference sites with total phosphorus (TP) < 10 μg L−1, transition sites with TP ≥ 10 μg L−1 < 20 μg L−1 and impacted sites with TP ≥ 20 μg L−1 which differed in hydrology or habitats (marsh and canal). Results Cattail δ13C values decreased significantly from reference (–24.1‰), transition (–26.8‰) to the impacted sites (–28.2‰). In contrast, δ15N values increased significantly from reference (–5.2‰), transition (2.4‰) to the impacted site (5.9‰). In response to a poor hydrological condition, cattail in marsh area displayed 13C enrichment (–26.0‰) and 15N depletion (0.2‰). By contrast, cattail grown in the canal sites with favorable hydropattern displayed 13C depletion (–27.6‰) and 15N enrichment (5.9‰) from the canal sites with more favorable hydrological condition. Conclusions The different patterns for the changes in δ13C and δ15N in cattail suggested that increased nutrients led to increased stomatal conductance and 13C fractionation during carbon uptake and decreased 15N fractionation with increasing nitrogen demand while poor hydrological condition coupled with low nutrients led to reduced plant growth indicated by higher δ13C and lower δ15N values. Findings from this study suggested that δ13C in emerged macrophytes such as cattail can be used as an indicator for environmental stress while δ15N is a robust indicator for wetland eutrophication.
... Kemp (2019), for instance, found a 78% of reduction in bat diet trophic niche with 26% of tropical forest decline on Borneo and explained it by a reduced diversity of basal resources and insect prey available to bats in degraded forests. An opposite effect was achieved by management efforts aiming to diminish human impact: invasive rat (Rattus rattus) eradication on Palmyra Atoll was followed by a pronounced expansion of the isotopic niche of the native land crab (Geograpsus spp.) community due to release of several crab species from predation and competition with rats (Nigro et al., 2017). ...
Article
Linking their major biotic and abiotic components, food webs form the core of ecosystems, many of which are today exposed to multiple human impacts acting at several spatial and temporal scales. A food web perspective allows for a quantification of environmental change effects on both the structure of biological diversity and the functioning of ecosystems. Food web metrics based on stable isotope analysis (SIA) represent a promising way for an integrative assessment of these responses. While showing high sensitivity to environmental change, they are, however, rarely presented and discussed within a systematic mechanistic and hypothesis-driven framework. Here we first provide a global overview of anthropogenic impact types, their effects on food webs and the associated ecological mechanisms. Based on published studies from terrestrial, freshwater and marine ecosystems, we then demonstrate the versatility of SIA-based metrics, allowing for quantification of several key food web attributes and applicable across a wide range of human-induced impacts such as eutrophication, pollution, introduction of exotic species or connectivity interruption. We finally propose a guiding framework to make SIA application in the studies of anthropogenic impact on food webs more rigorous and enhance its potential for producing novel insights.
... In New Zealand, two endemic bats (Mystacina robusta and M. tuberculata) have gone extinct due to black rats (Daniel, 1990). Furthermore, rats predations is highly related to the decline or extinction of the green sea turtle (Caut et al., 2008), various lizards and amphibians (Clark, 1981), and terrestrial crustaceans (Page & Meier, 2006;Nigro et al., 2017). ...
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The Bonin Islands are oceanic islands of Japan that have never been connected to the continent, and include abundant endemic species and ecosystems. These islands were registered as a UNESCO Natural World Heritage Site in 2011, along with other islands of the Ogasawaras. The environment of the Bonin Islands has been disturbed by development and livestock since human settlement began, and many native organisms remain at risk of extinction due to alien species introduced by humans. To conserve and restore the native ecosystems, alien animals (cats, goats, pigs, bullfrogs, and rodents) have been eradicated on several islands through alien species control projects conducted with the cooperation of administrative organs, the private sector, and residents. The outcomes of these projects highlight the importance of understanding the interactions among multiple alien species and considering the indirect effects of alien species control. However, in recent years, further alien species countermeasures have been required for the big-headed ant and land nemerteans, which have been identified as posing an ecological risk, and for a predatory snail that has recently invaded. Control strategies for alien animals are associated with many issues, including legal restrictions, environmental and human impacts, and technical aspects. In particular, it is difficult to eradicate small-sized species that have high fecundity and invade easily. Therefore, for future protection of the Bonin Islands as a Natural World Heritage Site, it is essential to strengthen the quarantine system to prevent alien species from dispersing on other islands, and to prevent new alien species from invading. Full text: http://www.airies.or.jp/journal_GlobalEnvironmentalResearch_202004020943372.html
... Combining multiple methodological approaches to examine the diet of this invasive species has allowed us to robustly estimate these effects. Stable isotopes have been proposed as a tool to rapidly detect ecosystem recovery following invasive rodent eradication (Nigro et al. 2017). However, due to the limited and isotopically similar prey base on Antipodes Island, this method would struggle to capture changes in native consumers if used in isolation. ...
