Uncertainty in invasive alien species listing McGeoch, Melodie A.; Spear, Dian; Kleynhans, Elizabeth J. ...
Ecological applications,
04/2012, Letnik:
22, Številka:
3
Journal Article
Recenzirano
Lists of invasive alien species (IAS) are essential for preventing, controlling, and reporting on the state of biological invasions. However, these lists suffer from a range of errors, with serious ...consequences for their use in science, policy, and management. Here we (1) collated and classified errors in IAS listing using a taxonomy of uncertainty; and (2) estimated the size of these errors using data from a completed listing exercise, with the purpose of better understanding, communicating, and dealing with them. Ten errors were identified. Most result from a lack of knowledge or measurement error (epistemic uncertainty), although two were a result of context dependence and vagueness (linguistic uncertainty). Estimates of the size of the effects of these errors were substantial in a number of cases and unknown in others. Most errors, and those with the largest estimated effect, result in underestimates of IAS numbers. However, there are a number of errors where the size and direction of the effect remains poorly understood. The effect of differences in opinion between specialists is potentially large, particularly for data-poor taxa and regions, and does not have a clearly directional or consistent effect on the size and composition of IAS lists. Five tactics emerged as important for reducing uncertainty in IAS lists, and while uncertainty will never be removed entirely, these approaches will significantly improve the transparency, repeatability, and comparability of IAS lists. Understanding the errors and uncertainties that occur during the process of listing invasive species, as well as the potential size and nature of their effects on IAS lists, is key to improving the value of these lists for governments, management agencies, and conservationists. Such understanding is increasingly important given positive trends in biological invasion and the associated risks to biodiversity and biosecurity.
A central current debate in community ecology concerns the relative importance of deterministic versus stochastic processes underlying community structure. However, the concept of stochasticity ...presents several profound philosophical, theoretical and empirical challenges, which we address here. The philosophical argument that nothing in nature is truly stochastic can be met with the following operational concept of neutral stochasticity in community ecology: change in the composition of a community (i.e. community dynamics) is neutrally stochastic to the degree that individual demographic events – birth, death, immigration, emigration – which cause such changes occur at random with respect to species identities. Empirical methods for identifying the stochastic component of community dynamics or structure include null models and multivariate statistics on observational species-by-site data (with or without environmental or trait data), and experimental manipulations of 'stochastic' species colonization order or relative densities and frequencies of competing species. We identify the fundamental limitations of each method with respect to its ability to allow inferences about stochastic community processes. Critical future needs include greater precision in articulating the link between results and ecological inferences, a comprehensive theoretical assessment of the interpretation of statistical analyses of observational data, and experiments focusing on community size and on natural variation in species colonization order.
Invasive alien species (IAS) pose a significant threat to biodiversity. The Convention on Biological Diversity's 2010 Biodiversity Target, and the associated indicator for IAS, has stimulated ...globally coordinated efforts to quantify patterns in the extent of biological invasion, its impact on biodiversity and policy responses. Here, we report on the outcome of indicators of alien invasion at a global scale. Global. We developed four indicators in a pressure-state-response framework, i.e. number of documented IAS (pressure), trends in the impact of IAS on biodiversity (state) and trends in international agreements and national policy adoption relevant to reducing IAS threats to biodiversity (response). These measures were considered best suited to providing globally representative, standardized and sustainable indicators by 2010. We show that the number of documented IAS is a significant underestimate, because its value is negatively affected by country development status and positively by research effort and information availability. The Red List Index demonstrates that IAS pressure is driving declines in species diversity, with the overall impact apparently increasing. The policy response trend has nonetheless been positive for the last several decades, although only half of countries that are signatory to the Convention on Biological Diversity (CBD) have IAS-relevant national legislation. Although IAS pressure has apparently driven the policy response, this has clearly not been sufficient and/or adequately implemented to reduce biodiversity impact. For this indicator of threat to biodiversity, the 2010 Biodiversity Target has thus not been achieved. The results nonetheless provide clear direction for bridging the current divide between information available on IAS and that needed for policy and management for the prevention and control of IAS. It further highlights the need for measures to ensure that policy is effectively implemented, such that it translates into reduced IAS pressure and impact on biodiversity beyond 2010.
In the absence of migration, species persistence depends on adaption to a changing environment, but whether and how adaptation to global change is altered by community diversity is not understood. ...Community diversity may prevent, enhance or alter how species adapt to changing conditions by influencing population sizes, genetic diversity and/or the fitness landscape experienced by focal species. We tested the impact of community diversity on adaptation by performing a reciprocal transplant experiment on grasses that evolved for 14 years under ambient and elevated CO2, in communities of low or high species richness. Using biomass as a fitness proxy, we find evidence for local adaptation to elevated CO2, but only for plants assayed in a community of similar diversity to the one experienced during the period of selection. Our results indicate that the biological community shapes the very nature of the fitness landscape within which species evolve in response to elevated CO2.
