UCL University College London Eprints
UCL Eprints collects the work of UCL researchers and makes it freely available over the web, helping the worldwide scholarly community to discover UCL research. Institutional repositories like UCL Eprints complement the traditional academic publishing and scholarly communications processes. They raise the visibility of research and help to maximise its impact. UCL researchers are encouraged to deposit a copy of each journal article, conference paper, working paper, and any other research output, in the UCL Eprints at the earliest opportunity, ensuring that their research reaches as wide an audience as possible.
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Propagule pressure as a driver of establishment success in deliberately introduced exotic species: Fact or artefact? - Blackburn, TM; Prowse, TAA; Lockwood, JL; Cassey, P
A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously...
The performance of the global protected area system in capturing vertebrate geographic ranges - Cantú-Salazar, L; Orme, CDL; Rasmussen, PC; Blackburn, TM; Gaston, KJ
Given the heavy reliance placed on and investment in protected areas for biological conservation, there has been much debate as to how effective these are in representing biodiversity features within their boundaries. The majority of studies addressing this issue have been conducted on a regional or national basis, precluding a broad picture of patterns of representation at the species level. We present a global assessment of the representation of the terrestrial geographic ranges of complete taxonomic groups: all known extant amphibians, birds and mammals (20,736 species) within the current global system of protected areas. We conclude that it is necessary...
Maximizing the success of assisted colonizations - Chauvenet, ALM; Ewen, JG; Armstrong, DP; Blackburn, TM; Pettorelli, N
Climate change is causing spatio-temporal shifts in environmental conditions, and species that are not able to track suitable environments may face increased risks of extinction. Assisted colonization, a form of translocation, has been proposed as a tool to help species survive the impacts of climate change. Unfortunately, translocations generally have a low success rate, a well-documented fact that is not considered in most of the recent literature on assisted colonization. One of the main impediments to translocation success is inadequate planning. In this review, we argue that by using well-known analytical tools such as species distribution models and population dynamics...
What determines the impact of alien birds and mammals in Europe? - Kumschick, S; Bacher, S; Blackburn, TM
An often-cited reason for studying the process of invasion by alien species is that the understanding sought can be used to mitigate the impacts of the invaders. Here, we present an analysis of the correlates of local impacts of established alien bird and mammal species in Europe, using a recently described metric to quantify impact. Large-bodied, habitat generalist bird and mammal species that are widespread in their native range, have the greatest impacts in their alien European ranges, supporting our hypothesis that surrogates for the breadth and the amount of resources a species uses are good indicators of its impact....
Horizon scanning for invasive alien species with the potential to threaten biodiversity in Great Britain. - Roy, HE; Peyton, J; Aldridge, DC; Bantock, T; Blackburn, TM; Britton, R; Clark, P; Cook, E; Dehnen-Schmutz, K; Dines, T; Dobson, M; Edwards, F; Harrower, C; Harvey, MC; Minchin, D; Noble, DG; Parrott, D; Pocock, MJ; Preston, CD; Roy, S; Salisbury, A; Schönrogge, K; Sewell, J; Shaw, RH; Stebbing, P; Stewart, AJ; Walker, KJ
Invasive alien species (IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment....
A unified classification of alien species based on the magnitude of their environmental impacts. - Blackburn, TM; Essl, F; Evans, T; Hulme, PE; Jeschke, JM; Kühn, I; Kumschick, S; Marková, Z; Mrugała, A; Nentwig, W; Pergl, J; Pyšek, P; Rabitsch, W; Ricciardi, A; Richardson, DM; Sendek, A; Vilà, M; Wilson, JR; Winter, M; Genovesi, P; Bacher, S
Species moved by human activities beyond the limits of their native geographic ranges into areas in which they do not naturally occur (termed aliens) can cause a broad range of significant changes to recipient ecosystems; however, their impacts vary greatly across species and the ecosystems into which they are introduced. There is therefore a critical need for a standardised method to evaluate, compare, and eventually predict the magnitudes of these different impacts. Here, we propose a straightforward system for classifying alien species according to the magnitude of their environmental impacts, based on the mechanisms of impact used to code species...