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House mice (Mus musculus) are a widespread invasive species on islands. Where they are the sole introduced mammal they can have particularly strong negative impacts on recipient ecosystems. House mice impacts have been documented on almost every component of the terrestrial ecosystem on Southern Ocean islands, including plants, invertebrates, birds and ecosystem function. We undertook a comprehensive study to determine the impacts of house mice on Antipodes Island, New Zealand. This study was done prior to mouse eradication to inform monitoring and restoration. We used invertebrate pitfall trapping on the main Antipodes Island and neighbouring mouse-free offshore islands together with mouse stomach contents and stable isotope analyses of mouse livers to examine dietary preferences. We identified directly impacted and consumed invertebrate Orders relative to their abundance and provided a comprehensive picture of resource flow and overlap in the invaded terrestrial ecosystem. The remote terrestrial ecosystem of Antipodes Island was tightly circumscribed with strong resource overlap. Mouse diet varied seasonally with resource availability, dominated by invertebrates and land birds in summer, and plants and seabirds in winter. Invertebrates that were preferentially preyed upon were Amphipoda, Lepidoptera and some species of Coleoptera. These patterns suggest the ecosystem is annually driven by a seasonal bottom-up resource pulse over summer, where mice are a selective predator, differentially preying on invertebrates relative to invertebrate abundance. Mice appear to be exhausting preferred prey as they systematically consume their way through the terrestrial ecosystem. Land bird diet also varied seasonally and some of these birds likely competed with mice for invertebrate prey. Eradication of mice from Antipodes Island should reduce the predation on invertebrates and reduce the effects of competition and predation on land birds. This should have flow-on effects to the abundance of invertebrates and endemic land bird sub-species of pipit and snipe.
... Stable isotope analysis (SIA) is one of the primary tools used to examine the structure and dynamics of food webs 22 and may represent a unifying methodology with which to compare anthropogenic pressures among different coastal ecosystems 23 . SIA provide time-and space-integrated information on the trophic interactions of species 18 in disturbed, undisturbed or restored ecosystems 24 . An example of SIA applicability is the assessment of the effects of invasive species on the trophic structure of native communities. ...
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As a result of the increased urban and agricultural development in coastal environments, estuaries are among the most modified and threatened aquatic ecosystems. This study used stable isotopes to examine the effects of human impacts by contrasting the food web structures of two Iberian estuaries exposed to different degrees of human pressure. More complex feeding pathways were found in the more altered estuary (Guadalquivir). Greater spread among species along the carbon axis suggests that the primary consumers exploit organic matter with various origins, whereas different nitrogen signals of the secondary consumers suggest that they feed on different suites of prey. In contrast, the similar isotopic signals of secondary consumers in the relatively little influenced estuary (Guadiana) suggests similarity in diet composition and feeding on the same organic matter sources. Understanding trophic interactions in estuaries is vital for defining proper management and conservation, and the preliminary data provided here are one step in this direction.
... 4. Land crabs are significant seed predators and herbivores that are known to affect plant community structure on remote oceanic islands [59,60]. On Palmyra Atoll, rats were known to limit crab numbers [33], and five years post-eradication the relative abundance of several crab species appears to be increasing [61], potentially leading to increased consumption of seeds and seedlings by land crabs. The impacts of crabs on seedling recruitment may continue to increase as their populations grow following release from invasive rat predation. ...
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... In June 2011, the approximately 40 000 rats on Palmyra were eradicated by applying brodifacoum [9]. After rat eradication, rat prey, like palm seedlings and crabs, increased [10]. Although mosquitoes still harassed people in the evenings, visitors found it unnecessary to apply mosquito repellent during the day and began to suspect Aedes had been extirpated. ...
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The Asian tiger mosquito,Aedes albopictus,appears to have been extirpated from Palmyra Atoll following rat eradication. Anecdotal biting reports, collection records, and regular captures in black-light traps showed the species was present before rat eradication. Since then, there have been no biting reports and no captures over 2 years of extensive trapping (black-light and scent traps). By contrast, the southern house mosquito,Culex quinquefasciatus,was abundant before and after rat eradication. We hypothesize that mammals were a substantial and preferred blood meal forAedes, whereasCulexfeeds mostly on seabirds. Therefore, after rat eradication, humans and seabirds alone could not support positive population growth or maintenance ofAedesThis seems to be the first documented accidental secondary extinction of a mosquito. Furthermore, it suggests that preferred host abundance can limit mosquito populations, opening new directions for controlling important disease vectors that depend on introduced species like rats.
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Eleven years after invasive Norway rats ( Rattus norvegicus ) were eradicated from Hawadax Island, in the Aleutian Islands, Alaska, the predicted three-level trophic cascade in the rocky intertidal, with native shorebirds as the apex predator, returned, leading to a community resembling those on rat-free islands with significant decreases in invertebrate species abundances and increases in fleshy algal cover. Rats had indirectly structured the intertidal community via their role as the apex predator in a four-level trophic cascade. Our results are an excellent example of an achievable and relatively short-term community-level recovery following removal of invasive animals. These conservation successes are especially important for islands as their disproportionately high levels of native biodiversity are excessively threatened by invasive mammals.
Article
The introduction of non-native rats can devastate island ecosystems. It now emerges that these rats also harm a complex web of interactions linking seabirds with the algae and fishes of nearby coral reefs. The introduction of non-native rats can devastate island ecosystems. It now emerges that these rats also harm a complex web of interactions linking seabirds with the algae and fishes of nearby coral reefs.
