AimTo provide the first analysis of predictors of both establishment and spread, both within and across taxa, for all vertebrate taxa within a region. We used Florida, USA, as our study system because it has a well-documented history of introduction and invasion, and is a hotspot for biological invasions.Location Florida, USA. MethodsWe analysed non-indigenous species (NIS) data from peninsular Florida -which included both successful and unsuccessful introductions from all vertebrate classes -to determine the best predictors of both establishment and spread for fish (65 species), herpetofauna (63 species), birds (71 species) and mammals (25 species). We used 10 variables proposed to be associated with the establishment and spread of NIS: body mass, geographic origin, reproductive rate, diet generalism, native-range size, latitude of native range, number of NIS present at date of introduction, presence of NIS congeners, morphological proximity to other NIS (in terms of body mass) and propagule pressure. A multimodel selection process was used with an information-theoretic approach to determine the best fit models for predicting establishment and spread of NIS. We selected a priori plausible predictive models for establishment and spread.Results Large native-range size and small body mass best predicted establishment of non-indigenous herpetofauna. The presence of NIS congeners had the largest positive effect on the establishment of non-indigenous fish. For mammals, the number of NIS present at the time of introduction best explained establishment. No single model best explained bird establishment. For all taxa but birds, the number of NIS present at time of introduction was included in at least one of the best-supported models for explaining spread.Main conclusions Our analyses suggest that predictors of establishment and spread differ across vertebrate taxa at the scale studied. Most predictive variables can be interpreted as measures of competitive interactions among species.
In the past 20 yr, populations of Cicindela hirticollis Say (Coleoptera: Cicindelidae) that inhabit river shorelines have declined dramatically. These habitats have routinely ßooded in winter and spring historically, but they have been altered by damming and controlled water releases for irrigation and power generation. We tested the ability of C. hirticollis larvae from two river and one bayshore population to survive immersion in severely hypoxic water. This is the Þrst report of population-level differences among insects in immersion survival and likely relates to exposure to different ßooding regimes. The larvae from the Chesapeake Bay population survived Ϸ3 d of immersion, and those from river populations survived about a day longer. Despite survival differences between riverine and seashore populations, recovery times after exposure to severe hypoxia were comparable. Second and third instars from the seashore population had similar survival at 9.0 and 16.5ЊC. Survival times of larvae more than doubled under aerated conditions. Adults survived Ͼ30 h of immersion in severely hypoxic water, substantially longer than reported for other tested tiger beetle species. Although riverine populations survive longer periods of immersion, dams cause habitats used by riverine populations of this species to be inundated for weeks at a time, far longer than larvae were able to survive under hypoxic or aerated conditions in the laboratory. Thus, alteration of ßooding regimes and subsequent larval habitat immersion is probably a major cause of the observed decline of riverine populations of C. hirticollis. Moreover, these data represent the Þrst report of signiÞcant physiological differences among populations of an insect species exposed to different frequencies of immersion and thus have both important experimental and evolutionary implications.
The larvae of the tiger beetle, Cicindela hirticollis Say, inhabit sandy shoreline areas that flood periodically. This species has declined over much of its range and at least one subspecies is near extinction, possibly as a result of human alteration of waterways. In addition to physiological tolerance for anoxia, the larvae have physical and behavioral adaptations to avoid drowning. We hypothesized that C. hirticollis larvae would exhibit behavioral responses to soil moisture change and flooding because, unlike most other tiger beetles, they frequently relocate their burrows. Our laboratory studies demonstrated that larvae select surface soil moisture levels of 7-50% saturation in which to dig new burrows. Within 96 h of immersion, most larvae abandon burrows and larvae do not form new burrows in darkness. Larvae may relocate when flooded, suggesting a previously undocumented mechanism for dispersal; however, dams often eliminate suitable habitat areas downstream, suggesting that this behavior may be detrimental in riverine populations. Because larvae move during daylight hours, they also are likely to suffer mortality from trampling due to human recreational activity.
Flooding exposes terrestrial organisms to severe hypoxia. Among the best- studied insects that are frequently exposed to flooding are tiger beetle (Coleoptera: Cicindelidae) larvae. In previous studies with a limited number of species, a correlation was found between habitat and hypoxia tolerance. In the current study, we examined hypoxia tolerance among third instars of six Cicindela species that vary in habitat association; we also tested adult survival of these species. We found that larvae of the different species survived an average of between 60 and 120 h of submersion in severely hypoxic water at 20°C, with larvae that occur in dry sand having somewhat lower survival times. However, among larvae, there was no correlation between survival times and habitat risk of flooding. We found surprisingly high survival times among adult tiger beetles with a range of 10 h to 46 h. Adult Cicindela formosa formosa Say that are associated with dry sand and are active in the spring and fall survived submersion for >40 h, longer than any previously reported adult terrestrial insect exposed to hypoxia at moderate environmental temperatures. The lengthy survival times of adult tiger beetles are likely a result of adaptations to immersion during periods of inactivity. Our study suggests that additional insect species and life stages should be examined for hypoxia tolerance regardless of perceived threat of immersion.
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