Aaron B. Shiels

Are introduced rats (Rattus rattus) both seed predators and dispersers in Hawaii

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.

Landsliding and Its Multiscale Influence on Mountainscapes

Landsliding is a complex process that modifies mountainscapes worldwide. Its severe and sometimes long-lasting negative effects contrast with the less-documented positive effects on ecosystems, raising numerous questions about the dual role of landsliding, the feedbacks between biotic and geomorphic processes, and, ultimately, the ecological and evolutionary responses of organisms. We present a conceptual model in which feedbacks between biotic and geomorphic processes, landslides, and ecosystem attributes are hypothesized to drive the dynamics of mountain ecosystems at multiple scales. This model is used to integrate and synthesize a rich, but fragmented, body of literature generated in different disciplines, and to highlight the need for profitable collaborations between biologists and geoscientists. Such efforts should help identify attributes that contribute to the resilience of mountain ecosystems, and also should help in conservation, restoration, and hazard assessment. Given the sensitivity of mountains to land-use and global climate change, these endeavors are both relevant and timely.

Biology and impacts of Pacific island invasive species. 11. Rattus rattus, the black rat (Rodentia: Muridae).

Abstract: 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.

Germination after simulated rat damage in seeds of two endemic Hawaiian palm species

Seed predation by native and alien rodents can limit plant recruitment and ultimately affect forest dynamics and composition (Campbell & Atkinson 2002, Cote et al . 2003, Hulme 1998, Sanchez-Cordero & Martinez-Gallardo 1998). Even partial consumption of seeds by predators may affect plant community structure, though its importance is poorly understood (Steele et al . 1993, Vallejo-Marin et al . 2006). Despite consumption of relatively large portions of seeds by herbivores, seeds can retain their ability to germinate if the embryo remains intact (Dalling & Harms 1999, Janzen 1972, Mack 1998). Germination of damaged seeds may be accelerated or prolonged (Karban & Lowenberg 1992, Koptur 1998, Vallejo-Marin et al . 2006). Damage by seed pests also facilitates ageing stress; which manifests as decreased seedling vigour, decreased seed viability, lower germination percentages and slower germination rates (Priestley 1986).

Applying lessons from ecological succession to the restoration of landslides

Landslides are excellent illustrations of the dynamic interplay of disturbance and succession. Restoration is difficult on landslide surfaces because of the high degree of spatial and temporal heterogeneity in soil stability and fertility. Principles derived from more than a century of study of ecological succession can guide efforts to reduce chronic surface soil erosion and restore both biodiversity and ecosystem function. Promotion of the recovery of self-sustaining communities on landslides is feasible by stabilization with native ground cover, applications of nutrient amendments, facilitation of dispersal to overcome establishment bottlenecks, emphasis on functionally redundant species and promotion of connectivity with the adjacent landscape. Arrested succession through resource dominance by a single species can be beneficial if that species also reduces persistent erosion, yet the tradeoff is often reduced biodiversity. Restoration efforts can be streamlined by using techniques that promote successional processes.

Changes in abiotic influences on seed plants and ferns during 18 years of primary succession on Puerto Rican landslides

Summary 1. Abiotic variables are critical drivers of succession in most primary seres, but how their influence on biota changes over time is rarely examined. Landslides provide good model systems for examining abiotic influences because they are spatially and temporally heterogeneous habitats with distinct abiotic and biotic gradients and post-landslide erosion. 2. In an 18-year study on 6 Puerto Rican landslides, we used structural equation models to interpret the changing effects of abiotic influences (landslide dimensions, slope, aspect, elevation, parent material and related soil properties) on seed plants (density and diversity), tree fern density, scrambling fern cover, canopy openness and soil development (nitrogen, soil organic matter, pH and cation exchange capacity). 3. Seven years after landslide formation, catchment size (the landslide area above the point of measurement) was the key abiotic factor influencing plants. The larger the catchment the greater was the diversity and density of seed plants. Conversely, the smaller the catchment the greater was the density of tree ferns and the cover of scrambling ferns. 4. Eighteen years after landslide formation, landslide slope was the key abiotic influence. The greater the slope, the lower was the density and diversity of seed plants and the greater was the scrambling fern cover. 5. Aspect, particularly east-facing slopes exposed to wind disturbances, positively influenced tree fern densities at both 7 and 18 years and negatively influenced seed plants and scrambling ferns at 18 years. Soils were least developed, that is, had lowest soil nitrogen and organic matter concentrations, after 18 years on steep slopes (like seed plants); soils were most developed near landslide edges, on hurricane-exposed slopes (like tree ferns) and where there were high soil potassium concentrations. 6. Synthesis. Abiotic variables have important influences on plant succession on landslides and the relative influence of different abiotic variables changes with time. Improved predictability of temporal dynamics will rely not only on understanding the effects of initial disturbances and subsequent biological responses but also on the different and changing influences exerted by each abiotic variable.