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More than US$21 billion is spent annually on biodiversity conservation. Despite their importance for preventing or slowing extinctions and preserving biodiversity, conservation interventions are rarely assessed systematically for their global impact. Islands house a disproportionately higher amount of biodiversity compared with mainlands, much of which is highly threatened with extinction. Indeed, island species make up nearly two-thirds of recent extinctions. Islands therefore are critical targets of conservation. We used an extensive literature and database review paired with expert interviews to estimate the global benefits of an increasingly used conservation action to stem biodiversity loss: eradication of invasive mammals on islands. We found 236 native terrestrial insular faunal species (596 populations) that benefitted through positive demographic and/or distributional responses from 251 eradications of invasive mammals on 181 islands. Seven native species (eight populations) were negatively impacted by invasive mammal eradication. Four threatened species had their International Union for the Conservation of Nature (IUCN) Red List extinction-risk categories reduced as a direct result of invasive mammal eradication, and no species moved to a higher extinction-risk category. We predict that 107 highly threatened birds, mammals, and reptiles on the IUCN Red List—6% of all these highly threatened species—likely have benefitted from invasive mammal eradications on islands. Because monitoring of eradication outcomes is sporadic and limited, the impacts of global eradications are likely greater than we report here. Our results highlight the importance of invasive mammal eradication on islands for protecting the world’s most imperiled fauna. Article Full-text available Birgus latro has significant conservation and socio-economic importance throughout its range, yet very little is known about its growth in its natural habitat. An extensive mark-recapture program was undertaken on Christmas Island, Australia, in which over 1440 individual crabs were uniquely identified using passive integrated transponder (PIT) tags. Over 18% of the tagged population was recaptured at least once and remeasured, providing substantial information on growth of B. latro. Our results show that in its natural setting B. latro is a very slow-growing species. Individuals commonly experience conditions that result in zero or negative growth. Sex, size, and injury all strongly influence the crab's moult increment. Males approached zero growth at around 65 mm in thoracic length (TL), while growth in females started to plateau at around 50 mm TL. Injury frequently led to negative growth, particularly in individuals that had lost a claw and/or multiple limbs-presumably due to a loss of foraging opportunities or access to other resources and a redistribution of available energy into limb regrowth. Our study indicates that previous growth curves do not adequately describe the growth of B. latro in its natural setting and that individual crabs may live over 30 yr longer than previously predicted, with large crabs likely to be over 100 years old. This may have serious implications for the long-term conservation of the species in the face of continuing exploitation. Article Full-text available Article Full-text available The three most invasive rat species, black or ship rat Rattus rattus, brown or Norway rats, R. norvegicus and Pacific rat, R. exulans have been incrementally introduced to islands as humans have explored the world’s oceans. They have caused serious deleterious effects through predation and competition, and extinction of many species on tropical islands, many of which are biodiversity hotspots. All three rat species are found in virtually all habitat types, including mangrove and arid shrub land. Black rats tend to dominate the literature but despite this the population biology of invasive rats, particularly Norway rats, is poorly researched on tropical islands. Pacific rats can often exceed population densities of well over 100 rats ha−1 and black rats can attain densities of 119 rats ha−1, which is much higher than recorded on most temperate islands. High densities are possibly due to high recruitment of young although the data to support this are limited. The generally aseasonally warm climate can lead to year-round breeding but can be restricted by either density-dependent effects interacting with resource constraints often due to aridity. Apparent adverse impacts on birds have been well recorded and almost all tropical seabirds and land birds can be affected by rats. On the Pacific islands, black rats have added to declines and extinctions of land birds caused initially by Pacific rats. Rats have likely caused unrecorded extinctions of native species on tropical islands. Further research required on invasive rats on tropical islands includes the drivers of population growth and carrying capacities that result in high densities and how these differ to temperate islands, habitat use of rats in tropical vegetation types and interactions with other tropical species, particularly the reptiles and invertebrates, including crustaceans. Article Full-text available Introduced species to oceanic islands can cause tremendous declines and extinctions of native avifauna. On Langara Island, British Columbia, Canada, the burrow-nesting ancient murrelet (Synthliboramphus antiquus) has declined from an estimated original population of 200,000 pairs to 14,600 pairs in 1993. Previously, causes of this decline were unknown, but the introduction of Norway rats (Rattus norvegicus) has been implicated as a major factor and has resulted in a recent rat eradication program. A major obstacle in the investigation of the effects of rats on seabirds, here and elsewhere, has been the inability to accurately assess the importance of seabirds to the diets of rats that also consume a variety of plants and invertebrates. We used stable-carbon (δ 13C), nitrogen (δ 15N), and sulphur$(\delta {}^{34}\text{S})$isotope analyses of muscle and liver tissues of rats and prey organisms from 3 regions of Langara Island to evaluate evidence for marine foods, including seabirds, in the diets of rats. Rats were segregated into 3 isotopic groups corresponding to upland, littoral, and seabird nesting areas on the island. We interpret these groups to represent individuals consuming predominantly C-3 terrestrial foods (x̄ δ 15N = 5.4‰; x̄ δ 13C = -24.9‰; n = 24), intertidal invertebrates (x̄ δ 15N = 8.9‰; x̄ δ 13C = -14.3‰; n = 21), and ancient murrelet adults, chicks, or eggs (x̄ δ 15N = 13.2‰; x̄ δ 13C = -17.6‰; n = 8). We found strong correlations between liver and muscle isotope values for both 13C and 15N, suggesting that dietary preferences within individuals remained relatively constant. Stable-sulphur isotope values of rat liver were less useful in segregating marine and terrestrial dietary inputs, possibly because sources of sulphur to the terrestrial food web were of marine origin (pooled x̄ δ 34S value = 17.8‰; n = 20). Our measurement of liver and muscle tissues gave dietary estimates based on relatively short- and long-term integrations and revealed the 3 groups of rats