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Abstract The salt marsh harvest mouse (Reithrodontomys raviventris; RERA) is an endangered species endemic to the coastal wetlands of the San Francisco Estuary, California. RERA are specialized to saline coastal wetlands, and their historical range has been severely impacted by landscape conversion and the introduction of non‐native plant and rodent species. A better understanding of their diet is needed to assess habitat quality, particularly in relation to potential competitors. We investigated three questions using DNA metabarcoding with ITS2 and trnL markers: (1) Do RERA specialize on the native plant, pickleweed (Salicornia pacifica), (2) Do RERA consume non‐native plants, and (3) What is the dietary niche breadth and overlap with three sympatric native and non‐native rodents? RERA diet was dominated by two plants, native Salicornia and non‐native salt bush (Atriplex spp.), but included 48 plant genera. RERA diet breadth was narrowest in fall, when they consumed the highest frequencies of Salicornia and Atriplex, and broadest in spring, when the frequencies of these two plants were lowest. Diet breadth was slightly lower for RERA than for co‐occurring species in pairwise comparisons. All four species consumed similarly high frequencies of wetland plants, but RERA consumed fewer grasses and upland plants, suggesting that it may be less suited to fragmented habitat than sympatric rodents. Diet overlap was lowest between RERA and the native California vole (Microtis californicus). In contrast, RERA diet overlapped substantially with the native western harvest mouse (R. megalotis) and non‐native house mouse (Mus musculus), suggesting potential for competition if these species become sufficiently abundant.

Tree squirrels (Sciurus spp.) are highly successful immigrants to urban and suburban areas in North America and Europe, causing both economic and ecological damage. Control of such invasive populations is challenging but of increasing importance to local managers. We studied an invasive population of fox squirrels (S. niger) and applied an immunocontraceptive vaccine in an experimental study of demographic control. Here we integrate our data into a simple stage-structured population model to simulate population reduction under 2 treatment levels (60 and 80% of females, respectively) for vaccines lasting from 1 to 5 years. Contraception can be an effective means of reducing fox squirrel populations if the vaccine is effective for ≥2 years or if ≥71% of the females are treated. Over a 15-year period, fewer individuals require treatment at a treatment rate of 0.8 versus 0.6 due to a declining population size. This study illustrates how a simple population model may guide local resource managers in the design of control strategies for invasive species.

Four recent studies on Chilean vertebrates underscore the very different effects that habitat fragmentation may have under different conditions. In southern Chile, birds exhibited significant species-area relationships, whereas the more depauperate small mammal community did not. The avifauna of highly isolated rainforest remnants in Fray Jorge National Park (IV Región) presented steeper species-area relations than those in southern Chile, reminiscent of land-bridge islands after faunal relaxation. The small mammal results were unexpected but may reflect the reduced vagility and immigration potential of this group. Additionally, the inter-remnant matrix habitat may support large populations of only some species, allowing them to capitalize on resources that are available in forest remnants. Such an effect is less likely for birds due to their greater vagility. Although the influence of remnant area is more clearly demonstrated for birds in Chile, it appears that small mammal assemblages may be more immediately impacted by habitat fragmentation than are birds, and that further fragmentation of temperate rainforests will seriously impoverish the small mammal assemblage, many of whose members are endemic to this region. Further research should emphasize the role of the inter-remnant matrix, of habitat corridors, and of the relative sensitivity of different species to matrix/corridor quality and remnant isolationCuatro estudios recientes en vertebrados chilenos subrayan los efectos muy diversos que la fragmentación del hábitat puede tener bajo diversas condiciones. En el sur de Chile, las aves exhibieron relaciones significativas entre la riqueza de especies y el área de hábitat ("especies-area"), mientras que tal relación no se observó en la comunidad de pequeños mamíferos, la cual tiene menos especies. La avifauna de los fragmentos remanentes altamente aislados del Parque Nacional Fray Jorge (IV Región) presentaron relaciones especies-área más pronunciadas que aquellas de Chile meridional. Lo observado para los pequeños mamíferos fue inesperado aunque puede reflejar un menor potencial de movilidad e inmigración en este grupo. Además, el hábitat de la matriz inter-fragmento puede albergar solo a poblaciones grandes de algunas especies, lo que les permitiría capitalizar los recursos que están disponibles en los fragmentos de bosque. Tal efecto es menos probable para el caso de las aves producto de su mayor movilidad. Aunque la influencia del área de los fragmentos remanentes es más claro en el caso de las aves en Chile, es probable que los ensambles de mamíferos pequeños sean más afectados en el corto plazo por la fragmentación del hábitat que las aves, y que una fragmentación adicional de los bosques templados lluviosos determinará un mayor empobrecimiento de los ensambles de pequeños mamíferos, muchos de los cuales son endémicos en esta región. Estudios adicionales deberían enfatizar el papel de la matriz ínter-fragmento, el de los corredores de hábitat, y evaluar la sensibilidad relativa de diversas especies al aislamiento de los fragmentos remanentes y a la calidad de la matriz/corredor