Detection of Angiostrongylus cantonensis in the Blood and Peripheral Tissues of Wild Hawaiian Rats (Rattus rattus) by a Quantitative PCR (qPCR) Assay.

The nematode Angiostrongylus cantonensis is a rat lungworm, a zoonotic pathogen that causes human eosinophilic meningitis and ocular angiostrongyliasis characteristic of rat lungworm (RLW) disease. Definitive diagnosis is made by finding and identifying A. cantonensis larvae in the cerebral spinal fluid or by using a custom immunological or molecular test. This study was conducted to determine if genomic DNA from A. cantonensis is detectable by qPCR in the blood or tissues of experimentally infected rats. F1 offspring from wild rats were subjected to experimental infection with RLW larvae isolated from slugs, then blood or tissue samples were collected over multiple time points. Blood samples were collected from 21 rats throughout the course of two trials (15 rats in Trial I, and 6 rats in Trial II). In addition to a control group, each trial had two treatment groups: the rats in the low dose (LD) group were infected by approximately 10 larvae and the rats in the high dose (HD) group were infected with approximately 50 larvae. In Trial I, parasite DNA was detected in cardiac bleed samples from five of five LD rats and five of five HD rats at six weeks post-infection (PI), and three of five LD rats and five of five HD rats from tail tissue. In Trial II, parasite DNA was detected in peripheral blood samples from one of two HD rats at 53 minutes PI, one of two LD rats at 1.5 hours PI, one of two HD rats at 18 hours PI, one of two LD rats at five weeks PI and two of two at six weeks PI, and two of two HD rats at weeks five and six PI. These data demonstrate that parasite DNA can be detected in peripheral blood at various time points throughout RLW infection in rats.

Control of invasive rats on islands and priorities for future action

Invasive rats are one of the worlds most successful animal groups that cause native species extinctions and ecosystem change, particularly on islands. On large islands, rat eradication is often impossible and population control, defined as the local limitation of rat abundance, is now routinely performed on many of the worlds islands as an alternative management tool. However, a synthesis of the motivations, techniques, costs, and outcomes of such rat-control projects is lacking. We reviewed the literature, searched relevant websites, and conducted a survey via a questionnaire to synthesize the available information on rat-control projects in island natural areas worldwide to improve rat management and native species conservation. Data were collected from 136 projects conducted over the last 40 years; most were located in Australasia (46%) and the tropical Pacific (25%) in forest ecosystems (65%) and coastal strands (22%). Most of the projects targeted Rattus rattus and most (82%) were aimed at protecting birds and endangered ecosystems. Poisoning (35%) and a combination of trapping and poisoning (42%) were the most common methods. Poisoning allows for treatment of larger areas, and poison projects generally last longer than trapping projects. Second-generation anticoagulants (mainly brodifacoum and bromadiolone) were used most often. The median annual cost for rat-control projects was US

Diverse examples from managing invasive vertebrate species on inhabited islands of the United States

17,262 or US

Capillaria hepatica infection in black rats (Rattus rattus) on Diego Garcia, British Indian Ocean Territory.

227/ha. Median project duration was 4 years. For 58% of the projects, rat population reduction was reported, and 51% of projects showed evidence of positive effects on biodiversity. Our data were from few countries, revealing the need to expand rat-control distribution especially in some biodiversity hotspots. Improvement in control methods is needed as is regular monitoring to assess short- and long-term effectiveness of rat-control.