Joseph R. Bennett

Partitioning variation in ecological communities: do the numbers add up?

Summary 1. Statistical tests partitioning community variation into environmental and spatial components have been widely used to test ecological theories and explore the determinants of community structure for applied conservation questions. Despite the wide use of these tests, there is considerable debate about their relative effectiveness. 2. We used simulated communities to evaluate the most commonly employed tests that partition community variation: regression on distance matrices and canonical ordination using a third-order polynomial, principal components of neighbour matrices (PCNM) or Moran’s eigenvector maps (MEM) to model spatial components. Each test was evaluated under a variety of realistic sampling scenarios. 3. All tests failed to correctly model spatial and environmental components of variation, and in some cases produced biased estimates of the relative importance of components. Regression on distance matrices under-fit the spatial component, and ordination models consistently under-fit the environmental component. The PCNM and MEM approaches often produced inflated R2 statistics, apparently as a result of statistical artefacts involving selection of superfluous axes. This problem occurred regardless of the forward-selection technique used. 4. Both sample configuration and the underlying linear model used to analyse species–environment relationships also revealed strong potential to bias results. 5. Synthesis and applications. Several common applications of variation partitioning in ecology now appear inappropriate. These potentially include decisions for community conservation based on inferred relative strengths of niche and dispersal processes, inferred community responses to climate change, and numerous additional analyses that depend on precise results from multivariate variation-partitioning techniques. We clarify the appropriate uses of these analyses in research programmes, and outline potential steps to improve them.

Persistent millennial-scale shifts in moisture regimes in western Canada during the past six millennia.

Inferences of past climatic conditions from a sedimentary record from Big Lake, British Columbia, Canada, over the past 5,500 years show strong millennial-scale patterns, which oscillate between periods of wet and drier climatic conditions. Higher frequency decadal- to centennial-scale fluctuations also occur within the dominant millennial-scale patterns. These changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core. After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years. The correspondence of these shifts to millennial-scale variations in records of glacial expansion/recession and ice-rafting events in the Atlantic suggest that abrupt millennial-scale shifts are important to understanding climatic variability in North America during the mid- to late Holocene. Unfortunately, the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood. Similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions.

Biodiversity Risks from Fossil Fuel Extraction

The overlapping of biodiverse areas and fossil fuel reserves indicates high-risk regions. Despite a global political commitment to reduce biodiversity loss by 2010 through the 2002 Convention on Biological Diversity, declines are accelerating and threats are increasing (1). Major threats to biodiversity are habitat loss, invasion by exotic species and pathogens, and climate change, all principally driven by human activities. Although fossil fuel (FF) extraction has traditionally been seen as a temporary and spatially limited perturbation to ecosystems (2), even local or limited biodiversity loss can have large cascade effects on ecosystem function and productivity. We explore the overlap between regions of high marine and terrestrial biodiversity and FF reserves to identify regions at particular risk of ecosystem destruction and biodiversity loss from exposure to FF extraction.

Abundance, rarity and invasion debt among exotic species in a patchy ecosystem

Community assembly through species invasions is a long-term process, for which vital information regarding future trends can be contained in current patterns. Using comparative analyses of native and exotic plant assemblages from meadow patches on islands in British Columbia, Canada, we examined multiple lines of evidence for ‘invasion debt’, a latent expansion of exotic species populations. We show that: (1) short-dispersing species are underrepresented compared to their long-dispersing counterparts in exotic species only; (2) among species that are invasive elsewhere in North America, a greater proportion of long dispersers are common in the study area and a greater proportion of short dispersers are rare; and (3) time since arrival in the study region is positively related to number of occurrences in exotic species. In addition, we show that a suite of exotic species possesses the facility of rapid long-distance dispersal and ability to establish viable populations on even the most isolated and least disturbed patches. While some highly-dispersive exotic species can rapidly colonize new areas, short dispersers appear to exhibit invasion debt, with their potential distributions only being realized in the long term. Removing or even reducing populations of many rapid colonizers could be extremely difficult; however, for species exhibiting patterns most consistent with invasion debt, an opportunity exists for monitoring and removal to help reduce potential competition with native species.

Polar lessons learned: Long-term management based on shared threats in Arctic and Antarctic environments

The Arctic and Antarctic polar regions are subject to multiple environmental threats, arising from both local and ex-situ human activities. We review the major threats to polar ecosystems including the principal stressor, climate change, which interacts with and exacerbates other threats such as pollution, fisheries overexploitation, and the establishment and spread of invasive species. Given the lack of progress in reducing global atmospheric greenhouse-gas emissions, we suggest that managing the threats that interact synergistically with climate change, and that are potentially more tractable, is all the more important in the short to medium term for polar conservation. We show how evidence-based lessons learned from scientific research can be shared between the poles on topics such as contaminant mitigation, biosecurity protocols to reduce species invasions, and the regulation of fisheries and marine environments. Applying these trans-polar lessons in tandem with expansion of international cooperation could substantially improve environmental management in both the Arctic and Antarctic.

Biodiversity gains from efficient use of private sponsorship for flagship species conservation.

