Complex rift geometries resulting from inheritance of pre-existing structures: Insights and regional implications from the Barmer Basin rift

Structural studies of the Barmer Basin in Rajasthan, northwest India, demonstrate the important effect that pre-existing faults can have on the geometries of evolving fault systems at both the outcrop and basin-scale. Outcrop exposures on opposing rift margins reveal two distinct, non-coaxial extensional events. On the eastern rift margin northwest–southeast extension was accommodated on southwest- and west-striking faults that form a complex, zig-zag fault network. On the western rift margin northeast–southwest extension was accommodated on northwest-striking faults that form classical extensional geometries. Combining these outcrop studies with subsurface interpretations demonstrates that northwest–southeast extension preceded northeast–southwest extension. Structures active during the early, previously unrecognised extensional event were variably incorporated into the evolving fault systems during the second. In the study area, an inherited rift-oblique fault transferred extension from the rift margin to a mid-rift fault, rather than linking rift margin fault systems directly. The resultant rift margin accommodation structure has important implications for early sediment routing and depocentre evolution, as well as wider reaching implications for the evolution of the rift basin and West Indian Rift System. The discovery of early rifting in the Barmer Basin supports that extension along the West Indian Rift System was long-lived, multi-event, and likely resulted from far-field plate reorganisations

Developing a frame of reference for fisheries management and conservation interventions

Effective implementation of management interventions is often limited by uncertainty, particularly in small-scale and developing-world fisheries. An effective intervention must have a measurable benefit, and evaluation of this benefit requires an understanding of the historical and socio-ecological context in which the intervention takes place. This context or ‘frame of reference’ should include the baseline status of the species of interest, as well as the most likely counterfactual (a projected scenario indicating what would have occurred in the absence of the intervention), given recent trends. Although counterfactuals are difficult to estimate and so are not widely specified in practice, an informative frame of reference can be developed even in data-poor circumstances. We demonstrate this using a case study of the Bangladesh hilsa (Tenualosa ilisha) fishery. We combine qualitative and some quantitative analyses of secondary datasets to explore ecological trends in the hilsa fishery, as well as patterns of social, economic, institutional, and physical change relevant to its management over the last ∼50 years. We compile all available information on the key parameters that determine hilsa abundance and distribution (movement, reproduction, growth, and mortality), as well as all available information on stock status. This information is used to produce a baseline and qualitative counterfactual which can be used to guide decision-making in this complex, data-poor fishery. A frame of reference provides a systematic way to break down potential drivers of change in a fishery, including their interactions, reducing the potential for unexpected management outcomes. Critical evaluation of contradictions and commonalities between a set of potential counterfactuals, as well as the reliability of sources, allows the identification of key areas of uncertainty and information needs. These can then be incorporated into fisheries management planning

Complex rift geometries resulting from inheritance of pre-existing structures: Insights and regional implications from the Barmer Basin rift

Structural studies of the Barmer Basin in Rajasthan, northwest India, demonstrate the important effect that pre-existing faults can have on the geometries of evolving fault systems at both the outcrop and basin-scale. Outcrop exposures on opposing rift margins reveal two distinct, non-coaxial extensional events. On the eastern rift margin northwest–southeast extension was accommodated on southwest- and west-striking faults that form a complex, zig-zag fault network. On the western rift margin northeast–southwest extension was accommodated on northwest-striking faults that form classical extensional geometries.Combining these outcrop studies with subsurface interpretations demonstrates that northwest–southeast extension preceded northeast–southwest extension. Structures active during the early, previously unrecognised extensional event were variably incorporated into the evolving fault systems during the second. In the study area, an inherited rift-oblique fault transferred extension from the rift margin to a mid-rift fault, rather than linking rift margin fault systems directly. The resultant rift margin accommodation structure has important implications for early sediment routing and depocentre evolution, as well as wider reaching implications for the evolution of the rift basin and West Indian Rift System. The discovery of early rifting in the Barmer Basin supports that extension along the West Indian Rift System was long-lived, multi-event, and likely resulted from far-field plate reorganisations

Cheaters allow cooperators to prosper

Cooperation based on the production of costly common goods is observed throughout nature. This is puzzling, as cooperation is vulnerable to exploitation by defectors which enjoy a fitness advantage by consuming the common good without contributing fairly. Depletion of the common good can lead to population collapse and the destruction of cooperation. However, population collapse implies small population size, which, in a structured population, is known to favor cooperation. This happens because small population size increases variability in cooperator frequency across different locations. Since individuals in cooperator-dominated locations (which are most likely cooperators) will grow more than those in defector-dominated locations (which are most likely defectors), cooperators can outgrow defectors globally despite defectors outgrowing cooperators in each location. This raises the possibility that defectors can lead to conditions that sometimes rescue cooperation from defector-induced destruction. We demonstrate multiple mechanisms through which this can occur, using an individual-based approach to model stochastic birth, death, migration, and mutation events. First, during defector-induced population collapse, defectors occasionally go extinct before cooperators by chance, which allows cooperators to grow. Second, empty locations, either preexisting or created by defector-induced population extinction, can favor cooperation because they allow cooperator but not defector migrants to grow. These factors lead to the counterintuitive result that the initial presence of defectors sometimes allows better survival of cooperation compared to when defectors are initially absent. Finally, we find that resource limitation, inducible by defectors, can select for mutations adaptive to resource limitation. When these mutations are initially present at low levels or continuously generated at a moderate rate, they can favor cooperation by further reducing local population size. We predict that in a structured population, small population sizes precipitated by defectors provide a "built-in" mechanism for the persistence of cooperation