remained isotopically segregated at least over the 2-month period of ancient murrelet breeding on Langara Island. Our results have important ramifications for dietary investigations of introduced fauna and their effects on native seabirds on oceanic islands. Article Full-text available The black rat, roof rat, or ship rat (Rattus rattus L.) is among the most widespread invasive vertebrates on islands and continents, and it is nearly ubiquitous on Pacific islands from the equatorial tropics to approximately 55 degrees latitude north and south. It survives well in human-dominated environments, natural areas, and islands where humans are not present. Rattus rattus is typically the most common invasive rodent in insular forests. Few vertebrates are more problematic to island biota and human livelihoods than R. rattus; it is well known to damage crops and stored foods, kill native species, and serve as a vector for human diseases. Rattus rattus is an omnivore, yet fruit and seed generally dominate its diet, and prey items from the ground to the canopy are commonly at risk and exploited as a result of the prominent arboreal activity of R. rattus. Here we review the biology of this invasive species and its impacts on humans and the insular plants and animals in the Pacific. We also describe some of the past management practices used to control R. rattus populations on islands they have invaded. Article Full-text available New Zealand's offshore and outlying islands have long been a focus of conservation biology as sites of local endemism and as last refuges for many species. During the c. 730 years since New Zealand has been settled by people, mammalian predators have invaded many islands and caused local and global extinctions. New Zealand has led international efforts in island restoration. By the late 1980s, translocations of threatened birds to predator-free islands were well under way to safeguard against extinction. Non-native herbivores and predators, such as goats and cats, had been eradicated from some islands. A significant development in island restoration in the mid-1980s was the eradication of rats from small forested islands. This eradication technology has been refined and currently at least 65 islands, including large and remote Campbell (11 216 ha) and Raoul (2938 ha) Islands, have been successfully cleared of rats. Many of New Zealand's offshore islands, especially those without predatory mammals, are home to large numbers of breeding seabirds. Seabirds influence ecosystem processes on islands by enhancing soil fertility and through soil disturbance by burrowing. Predators, especially rats, alter ecosystem processes and cause population reductions or extinctions of native animals and plants. Islands have been promoted as touchstones of a primaeval New Zealand, but we are now increasingly aware that most islands have been substantially modified since human settlement of New Zealand. Archaeological and palaeoecological investigations, together with the acknowledgement that many islands have been important mahinga kai (sources of food) for Māori, have all led to a better understanding of how people have modified these islands. Restoration technology may have vaulted ahead of our ability to predict the ecosystem consequences of its application on islands. However, research is now being directed to help make better decisions about restoration and management of islands, decisions that take account of island history and key drivers of island ecosystem functioning. Article Full-text available Fifty years ago, GE Hutchinson defined the ecological niche as a hypervolume in n-dimensional space with environmental variables as axes. Ecologists have recently developed renewed interest in the concept, and technological advances now allow us to use stable isotope analyses to quantify these niche dimensions. Analogously, we define the isotopic niche as an area (in δ-space) with isotopic values (δ-values) as coordinates. To make isotopic measurements comparable to other niche formulations, we propose transforming δ-space to p-space, where axes represent relative proportions of isotopically distinct resources incorporated into an animal's tissues. We illustrate the isotopic niche with two examples: the application of historic ecology to conservation biology and ontogenetic niche shifts. Sustaining renewed interest in the niche requires novel methods to measure the variables that define it. Stable isotope analyses are a natural, perhaps crucial, tool in contemporary studies of the ecological niche. Article Full-text available Greenaway, P. 2003. Terrestrial adaptations in the Anomura (Crustacea: Decapoda). In: Lemaitre, R., and Tudge, C.C. (eds), Biology of the Anomura. Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9-13 July 2001. Memoirs of Museum Victoria 60(1): 13-26. In this review, morphological, physiological and behavioural adaptations to life on land by anomurans are considered. The most terrestrial group are the Coenobitidae and these have developed terrestrial adaptations broadly similar to those of the terrestrial brachyurans. The coenobitids have developed two evolutionary, terrestrial lines. Coenobita spp. retain the protective gastropod shell and this has placed a set of constraints on morphological, physiological and behavioural development particularly in regard to gas exchange, osmoregulation and excretion. Birgus do not carry molluscan shells after the juvenile stages and, freed from its constraints, reach larger size and have developed terrestrial adaptations that closely parallel those of the brachyuran land crabs. Shell retention by Coenobita has resulted in development of novel abdominal gas exchange organs whilst purine excretion by B. latro seems to be unique amongst land crabs. Crabs of both genera are well adapted to life on land in terms of sensory, respiratory, excretory and osmoregulatory functions and they can also moult, mate and lay eggs effectively on land. Several species have the functional ability to live in a range of habitats from rainforest to arid scrubland but their penetration of these habitats is limited to small islands or to a narrow coastal strip. This is probably due to the retention of pelagic larval stages and to the lack of molluscan shells of suitable dimensions and strength in inland situations, which restrict the range to a manageable distance from the sea. Article Full-text available Gecarcoidea natalis and Geograpsus grayi are both ammonotelic but excrete ammonia by different routes and mechanisms. In G. natalis ammonium ions in the final excretory fluid (P) constitute 67. 7% of the total nitrogenous output of 38. 11 ± 23.0 SD μmol N · kg⁻¹ · h⁻¹. The urine contains little ammonium (0.36 ± 0.081 SD mmol · L⁻¹) and is released into the branchial chambers where ammonium is added and salts are reabsorbed. When the P is finally released it contains 10.8 ± 7.79 mmol NH⁺₄ · L⁻¹, but individual values as high as 73 mmol *· L⁻¹ have been measured. Starvation lowered the concentration of urea, ammonium, and amino acids in the hemolymph and reduced output of nonprotein nitrogen compounds in the feces. In G. grayi gaseous ammonia accounts for 82.3% of the total nitrogenous excretion of 106. 