To address the global extinction crisis, both efficient use of existing conservation funding and new sources of funding are vital. Private sponsorship of charismatic ‘flagship’ species conservation represents an important source of new funding, but has been criticized as being inefficient. However, the ancillary benefits of privately sponsored flagship species conservation via actions benefiting other species have not been quantified, nor have the benefits of incorporating such sponsorship into objective prioritization protocols. Here, we use a comprehensive dataset of conservation actions for the 700 most threatened species in New Zealand to examine the potential biodiversity gains from national private flagship species sponsorship programmes. We find that private funding for flagship species can clearly result in additional species and phylogenetic diversity conserved, via conservation actions shared with other species. When private flagship species funding is incorporated into a prioritization protocol to preferentially sponsor shared actions, expected gains can be more than doubled. However, these gains are consistently smaller than expected gains in a hypothetical scenario where private funding could be optimally allocated among all threatened species. We recommend integrating private sponsorship of flagship species into objective prioritization protocols to sponsor efficient actions that maximize biodiversity gains, or wherever possible, encouraging private donations for broader biodiversity goals.

Optimizing taxonomic resolution and sampling effort to design cost-effective ecological models for environmental assessment

Predictive models relating ecological assemblages to environmental conditions are widely used in environmental impact assessment and biomonitoring. Such models are often parameterized using comprehensive ecological sampling and taxonomic identification efforts. Limited resources mean that expensive sampling and analytical procedures should be planned to maximize information gain and minimize unnecessary expense. However, there has been little consideration of cost-effectiveness in parameterizing predictive models using ecological assemblages and no explicit consideration of cost-effectiveness in balancing investment in the crucial aspects of sample size and taxonomic resolution. Using lacustrine diatom (Bacillariophyceae) assemblages from four large-scale (c. 77 000-1·3 million km2) data sets containing between 207 and 493 lakes, we address the following questions: (1) how does taxonomic resolution affect information content; (2) how does sample size affect information content for different taxonomic resolutions; and (3) what are the most cost-effective strategies for constructing environmental assessment models using diatom assemblages across a range of budgets? We use weighted averaging regression models for pH, phosphorus, salinity and lake depth and realistic data collection costs to examine the relationship between cost and model information content (R2 and root mean squared error of prediction). For diatom-based models, finer taxonomic resolutions almost always provide more cost-effective information content than collecting more samples, with (morpho)species being the most appropriate taxonomic resolution for nearly all budget scenarios. Information content exhibits an asymptotic relationship with sample size and budget, with greatest information gain during initial sample size increases, and little gain beyond c. 100 samples. Smaller sample sizes can also achieve surprising predictive power in some cases, suggesting low-cost regional models may be achievable. However, caution is necessary in such an approach, because spatial dependencies in predictions may be missed and analogues with predicted assemblages may be poor. Synthesis and applications. We demonstrate the utility of explicitly considering cost estimates to determine optimal sampling effort and taxonomic resolution for ecological assemblage models. For large, regional biomonitoring programmes, cost-effective sampling could save millions of dollars. Our framework for determining optimal trade-offs in ecological assemblage models is easily adaptable to other taxa and analytical techniques used in biomonitoring and environmental assessment.

Human Influence and Classical Biogeographic Predictors of Rare Species Occurrence

Biogeographic theory predicts that rare species occur more often in larger, less-isolated habitat patches and suggests that patch size and connectivity are positive predictors of patch quality for conservation. However, in areas substantially modified by humans, rare species may be relegated to the most isolated patches. We used data from plant surveys of 81 meadow patches in the Georgia Basin of Canada and the United States to show that presence of threatened and endangered plants was positively predicted for patches that were isolated on small islands surrounded by ocean and for patches that were isolated by surrounding forest. Neither patch size nor connectivity were positive predictors of rare species occurrence. Thus, in our study area, human influence, presumably due to disturbance or introduction of competitive non-native species, appears to have overwhelmed classical predictors of rare species distribution, such that greater patch isolation appeared to favor presence of rare species. We suggest conservation planners consider the potential advantages of protecting geographically isolated patches in human-modified landscapes because such patches may represent the only habitats in which rare species are likely to persist.

Spending limited resources on de-extinction could lead to net biodiversity loss

There is contentious debate surrounding the merits of de-extinction as a biodiversity conservation tool. Here, we use extant analogues to predict conservation actions for potential de-extinction candidate species from New Zealand and the Australian state of New South Wales, and use a prioritization protocol to predict the impacts of reintroducing and maintaining populations of these species on conservation of extant threatened species. Even using the optimistic assumptions that resurrection of species is externally sponsored, and that actions for resurrected species can share costs with extant analogue species, public funding for conservation of resurrected species would lead to fewer extant species that could be conserved, suggesting net biodiversity loss. If full costs of establishment and maintenance for resurrected species populations were publicly funded, there could be substantial sacrifices in extant species conservation. If conservation of resurrected species populations could be fully externally sponsored, there could be benefits to extant threatened species. However, such benefits would be outweighed by opportunity costs, assuming such discretionary money could directly fund conservation of extant species. Potential sacrifices in conservation of extant species should be a crucial consideration in deciding whether to invest in de-extinction or focus our efforts on extant species.

Prioritizing revived species: what are the conservation management implications of de‐extinction?

De-extinction technology that brings back extinct species, or variants on extinct species, is becoming a reality with significant implications for biodiversity conservation. If extinction could be reversed there are potential conservation benefits and costs that need to be carefully considered before such action is taken. Here, we use a conservation prioritization framework to identify and discuss some factors that would be important if de-extinction of species for release into the wild were a viable option within an overall conservation strategy. We particularly focus on how de-extinction could influence the choices that a management agency would make with regard to the risks and costs of actions, and how these choices influence other extant species that are managed in the same system. We suggest that a decision science approach will allow for choices that are critical to the implementation of a drastic conservation action, such as de-extinction, to be considered in a deliberate manner while identifying possible perverse consequences.