Low risk for hantavirus pulmonary syndrome (HPS) has been reported among biologists engaged in fieldwork with rodents. The overall probability of acquiring HPS when working with rodents appears to be 1 in 1,412 (0.00071). Nonetheless, a causal link between HPS and lack of personal protective equipment (PPE) use is suggested by some investigators. However, supporting data are incomplete and consequently misleading. A recent HPS case was assumed to be acquired during rodent-handling activities, although substantial peridomestic exposure was evident. Regulatory groups interpret inadequate data as evidence of the need for rigorous PPE, which can hamper field research and instructional efforts. PPE recommendations should be reviewed and revised to match the risk associated with different types of fieldwork with small mammals.

Since 1989, we have conducted a large-scale ecological experiment in semiarid thorn scrub of a national park in north-central Chile. Initially, we focused on the role of biotic interactions including predation, interspecific competition, and herbivory in small mammal and plant components of the community. We utilized a reductionist approach with replicated 0.56 ha fenced grids that selectively excluded vertebrate predators and/or larger small mammal herbivores such as the degu, Octodon degus. Although we detected small transitory effects of predator exclusions on degu survival and numbers, other species failed to show responses. Similarly, interspecific competition (i.e., degus with other small mammals) had no detectable numerical effects (although some behavioral responses occurred), and degu-exclusions had relatively small effects on various plant components. Modeling approaches indicate that abiotic factors play a determining role in the dynamics of principal small mammal species such as O. degus and the leaf-eared mouse (Phyllotis darwini). In turn, these are mainly related to aperiodic pulses of higher rainfall (usually during El Niño events) which trigger ephemeral plant growth; a food addition experiment in 1997-2000 verified the importance of precipitation as a determinant of food availability. Since 2004, we have expanded long-term monitoring efforts to other important community components including birds and insects in order to understand effects of abiotic factors on them; we report some of the first results of comprehensive surveys on the former in this region. Finally, we recently shifted focus to documenting effects of exotic lagomorphs in the park. We installed additional treatments selectively excluding small mammals, lagomorphs, or both, from replicated grids in order to evaluate putative herbivore impacts. In conjunction with increased annual rainfall since 2000, we predict that introduced lagomorphs will have increasing impacts in this region, and that more frequent El Niños in conjunction with global climatic change may lead to marked changes in community dynamics. The importance of long-term experimental studies is underscored by the fact that only now after 20 years of work are some patterns becoming evident.Desde 1989 hemos llevado a cabo un experimento ecológico a gran escala en un matorral espinoso semiárido de un parque nacional en el norte de Chile. Inicialmente, nos centramos en el rol de las interacciones bióticas incluyendo depredación, competencia interespecífica y herbivoría en micromamíferos y componentes vegetales de la comunidad. Usamos una aproximación reduccionista con parcelas replicadas cercadas de 0.56 ha que selectivamente excluían depredadores vertebrados y/o micromamíferos herbívoros más grandes como el degu, Octodon degus. Aunque detectamos efectos transitorios menores en la sobrevivencia y número de degus en las exclusiones de depredadores, otras especies no mostraron respuestas. Similarmente, la competencia interespecífica (i.e., degus con otros micromamíferos) no tenía efectos numéricos detectables (aunque ocurrieron algunas respuestas conductuales), y las exclusiones tuvieron efectos relativamente pequeños en varios componentes vegetales. Aproximaciones basadas en modelos indican que los factores abióticos juegan un papel determinante en la dinámica de las especies de micromamíferos principales como O. degus y la laucha orejuda (Phyllotis darwini). En cambio, estos están principalmente relacionados a pulsos no periódicos de lluvias más altas (usualmente durante los eventos El Niño) que gatilla el crecimiento de plantas efímeras; un experimento de adición de alimento en 1997-2000 verificó la importancia de la precipitación como un determinante de la disponibilidad de alimento. Desde el 2004 hemos expandido los esfuerzos de monitoreo de largo plazo a otros componentes comunitarios importantes incluyendo aves e insectos con el fin de entender los efectos de los factores abióticos sobre ellos; informamos algunos de los primeros resultados de censos comprehensivos de aves en esta región. Finalmente, hace poco cambiamos de foco para documentar el efecto de lagomorfos exóticos en el parque. Instalamos tratamientos adicionales excluyendo selectivamente micromamíferos, lagomorfos, o ambos, de parcelas replicadas con el fin de evaluar impactos de herbívoros. En conjunto con el aumento de la precipitación anual desde 2000, predecimos que los lagomorfos introducidos tendrán mayores impactos en esta región y que más frecuentes El Niño en combinación con el cambio climático global puede conducir a cambios marcados en la dinámica comunitaria. La importancia de experimentos de largo plazo es destacado por el hecho que solamente ahora después de 20 años de trabajo algunos patrones están siendo evidentes.