Defining the impact of non-native species. - Jeschke, JM; Bacher, S; Blackburn, TM; Dick, JT; Essl, F; Evans, T; Gaertner, M; Hulme, PE; Kühn, I; Mrugała, A; Pergl, J; Pyšek, P; Rabitsch, W; Ricciardi, A; Richardson, DM; Sendek, A; Vilà, M; Winter, M; Kumschick, S
Non-native species cause changes in the ecosystems to which they are introduced. These changes, or some of them, are usually termed impacts; they can be manifold and potentially damaging to ecosystems and biodiversity. However, the impacts of most non-native species are poorly understood, and a synthesis of available information is being hindered because authors often do not clearly define impact. We argue that explicitly defining the impact of non-native species will promote progress toward a better understanding of the implications of changes to biodiversity and ecosystems caused by non-native species; help disentangle which aspects of scientific debates about non-native species...
Climatic predictors of temperature performance curve parameters in ectotherms imply complex responses to climate change. - Clusella-Trullas, S; Blackburn, TM; Chown, SL
Determining organismal responses to climate change is one of biology's greatest challenges. Recent forecasts for future climates emphasize altered temperature variation and precipitation, but most studies of animals have largely focused on forecasting the outcome of changes in mean temperature. Theory suggests that extreme thermal variation and precipitation will influence species performance and hence affect their response to changes in climate. Using an information-theoretic approach, we show that in squamate ectotherms (mostly lizards and snakes), two fitness-influencing components of performance, the critical thermal maximum and the thermal optimum, are more closely related to temperature variation and to precipitation, respectively, than...
Insect rate-temperature relationships: environmental variation and the metabolic theory of ecology. - Irlich, UM; Terblanche, JS; Blackburn, TM; Chown, SL
Much of the recent discussion concerning the form and underlying mechanistic basis of metabolic rate-temperature and development rate-temperature relationships has been precipitated by the development of the metabolic theory of ecology (MTE). Empirical tests of the theory's fundamental equation are an essential component of establishing its validity. Here, we test the temperature component of the fundamental equation of the MTE as it applies to metabolic rate and development rate, using insects as model organisms. Specifically, we test (i) whether mean activation energies, E, approximate the 0.65 eV value proposed by the proponents of the MTE and whether the range of...
Some methodological issues in macroecology. - Blackburn, TM; Gaston, KJ
Recent years have seen the emergence of "macroecology" as a distinct research program in biology. It is concerned with geographical scale patterns in assemblage structure and, as such, of necessity relies heavily on approaches that are nonexperimental and that depend on the availability of reliable information for large numbers of species. This gives rise to a particular set of analytical issues that need to be addressed when conducting studies of macroecological patterns. In this article, we draw attention to nine such issues that we consider to be of particular importance. Our aim is to aid the development of what we...
Basal metabolic rate of birds is associated with habitat temperature and precipitation, not primary productivity. - White, CR; Blackburn, TM; Martin, GR; Butler, PJ
A classic example of ecophysiological adaptation is the observation that animals from hot arid environments have lower basal metabolic rates (BMRs, ml O2min-1) than those from non-arid (luxuriant) ones. However, the term 'arid' conceals within it a multitude of characteristics including extreme ambient temperatures (Ta, degrees C) and low annual net primary productivities (NPPs, gCm-2), both of which have been shown to correlate with BMR. To assess the relationship between environmental characteristics and metabolic rate in birds, we collated BMR measurements for 92 populations representing 90 wild-caught species and examined the relationships between BMR and NPP, Ta, annual temperature range...
Global patterns of introduction effort and establishment success in birds. - Cassey, P; Blackburn, TM; Sol, D; Duncan, RP; Lockwood, JL
Theory suggests that introduction effort (propagule size or number) should be a key determinant of establishment success for exotic species. Unfortunately, however, propagule pressure is not recorded for most introductions. Studies must therefore either use proxies whose efficacy must be largely assumed, or ignore effort altogether. The results of such studies will be flawed if effort is not distributed at random with respect to other characteristics that are predicted to influence success. We use global data for more than 600 introduction events for birds to show that introduction effort is both the strongest correlate of introduction success, and correlated with...
A comparison of random draw and locally neutral models for the avifauna of an English woodland. - Dolman, AM; Blackburn, TM
Explanations for patterns observed in the structure of local assemblages are frequently sought with reference to interactions between species, and between species and their local environment. However, analyses of null models, where non-interactive local communities are assembled from regional species pools, have demonstrated that much of the structure of local assemblages remains in simulated assemblages where local interactions have been excluded. Here we compare the ability of two null models to reproduce the breeding bird community of Eastern Wood, a 16-hectare woodland in England, UK. A random draw model, in which there is complete annual replacement of the community by...
