Benjamin G. Freeman results 20
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Pacific Northwest birds have shifted their abundances upslope in response to 30 years of warming temperaturesNARA Subscribed
Mountain species are predicted to respond to warming temperatures by moving to higher elevations that remain relatively cool. Species can track warming by shifting their entire distributions upwards (the “escalator to extinction” hypothesis) or by increasing in abundance in the upper portion of their elevational range while maintaining stable elevational limits (the “upslope lean” hypothesis). Alternatively, mountain species m...
Recent Abundance Changes at Species' Range Limits in the North and Central American AvifaunasNARA Subscribed
Aim Species are often expected to track climate change via changes in their abundances and distributions. This climate tracking hypothesis generates the prediction that warming temperatures should cause species to show population increases at their poleward range limits and population decreases at their equatorward range limits. We tested these predictions for 516 species of North and Central American birds. Location North and...
Interspecific competition shapes bird species' distributions along tropical precipitation gradientsNARA Subscribed
The hypothesis that species' ranges are limited by interspecific competition has motivated decades of debate, but a general answer remains elusive. Here we test this hypothesis for lowland tropical birds by examining species' precipitation niche breadths. We focus on precipitation because it—not temperature—is the dominant climate variable that shapes the biota of the lowland tropics. We used 3.6 million fine‐scale citizen sci...
Disentangling the historical routes to community assembly in the global epicentre of biodiversityNARA Subscribed
Aim The exceptional turnover in biota with elevation and number of species coexisting at any elevation makes tropical mountains hotspots of biodiversity. However, understanding the historical processes through which species arising in geographical isolation (i.e. allopatry) assemble along the same mountain slope (i.e. sympatry) remains a major challenge. Multiple models have been proposed including (1) the sorting of already e...
Host phylogeny and elevation predict infection by avian haemosporidians in a diverse New Guinean bird communityNARA Subscribed
Aim The biotic interactions hypothesis predicts that interactions between species are stronger at lower elevations compared to higher elevations. We tested whether this prediction is met by examining elevational patterns in avian haemosporidian infections in New Guinean birds. Location YUS Conservation Area, Papua New Guinea. Taxon Birds and haemosporidia. Methods We collected blood samples from 2268 individuals of 66 bird spe...
Prolonging survival in good health is a fundamental societal goal. However, the leading determinants of disability-free survival in healthy older people have not been well established. Data from ASPREE, a bi-national placebo-controlled trial of aspirin with 4.7 years median follow-up, was analysed. At enrolment, participants were healthy and without prior cardiovascular events, dementia or persistent physical disability. Disab...
Responsible agriculture must adapt to the wetland character of mid‐latitude peatlandsNARA Subscribed
Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yr −1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Red...
Global maps of soil temperatureNARA Subscribed
Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1‐km 2 r...
Functional traits offer a rich quantitative framework for developing and testing theories in evolutionary biology, ecology and ecosystem science. However, the potential of functional traits to drive theoretical advances and refine models of global change can only be fully realised when species‐level information is complete. Here we present the AVONET dataset containing comprehensive functional trait data for all birds, includi...
The latitudinal gradient in rates of evolution for bird beaks, a species interaction traitNARA Subscribed
Where is evolution fastest? The biotic interactions hypothesis proposes that greater species richness creates more ecological opportunity, driving faster evolution at low latitudes, whereas the ‘empty niches’ hypothesis proposes that ecological opportunity is greater where diversity is low, spurring faster evolution at high latitudes. We tested these contrasting predictions by analysing rates of beak evolution for a global dat...
Montane species track rising temperatures better in the tropics than in the temperate zoneNARA Subscribed
Many species are responding to global warming by shifting their distributions upslope to higher elevations, but the observed rates of shifts vary considerably among studies. Here, we test the hypothesis that this variation is in part explained by latitude, with tropical species being particularly responsive to warming temperatures. We analyze two independent empirical datasets—shifts in species’ elevational ranges, and changes...
Lower elevation animal species do not tend to be better competitors than their higher elevation relativesNARA Subscribed
Aim What factors set species' range edges? One general hypothesis, often attributed to Darwin and MacArthur, is that interspecific competition prevents species from inhabiting the warmest portions along geographic gradients (i.e., low latitudes or low elevations). A prediction arising from this Darwin–MacArthur hypothesis is that lower elevation species are better competitors than related higher elevation species. An alternati...
Expanding, shifting and shrinking: The impact of global warming on species’ elevational distributionsNARA Subscribed
Aim Species are responding to climate warming by shifting their distributions toward historically cooler regions, but the degree to which expansions at cool range limits are balanced by contractions at warm limits is unknown. We synthesized published data documenting shifts at species’ warm versus cool range limits along elevational gradients to (a) test classic ecological theory that predicts temperature more directly influen...
Aim Since Darwin, ecologists have assumed that species tend to be abundant in the centre of their geographic distributions and rare at their range edges. We test two predictions of this abundant centre hypothesis: (a) that species are common in the centre of their range and rare at the edges and (b) that empirical distributions along environmental gradients are well described by symmetric bell‐shaped curves. Location A reef‐to...
Little evidence for Bergmann's rule body size clines in passerines along tropical elevational gradientsNARA Subscribed
Aim To test whether intra‐ and interspecific patterns in body mass along elevational gradients follow Bergmann's rule for a subset of tropical montane passerines. Location Tropical elevational gradients in New Guinea, Borneo, Peru and Costa Rica. Methods I used linear regressions to assess intraspecific patterns in body mass along elevational gradients in common New Guinean passerines (2697 mist‐netted individuals of 21 specie...
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