6 ± 50.3 SD μmol N · kg⁻¹ · h⁻¹. Periods of excretion lasting 1-2 d alternate with similar periods of minimal excretion. Starvation did not alter the rate of ammonia excretion but caused a reduction in output of fecal N and a fall in the concentration of urea in the hemolymph. Article Full-text available Biological invasions are a widespread and significant component of human-caused global environmental change. The extent of invasions of oceanic islands, and their consequences for native biological diversity, have long been recognized. However, invasions of continental regions also are substantial. For example, more than 2,000 species of alien plants are established in the continental United States. These invasions represent a human-caused breakdown of the regional distinctiveness of Earth's flora and fauna - a substantial global change in and of itself. Moreover, there are well-documented examples of invading species that degrade human health and wealth, alter the structure and functioning of otherwise undisturbed ecosystems, and/or threaten native biological diversity. Invasions also interact synergistically with other components of global change, notably land use change. People and institutions working to understand, prevent, and control invasions are carrying out some of the most important - and potentially most effective - work on global environmental change. Article Full-text available Many different drivers, including productivity, ecosystem size, and disturbance, have been considered to explain natural variation in the length of food chains. Much remains unknown about the role of these various drivers in determining food chain length, and particularly about the mechanisms by which they may operate in terrestrial ecosystems, which have quite different ecological constraints than aquatic environments, where most food chain length studies have been thus far conducted. In this study, we tested the relative importance of ecosystem size and productivity in influencing food chain length in a terrestrial setting. We determined that (1) there is no effect of ecosystem size or productive space on food chain length; (2) rather, food chain length increases strongly and linearly with productivity; and (3) the observed changes in food chain length are likely achieved through a combination of changes in predator size, predator behavior, and consumer diversity along gradients in productivity. These results lend new insight into the mechanisms by which productivity can drive changes in food chain length, point to potential for systematic differences in the drivers of food web structure between terrestrial and aquatic systems, and challenge us to consider how ecological context may control the drivers that shape food chain length. Article Full-text available Two terrestrial brachyuran grapsid crabs are recorded from Taveuni ls. in the Fiji group: Sesarma (Sesarmops) impressum and Geograpsus crinipies. These new records, plus previous records of grapsid crabs S. (Parasesarma) lenzii, S. (P.) leptosoma, S. (Labuanium) rotundatum, S. (Neosarntatium) smithii, S. (Labuanium) trapezoidum, S. (Perisesarma) bidens, Geograpsus grayi, Varuna !itterata and the gecarcinid crabs Cardisoma longipes, C. carnifex, C. hirtipes, and Gecarcoidea lalandii, bring the total known Fiji fauna to fourteen species. Further collecting is likely to reveal many more species. Article Full-text available Positive density-dependent seed and seedling predation, where herbivores selectively eat seeds or seedlings of common species, is thought to play a major role in creating and maintaining plant community diversity. However, many herbivores and seed predators are known to exhibit preferences for rare foods, which could lead to negative density-dependent predation. In this study, we first demonstrate the occurrence of increased predation of locally rare tree species by a widespread group of insular seed and seedling predators, land crabs. We then build computer simulations based on these empirical data to examine the effects of such predation on diversity patterns. Simulations show that herbivore preferences for locally rare species are likely to drive scale-dependent effects on plant community diversity: at small scales these foraging patterns decrease plant community diversity via the selective consumption of rare plant species, while at the landscape level they should increase diversity, at least for short periods, by promoting clustered local dominance of a variety of species. Finally, we compared observed patterns of plant diversity at the site to those obtained via computer simulations, and found that diversity patterns generated under simulations were highly consistent with observed diversity patterns. We posit that preference for rare species by herbivores may be prevalent in low- or moderate-diversity systems, and that these effects may help explain diversity patterns across different spatial scales in such ecosystems. Article Full-text available Study of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society. Article Full-text available Assumptions behind optimal foraging theory are: 1) an individual's contribution to the next generation (its fitness) depends on behaviour during foraging; 2) there should be a heritable component of foraging behaviour (the actual innate foraging responses or the rules by which such responses are learned), and the proportion of individuals in a population foraging in ways that enhance fitness will tend to increase over time; 3) the relationship between foraging behaviour and fitness is known; 4) evolution of foraging behaviour is not prevented by genetic contraints; 5) such evolution is subject to 'functional' constraints (eg related to the animal's morphology); and 6) foraging behaviour evolves more rapidly than the rate at which relevant environmental conditions change. The review considers recent theoretical and empirical developments, dealing with behaviour of animals while they are foraging (but ignoring the timing of and the amount of time allocated to such behaviour). Ideas considered include risk aversion and risk proneness; optimal diet; optimal patch choice; optimal patch departure rules; optimal movements; and optimal central place foraging. Means of evaluating optimal foraging theory are discussed. -P.J.Jarvis Article Full-text available Invasive rodents are among the most ubiquitous and problematic species introduced to islands; more than 80% of the world’s island groups have been invaded. Introduced rats (black rat, Rattus rattus; Norway rat, R. norvegicus; Pacific rat, R. exulans) are well known as seed predators but are often overlooked as potential seed dispersers despite their common habit of transporting fruits and seeds prior to consumption. The relative likelihood of seed predation and dispersal by the black rat, which is the most common rat in Hawaiian forest, was tested with field and laboratory experiments. In the field, fruits of eight native and four non-native common woody plant species were arranged individually on the forest floor in four treatments that excluded vertebrates of different sizes. Eleven species had a portion (3–100%) of their fruits removed from vertebrate-accessible treatments, and automated cameras photographed only black rats removing fruit. In the laboratory, black