Determinants of establishment success in introduced birds. - Blackburn, TM; Duncan, RP
A major component of human-induced global change is the deliberate or accidental translocation of species from their native ranges to alien environments, where they may cause substantial environmental and economic damage. Thus we need to understand why some introductions succeed while others fail. Successful introductions tend to be concentrated in certain regions, especially islands and the temperate zone, suggesting that species-rich mainland and tropical locations are harder to invade because of greater biotic resistance. However, this pattern could also reflect variation in the suitability of the abiotic environment at introduction locations for the species introduced, coupled with known confounding effects...
Metapopulation dynamics, abundance, and distribution in a microecosystem - Gonzalez, A; Lawton, JH; Gilbert, FS; Blackburn, TM; Evans-Freke, I
The experimental fragmentation of landscapes of a natural ecosystem resulted in declines in the abundance and distribution of most species in the multispecies animal community inhabiting the landscapes and the extinction of many species. These declines caused the deterioration of the positive interspecific relation between local population abundance and distributional extent in this community. However, when patches were connected by habitat corridors, an immigration "rescue effect" arrested declines in both abundance and distribution and maintained the observed positive relation between them. These results demonstrate the importance of metapopulation dynamics and landscape connectivity for the persistence of populations in fragmented landscapes.
Animal body size distributions: patterns, mechanisms and implications. - Blackburn, TM; Gaston, KJ
Documenting the shape of the frequency distribution of species body sizes for an animal taxon appears at first sight a straightforward task. However, a variety of patterns has been reported, and a consensus is only now being reached through an understanding of how potential biases may affect observed shapes of distributions. A new body of evidence suggests that, at large scales, size distributions are right-skewed, even on logarithmic axes. If body size distributions can be described with certainty, this will allow assessment of the mechanisms proposed to generate them, and will be an important step towards understanding the structure and...
Animal body size distributions change as more species are described. - Blackburn, TM; Gaston, KJ
Frequency distributions of body size have been reported in the literature for a range of animal higher taxa. However, the reported shapes of these distributions may be biased by species missing from them, specifically by currently undiscovered species. There is a body of evidence that the small-bodied species in a taxon are described later, on average, than the large-bodied. From this, we predict that the means of animal body size frequency distributions should decrease through time, and the skewnesses of the distributions increase. These predictions are shown to be true for body size distributions for five different higher taxa of...
Parasite prevalence and host sample size. - Gregory, RD; Blackburn, TM
Parasite prevalence is a summary statistic familiar to biologists. However, that there is an interspecific relationship between prevalence and sample size (the number of host individuals examined for parasites) is not widely appreciated. In this article, Richard Gregory and Tim Blackburn present some examples of this negative relationship, explain the mechanisms that underlie this pattern and discuss the potential problems this association might create for biological studies.
A population model for predicting the successful establishment of introduced bird species. - Cassey, P; Prowse, TA; Blackburn, TM
One of the strongest generalities in invasion biology is the positive relationship between probability of establishment and the numbers of individuals introduced. Nevertheless, a number of significant questions remain regarding: (1) the relative importance of different processes during introduction (e.g., demographic, environmental, and genetic stochasticity, and Allee effects); (2) the relative effects of propagule pressure (e.g., number of introductions, size of introductions, and lag between introductions); and (3) different life history characteristics of the species themselves. Here, we adopt an individual-based simulation modeling approach to explore a range of such details in the relationship between establishment success and numbers of...
Long-distance dispersal maximizes evolutionary potential during rapid geographic range expansion. - Berthouly-Salazar, C; Hui, C; Blackburn, TM; Gaboriaud, C; van Rensburg, BJ; van Vuuren, BJ; Le Roux, JJ
Conventional wisdom predicts that sequential founder events will cause genetic diversity to erode in species with expanding geographic ranges, limiting evolutionary potential at the range margin. Here, we show that invasive European starlings (Sturnus vulgaris) in South Africa preserve genetic diversity during range expansion, possibly as a result of frequent long-distance dispersal events. We further show that unfavourable environmental conditions trigger enhanced dispersal, as indicated by signatures of selection detected across the expanding range. This brings genetic variation to the expansion front, counterbalancing the cumulative effects of sequential founding events and optimizing standing genetic diversity and thus evolutionary potential at...