Developing a frame of reference for fisheries management and conservation interventions

Effective implementation of management interventions is often limited by uncertainty, particularly in small-scale and developing-world fisheries. An effective intervention must have a measurable benefit, and evaluation of this benefit requires an understanding of the historical and socio-ecological context in which the intervention takes place. This context or ‘frame of reference’ should include the baseline status of the species of interest, as well as the most likely counterfactual (a projected scenario indicating what would have occurred in the absence of the intervention), given recent trends. Although counterfactuals are difficult to estimate and so are not widely specified in practice, an informative frame of reference can be developed even in data-poor circumstances. We demonstrate this using a case study of the Bangladesh hilsa (Tenualosa ilisha) fishery. We combine qualitative and some quantitative analyses of secondary datasets to explore ecological trends in the hilsa fishery, as well as patterns of social, economic, institutional, and physical change relevant to its management over the last ∼50 years. We compile all available information on the key parameters that determine hilsa abundance and distribution (movement, reproduction, growth, and mortality), as well as all available information on stock status. This information is used to produce a baseline and qualitative counterfactual which can be used to guide decision-making in this complex, data-poor fishery. A frame of reference provides a systematic way to break down potential drivers of change in a fishery, including their interactions, reducing the potential for unexpected management outcomes. Critical evaluation of contradictions and commonalities between a set of potential counterfactuals, as well as the reliability of sources, allows the identification of key areas of uncertainty and information needs. These can then be incorporated into fisheries management planning

Reversing declines in farmland birds: How much agri-environment provision is needed at farm and landscape scales?

Funder: Royal Society for the Protection of BirdsAgri‐environment schemes (AES) are the primary policy mechanism for addressing farmland biodiversity declines across Europe. Despite previous studies on the impacts of AES on biodiversity, there is little empirical evidence on the scale of provision required to reverse declines. Across three regions of lowland England with contrasting farm systems (arable, pastoral, mixed), we estimated avian population growth rates (PGRs) on farmland with high AES provision (‘higher‐tier’: average bird‐friendly option cover = 7.4%), low AES provision (‘lower‐tier’: 2.3%) and no bird‐friendly AES (‘no AES’). Ten‐year PGRs were derived for 24 species and three multi‐species groups comprising farmland‐associated species (‘farmland birds’), species of conservation concern (‘priority birds’) and species restricted to farmland (‘specialist birds’). We used PGRs to simulate the proportion of the regional farmland landscape that would have to be assigned to higher‐ and lower‐tier agreements to stabilise or increase populations. In the arable and pastoral regions, 13/23 and 13/22 species, respectively, had more positive PGRs under higher‐tier AES than on no AES farmland (none had more negative PGRs), compared to 4/22 (positive) and 1/22 (negative) in the mixed region. Only two to four species per region exhibited more positive PGRs under lower‐tier AES compared to no AES farmland. Multi‐species PGRs in the arable and pastoral regions increased from no AES (strong decline), to lower‐tier (decline or stability) to higher‐tier (moderate or strong increase). There was no overall AES effect in the mixed region. To increase regional farmland bird populations by 10% over 10 years, 47% and 26% of the farmed landscape would need to be devoted to higher‐tier agreements in arable and pastoral landscapes respectively. This falls to 34% and 17% when higher‐tier is targeted at localities supporting higher abundances of target species, and to 29% and 10% when 30% of the farmed landscape is also devoted to lower‐tier. Priority and specialist birds require higher provision levels. Policy implications. Where farmland bird recovery is an AES objective, farms should prioritise higher‐tier agreement delivery over lower‐tier. Farmland bird responses to AES provision are likely to vary regionally, but careful targeting will reduce the amount needed in the landscape

Regional differences in thermoregulation between two European butterfly communities

Publication status: PublishedAbstract Understanding how different organisms cope with changing temperatures is vital for predicting future species' distributions and highlighting those at risk from climate change. As ectotherms, butterflies are sensitive to temperature changes, but the factors affecting butterfly thermoregulation are not fully understood. We investigated which factors influence thermoregulatory ability in a subset of the Mediterranean butterfly community. We measured adult thoracic temperature and environmental temperature (787 butterflies; 23 species) and compared buffering ability (defined as the ability to maintain a consistent body temperature across a range of air temperatures) and buffering mechanisms to previously published results from Great Britain. Finally, we tested whether thermoregulatory ability could explain species' demographic trends in Catalonia. The sampled sites in each region differ climatically, with higher temperatures and solar radiation but lower wind speeds in the Catalan sites. Both butterfly communities show nonlinear responses to temperature, suggesting a change in behaviour from heat‐seeking to heat avoidance at approximately 22°C. However, the communities differ in the use of buffering mechanisms, with British populations depending more on microclimates for thermoregulation compared to Catalan populations. Contrary to the results from British populations, we did not find a relationship between region‐wide demographic trends and butterfly thermoregulation, which may be due to the interplay between thermoregulation and the habitat changes occurring in each region. Thus, although Catalan butterfly populations seem to be able to thermoregulate successfully at present, evidence of heat avoidance suggests this situation may change in the future. </jats:p