rats were offered fruits of all 12 species to assess consumption and seed fate. Seeds of two species (non-native Clidemia hirta and native Kadua affinis) passed intact through the digestive tracts of rats. Most of the remaining larger-seeded species had their seeds chewed and destroyed, but for several of these, some partly damaged or undamaged seeds survived rat exposure. The combined field and laboratory findings indicate that many interactions between black rats and seeds of native and non-native plants may result in dispersal. Rats are likely to be affecting plant communities through both seed predation and dispersal. KeywordsBlack rat–Captive feeding trials–Frugivory–Islands–Rodent–Seed size Article Full-text available Introduced rats (Rattus spp.) can affect island vegetation structure and ecosystem functioning, both directly and indirectly (through the reduction of seabird populations). The extent to which structure and function of islands where rats have been eradicated will converge on uninvaded islands remains unclear. We compared three groups of islands in New Zealand: islands never invaded by rats, islands with rats, and islands on which rats have been controlled. Differences between island groups in soil and leaf chemistry and leaf production were largely explained by burrow densities. Community structure of woody seedlings differed by rat history and burrow density. Plots on islands with high seabird densities had the most non-native plant species. Since most impacts of rats were mediated through seabird density, the removal of rats without seabird recolonization is unlikely to result in a reversal of these processes. Even if seabirds return, a novel plant community may emerge. Article Full-text available Invasions of alien rodents have shown to have devastating effects on insular ecosystems. Here we review the ecological impacts of these species on the biodiversity of the Balearic and the Canary Islands. A total of seven species of introduced rodents (two rats, three mice, one dormouse, and one squirrel) have been recorded (six in the Balearics and four in the Canaries). Some of them can occasionally be important predators of nesting seabirds, contributing to the decline of endangered populations in both archipelagos. Rats are also known to prey upon terrestrial birds, such as the two endemic Canarian pigeons. Furthermore, rats actively consume both vegetative and reproductive tissues of a high number of plants, with potential relevant indirect effects on vegetation by increasing erosion and favoring the establishment of alien plants. In the Balearics, rats and mice are important seed predators of endemic species and of some plants with a restricted distribution. In the Canaries, rats intensively prey upon about half of the fleshy-fruited tree species of the laurel forest, including some endemics. In both archipelagos, alien rodents disrupt native plant–seed dispersal mutualisms, potentially reducing the chances of plant recruitment at the same time that they modify the structure of plant communities. We further suggest that alien rodents played (and play) a key role in the past and present transformation of Balearic and Canarian native ecosystems. Article Full-text available Introduced rats are now being eradicated from many islands. Increasingly, these eradications are contested by activists claiming moral, legal, cultural, historic or scientific reasons and poorly documented evidence of effects. We reviewed the global literature on the effects of rats on island flora and fauna. We then used New Zealand as a case study because of its four-decade history of rat eradications and many detailed and innovative studies of how rats affect native species. These include use of exclosures, local manipulations of rat populations, video surveillance, and measurements of responses following eradications. The most intensive studies have been on the Pacific rat (Rattus exulans), a small South-East Asian species spread by Polynesians throughout the Pacific. These and the more recently introduced Norway rat (R. norvegicus) and ship (roof) rat (R. rattus) suppress some forest plants, and are associated with extinctions or declines of flightless invertebrates, ground-dwelling reptiles, land birds, and burrowing seabirds. On islands off France, Norway rats are also implicated in declines of shrews. Globally, ship rats were associated with declines or extinctions of the largest number of indigenous vertebrate species (60), including small mammals such as deer mice and bats. Effects of rats on forest trees and seabird populations are sufficiently pervasive to affect ecosystem structure and function. However, the data are patchy. Deficiencies in our knowledge would be reduced by documenting distribution and abundance of indigenous species before and after eradications. Comprehensive measurements of the responses of indigenous species to rat eradications would enable the development of testable models of rat invasion effects. Article Full-text available The stable isotopes of nitrogen (d15N) and carbon (d13C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how d 15N and d13C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of d15N is 3.4‰ (1 SD 5 1‰) and of d13 Ci s 0.4‰ (1 SD 5 1.3‰), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of d15N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of d13C when d13C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions Code Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes. [Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN]. Article The eradication of invasive species from islands is a conservation intervention proven to protect biodiversity, with more than 1200 successful vertebrate eradications implemented globally. The demand for eradication projects is increasing and practitioners are planning projects on increasingly larger, more remote and more technically challenging islands. Undertaking strategic planning for conservation requires information on both the cost and benefit of proposed actions, to determine the trade-off in selecting one project over another. To date the cost of eradication projects is disparately reported in the literature, an artefact of different reporting requirements based on where the eradication was undertaken, the scale of the project, the implementing agency and its accountabilities, and inconsistency in reporting all project component costs. Eradication projects have characteristics that allow more refined cost forecasting relative to other conservation initiatives, including a narrow set of major eradication techniques being used, a defined beginning and end point, and distinct project components. Here we present the major cost centres for eradication projects, including a dataset for a suite of rodent, ungulate and predator eradications, using a dataset of 46 eradications primarily from New Zealand, Ecuador and the USA. We found cost increased with island size for all eradication types except ground based rodent eradications. Using these standards to report project costs will improve the ability to evaluate and predict the cost of removing invasive animals from islands to protect native insular biodiversity. Article The importance of local dispersal to Pandanus tectorius