The decline of many woodland caribou (Rangifer tarandus caribou) populations is thought to be linked with habitat disturbances resulting from industrial development, including timber harvesting and ...its network of haul roads. Defining a disturbance‐abundance relationship offers a tool to assess and potentially manage for the influence of disturbance on caribou abundance. Defining this relationship is challenged by limited historical land use and abundance data, the choice of a disturbance measure, and variability in the relationship between subpopulations and across core versus matrix habitat. For 12 subpopulations of woodland caribou within the southern mountain population, we linked longitudinal caribou abundance data with historical forestry disturbances simulated from forest harvest data. We compared disturbance measures estimating the proportion of forested area commercially harvested with even‐aged, regeneration treatments (cutblocks) and converted to roads for transporting timber within subpopulation‐specific core and matrix habitats as predictors of caribou abundance. Non‐linear mixed models provided evidence that disturbances in matrix habitats negatively influenced caribou abundance, with the effects in core habitat being variable between subpopulations. Of the disturbance types evaluated, the best predictors included roads buffered by 50 m (R50), cutblocks ≤80 years old, and the cumulation of cutblocks ≤80 years old plus roads buffered by 50 m. The top‐ranked model was composed of R50 present in core and in matrix habitats. This model predicted a 42% (95% CI = 33–51%) reduction in caribou abundance for every 1% increase in matrix R50 (holding core R50 constant). Given the lack of pre‐forestry abundance data, we failed to directly derive critical disturbance thresholds; however, our models could be used to estimate subpopulation‐specific habitat‐disturbance thresholds necessary to achieve abundance targets. We recommend that in addition to existing protections of core habitat, few if any new roads should be built in core habitat, and that timber harvest in matrix habitat should be designed to minimize the establishment of associated roads.
Using historical forestry disturbance data, a back‐casting approach, and hierarchical longitudinal caribou abundance data, we related caribou abundance with various measures of forestry disturbances (cutblocks and roads) calculated by caribou core or matrix habitat. Forestry roads within matrix habitat were strongly negatively related to caribou abundance and results provided evidence of subpopulation‐specific effects, highlighting the need to manage a range of disturbance thresholds for the recovery of this species.
Interspecific competition can strongly influence the evolutionary response of a species to a changing environment, impacting the chance that the species survives or goes extinct. Previous work has ...shown that when two species compete for a temporally shifting resource distribution, the species lagging behind the resource peak is the first to go extinct due to competitive exclusion. However, this work assumed symmetrically distributed resources and competition. Asymmetries can generate differences between species in population sizes, genetic variation and trait means. We show that asymmetric resource availability or competition can facilitate coexistence and even occasionally cause the leading species to go extinct first. Surprisingly, we also find cases where traits evolve in the opposite direction to the changing environment because of a ‘vacuum of competitive release’ created when the lagging species declines in number. Thus, the species exhibiting the slowest rate of trait evolution is not always the most likely to go extinct in a changing environment. Our results demonstrate that the extent to which species appear to be tracking environmental change and the extent to which they are preadapted to that change may not necessarily determine which species will be the winners and which will be the losers in a rapidly changing world.
Resource partitioning among mammalian savanna herbivores is thought to be predominantly driven by differences in body size. In general, large herbivore species utilize abundant low quality forage ...while small herbivores focus on scarcer high quality food items. However, in a natural system other factors such as digestive strategy, season and the presence of megaherbivores (body size > 1000 kg) are likely to complicate allometric predictions. Non-ruminants are probably better able to cope with abundant low quality food than ruminants of the same size causing a non-ruminant to act 'larger' than allometrically predicted. Also, the effect of alternating seasons with high and low food availability on diet choice and hence the competitive interactions between co-occurring herbivores is still poorly understood. Lastly, how megaherbivores deviate from allometric predictions (based on smaller species) is still not well quantified. In this study we examine resource partitioning among three ruminant and three non-ruminant grazers: impala, wildebeest, buffalo, warthog, zebra and white rhinoceros (megaherbivore) in the savanna of Hluhluwe iMfolozi Park, South Africa. We analysed habitat and diet overlap, specifically grass species (something not commonly investigated) and grass height eaten, in both the wet and the dry seasons. We found that habitat utilization differences among the species were generally small and did not vary between seasons. Diets within feeding patches overlapped during the wet season but highly diverged during the dry season. Body mass differences among species explained their dry season resource partitioning for all species except for comparisons with the megaherbivore (white rhino), while differences in digestive strategy were not related to niche overlap in either season. We conclude that savanna herbivores in this system coexist mostly through body size-driven resource partitioning in the dry-season, with the exception of the white rhino (megaherbivore).
Interspecific competition can strongly influence the evolutionary response of a species to a changing environment, impacting the chance that the species survives or goes extinct. Previous work has ...shown that when two species compete for a temporally shifting resource distribution, the species lagging behind the resource peak is the first to go extinct due to competitive exclusion. However, this work assumed symmetrically distributed resources and competition. Asymmetries can generate differences between species in population sizes, genetic variation and trait means. We show that asymmetric resource availability or competition can facilitate coexistence and even occasionally cause the leading species to go extinct first. Surprisingly, we also find cases where traits evolve in the opposite direction to the changing environment because of a 'vacuum of competitive release' created when the lagging species declines in number. Thus, the species exhibiting the slowest rate of trait evolution is not always the most likely to go extinct in a changing environment. Our results demonstrate that the extent to which species appear to be tracking environmental change and the extent to which they are preadapted to that change may not necessarily determine which species will be the winners and which will be the losers in a rapidly changing world.
Mycobacterium bovis infection in wildlife species occurs worldwide. However, few cases of M. bovis infection in captive elephants have been reported. We describe 2 incidental cases of bovine ...tuberculosis in free-ranging African elephants (Loxodonta africana) from a tuberculosis-endemic national park in South Africa and the epidemiologic implications of these infections.
We mapped and measured all of the Adansonia rubrostipa trees in 40 ha of dry deciduous forest in Kirindy Forest, Menabe, western Madagascar. Survey effort was split between three compartments which ...had been heavily logged or selectively logged for timber trees, not including A. rubrostipa, in the 1980s, or which remained unlogged. We recorded 304 trees ranging in stem diameter at breast height from 5 to 221 cm. Trees were most abundant and the majority of regeneration was recorded in the unlogged compartment. Regeneration was generally poor in the two logged compartments. We suggest that seed predation and poor seed dispersal contribute to a generally ageing population, and that the dense shrub cover resulting from disturbance during logging impedes seedling establishment.
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