Park. ex Z. (Pandanaceae) is assessed by analyzing the spatial distribution of juveniles. Juveniles are, on average, further away from adults than undispersed seeds; and older juveniles are at a greater distance than seedlings. These results indicate the importance of local dispersal to successful reproduction. The agent of this dispersal is a land crab, Cardisoma carnifex (Herbst.). C. carnifex readily locates and eats the fruit of Pandanus tectorius. Crabs transport the fruit before consuming it, and discard the woody portion which contains the seeds, thus serving as dispersal agents. Experiments show the distance crabs may carry the fruit varies widely and averages 7.3 m in this study. /// Значение локальной дисперсии для Pandanus tectorius Park ex Z. (Pandanaceae) оценивали методоманализа пространственного распределения ювенильных особей. Молодые растения в среднем удалены от взрослых на большее расстояние, чем нерассеянные семена, а ювенильные растения более старшего возраста находились на большем удалении, чем всхобы. Эти результаты показывают значение локальной дисперсии для репродуктивного успеха. Агентом зтой дисперсии оказывается наземный краб Cardisoma carnifex (Herbst). C. carnifex локализуется поблизости и питается плодами Pandanus tectorius. Крабы перемещают плоды перед тем, как их сьесть, и выбрасывают одревесневшие части, содержащие семена, действуя таким образом, как агенты расселения. Опыты показали, что дистанция переноса плодов крабами может широко варьировать; в среднем она составляет в данном исследовании 7,3 м. Article Arthur Mellows Village College believes strongly in supporting student mental health. SENCO Sara Parnell discusses their variety of approaches. Article With the rise of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has rapidly increased in ecology. Such models are static and probabilistic in nature, since they statistically relate the geographical distribution of species or communities to their present environment. A wide array of models has been developed to cover aspects as diverse as biogeography, conservation biology, climate change research, and habitat or species management. In this paper, we present a review of predictive habitat distribution modeling. The variety of statistical techniques used is growing. Ordinary multiple regression and its generalized form (GLM) are very popular and are often used for modeling species distributions. Other methods include neural networks, ordination and classification methods, Bayesian models, locally weighted approaches (e.g. GAM), environmental envelopes or even combinations of these models. The selection of an appropriate method should not depend solely on statistical considerations. Some models are better suited to reflect theoretical findings on the shape and nature of the species’ response (or realized niche). Conceptual considerations include e.g. the trade-off between optimizing accuracy versus optimizing generality. In the field of static distribution modeling, the latter is mostly related to selecting appropriate predictor variables and to designing an appropriate procedure for model selection. New methods, including threshold-independent measures (e.g. receiver operating characteristic (ROC)-plots) and resampling techniques (e.g. bootstrap, cross-validation) have been introduced in ecology for testing the accuracy of predictive models. The choice of an evaluation measure should be driven primarily by the goals of the study. This may possibly lead to the attribution of different weights to the various types of prediction errors (e.g. omission, commission or confusion). Testing the model in a wider range of situations (in space and time) will permit one to define the range of applications for which the model predictions are suitable. In turn, the qualification of the model depends primarily on the goals of the study that define the qualification criteria and on the usability of the model, rather than on statistics alone. Article Ecologists have long struggled to explain variation in food-chain length among natural ecosystems. Food-chain length is predicted to be shorter in ecosystems subjected to greater disturbance because longer chains are theoretically less resilient to perturbation. Moreover, food-chain length is expected to be longer in larger ecosystems because increasing ecosystem size increases species richness and stabilizes predator-prey interactions, or increases total resource availability. Here we test the roles of disturbance and ecosystem size in determining the food-chain length of terrestrial food webs on Bahamian islands. We found that disturbance affected the identity of top predators, but did not change food-chain length because alternative top predators occupied similar trophic positions. On the other hand, a 106- fold increase in ecosystem size elevated food-chain length by one trophic level. We suggest that the effect of disturbance on food-chain length is weak when alternate top predators are trophic omnivores and have similar trophic positions. This and previous work in lakes suggest that ecosystem size may be a strong determinant of food-chain length in both aquatic and terrestrial ecosystems. Article We tested the hypothesis that an omnivorous land crab determines the dynamics of seedling recruitment in rain forest on Christmas Island, Indian Ocean. The red crab (Gecarcoidea natalis) occurs at densities of ~ 1 crab/m2 and consumes seeds, seedlings, and leaf litter. A crab-exclusion experiment below closed canopy and in light gaps showed that red crabs markedly reduced seedling recruitment. Overall, seedling emergence was 29-fold and 21-fold greater on the exclusion plots in the understory and in gaps, respectively. In control plots, mean seedling densities never exceeded 15 seedlings/25 m2 in the understory and 3 seedlings/25 m2 in gaps. Species richness of seedlings was significantly higher in the absence of crabs, averaging >10 and 12 species per plot in the understory and gaps, respectively. On control plots, mean species richness was less than one species per plot. Two-dimensional ordination (using nonmetric multidimensional scaling) showed that red crabs had a large impact on relative species abundances. Analyses of similarity confirmed that significant differences existed between both treatments and habitats. Seed removal and seedling transplant experiments suggested that most rain forest species are rapidly eaten by red crabs. Seedlings of many of these vulnerable species (e.g., Maclura cochinchinensis, Planchonella nitida, Schefflera elliptica) were abundant on exclusion plots. However, they were rare on control plots, and none persisted for >2 mo. Persistent seedlings were limited to two species (Inocarpus fagifer and Tristiropsis acutangula), both of which were resistant as seeds and seedlings to crab predation. Although red crabs are the major biotic determinants of seedling recruitment, this impact was not reflected in the overhead canopy. Some tree species unable to recruit in the presence of crabs were common as adults. Shifting mosaics in crab densities over space and time may offer the best explanation for recruitment of vulnerable species. Our results show that a dominant consumer has large effects on plant community structure on a remote oceanic island, consistent with the viewpoint that strong control by a single species is more likely in simple communities. Article Land crabs are the largest terrestrial invertebrates on Aldabra. The 12 species occupy most trophic levels, and some crabs are responsible for the transfer of energy from land to sea and vice versa. Some species may be responsible for preventing, or severely reducing colonization of Aldabra by exotic plant species. Other species are important in hastening leaf litter breakdown by digestion, while scavenging forms reduce the number of carrion-breeding flies. Burrowing forms may aerate the soil, and the littoral crab, Grapsus tenuicrustatus, by feeding on surface encrusting alga may speed erosion and aid soil formation. The hermit crabs form an important part of the diet of the flightless rail, and by depositing gastropod shells on land may provide drinking and breeding places for other animals. Article Field experiments comparing leaf-fall in the presence and absence of the red land crab, Gecarcoidea natalis, in rain forest on Christmas Island, Indian Ocean showed that, by eating and returning leaves to their burrows, they significantly reduced accumulation of leaf-fall on the forest floor. Red crabs removed 30–50% of the leaf-fall at the experimental sites during the study. Differences in leaf-fall mass between crab-access and exclusion quadrats were positively correlated with the density of foraging red crabs. Red crabs also generated spatial heterogeneity in the distribution of litter on the forest floor by returning litter to their burrows. Leaves lined chambers of 64% of excavated burrows and litter biomass around the entrances was significantly greater than that on off-burrow locations. This was reflected in the significantly higher concentrations of organic matter and nutrients (N, P, K, Ca, Na, and Mg) associated with soils near burrow entrances. These results suggest that a single species, G. natalis, is the major processor of leaf-fall in rain forest on Christmas Island and may affect (1) the temporal and spatial patterns of nutrient availability and (2) the diversity and biomass of the litter fauna. Article Stable isotope analysis (SIA) has proven to be a useful tool in reconstructing diets, characterizing trophic relationships, elucidating patterns of resource allocation, and constructing food webs. Consequently, the number of studies using SIA in trophic ecology has increased exponentially over the past decade. Several subdisciplines have developed, including isotope mixing models, incorporation dynamics models, lipid-extraction and correction methods, isotopic routing models, and compound-specific isotopic analysis. As with all tools, there are limitations to SIA. Chief among these are multiple sources of variation in isotopic signatures, unequal taxonomic and ecosystem coverage, over-reliance on literature values for key parameters, lack of canonical models, untested or unrealistic assumptions, low predictive power, and a paucity of experimental studies. We anticipate progress in SIA resulting from standardization of methods and models, calibration of model parameters through experimentation, and continued development of several recent approaches such as isotopic routing models and compound-specific isotopic analysis. Article Many of the world's oceanic and oceanic-like islands possessed endemic mammal faunas before they were colonized by humans. These faunas, unbalanced and impoverished compared to continental faunas, usually lacked large mammalian carnivores. In virtually all cases, the arrival of humans and their domesticants and commensals on these islands is related to the extirpation of large numbers of endemic insular mammals. These extinction events affected at least 27% of autochthonous mammal species on the world's oceanic and oceanic-like islands. This percentage rises the 35% when volant mammals are excluded. This reduction in the natural biodiversity brought about the disappearance of several unique biological types that apparently never existed on the continents. Article Birgus latro (L.) is the largest terrestrial hermit crab in the world. The species is widely distributed on remote Indo-Pacific islands of the tropics, but it is rapidly declining and is currently classified as data deficient on the IUCN red list. This review provides a synopsis of both published and unpublished data on the biology and ecology of B. latro. It highlights the lack of robust biological information on the species’ basic biology, particularly in the juvenile and reproductive phases, while behavioural ecology studies are few and report conflicting data between populations. Population studies indicate that B. latro may have limited recruitment events throughout its range, emphasising the need for more systematic research to clearly identify factors that influence successful recruitment events. The review highlights the paucity of substantiated peer reviewed studies on this species and emphasises the need for further systematic research. Article Summary • Owing to the detrimental impacts of invasive alien species, their control is often a priority for conservation management. Whereas the potential for unforeseen consequences of management is recognized, their associated complexity and costs are less widely appreciated. • We demonstrate that theoretically plausible trophic cascades associated with invasive species removal not only take place in reality, but can also result in rapid and drastic landscape-wide changes to ecosystems. • Using a combination of population data from of an invasive herbivore, plot-scale vegetation analyses, and satellite imagery, we show how a management intervention to eradicate a mesopredator has inadvertently and rapidly precipitated landscape-wide change on sub-Antarctic Macquarie Island. This happened despite the eradication being positioned within an integrated pest management framework. Following eradication of cats Felis catus in 2001, rabbit Oryctolagus cuniculus numbers increased substantially although a control action was in place (Myxoma virus), resulting in island-wide ecosystem effects. • Synthesis and applications. Our results highlight an important lesson for conservation agencies working to eradicate invasive species globally; that is, risk assessment of management interventions must explicitly consider and plan for their indirect effects, or face substantial subsequent costs. On Macquarie Island, the cost of further conservation action will exceed AU$24 million.
Article
Eradications of invasive species often have striking positive effects on native biota. However, recent research has shown that species removal in isolation can also result in unexpected changes to other ecosystem components. These secondary effects will become more likely as numbers of interacting invaders increase in ecosystems, and as exotics in late stages of invasion eliminate native species and replace their functional roles. Food web and functional role frameworks can be used to identify ecological conditions that forecast the potential for unwanted secondary impacts. Integration of eradication into a holistic process of assessment and restoration will help safeguard against accidental, adverse effects on native ecosystems.