A pinboard by
Fraser Combe

Papers associated with climate change and it's influence on small mammal populations

Climatw change is know to impact population demographics but the degree to which intrinsic factors such as density dependence synergistically relate to these extrinsic factors are relatively unknown. So here is a collection of papers I have collected on the topic


Lateglacial to Late Holocene palaeoclimatic and palaeoenvironmental reconstruction of El Mirador cave (Sierra de Atapuerca, Burgos, Spain) using the small-mammal assemblages

Abstract: El Mirador is a cave in the Sierra de Atapuerca (northern Iberian Peninsula) that contains 27 archaeological layers from the Lateglacial to the Late Holocene. A total of 4436 small-mammal remains have been analysed from these layers, and 19 taxa have been identified (three insectivores, seven chiropters and nine rodents). The palaeoenvironmental reconstruction based on a small-mammal analysis suggests that the entire sequence is dominated by a woodland landscape. Our climatic analysis characterises the climate in terms of an evolution from a cool and arid period in the Pleistocene layers (16,000 to 14,000 cal yr BP), probably related to Heinrich Event 1, to humid conditions and temperatures similar to nowadays in the Holocene layers in general. In MIR23 and MIR22 (7300 to 6800 cal yr BP) we detect an increase in temperature to levels above current values and an important decrease in rainfall. These climatic characteristics could be related to the end of the African Humid Period. Moreover, a short, slightly cooler event is registered in MIR11 (ca. 6300 to 5900 cal yr BP), coinciding with a change in the economic pattern in El Mirador. The results obtained on the basis of small-mammal studies are compared with multiproxy terrestrial data (pollen, charcoal, phytoliths, geochemistry, large mammals) and the Greenland ice-core record, as well as various other core records closer to the coasts of the Iberian Peninsula (MD95-2042, MD99-2331, MD95-2043 and SMP02-3). These comparisons show the agreement of the palaeoenvironmental and palaeoclimatic results with all the previous multiproxy and core-record data.

Pub.: 17 Jan '17, Pinned: 12 Sep '17

Environmental correlates of the Late Quaternary regional extinctions of large and small Palaearctic mammals

Abstract: Most studies of mammal extinctions during the Pleistocene–Holocene transition explore the relative effects of climate change vs human impacts on these extinctions, but the relative importance of the different environmental factors involved remains poorly understood. Moreover, these studies are strongly biased towards megafauna, which may have been more influenced by human hunting than species of small body size. We examined the potential environmental causes of Pleistocene–Holocene mammal extinctions by linking regional environmental characteristics with the regional extinction rates of large and small mammals in 14 Palaearctic regions. We found that regional extinction rates were larger for megafauna, but extinction patterns across regions were similar for both size groups, emphasizing the importance of environmental change as an extinction factor as opposed to hunting. Still, the bias towards megafauna extinctions was larger in southern Europe and smaller in central Eurasia. The loss of suitable habitats, low macroclimatic heterogeneity within regions and an increase in precipitation were identified as the strongest predictors of regional extinction rates. Suitable habitats for many species of the Last Glacial fauna were grassland and desert, but not tundra or forest. The low-extinction regions identified in central Eurasia are characterized by the continuous presence of grasslands and deserts until the present. In contrast, forest expansion associated with an increase in precipitation and temperature was likely the main factor causing habitat loss in the high-extinction regions. The shift of grassland into tundra also contributed to the loss of suitable habitats in northern Eurasia. Habitat loss was more strongly related to the extinctions of megafauna than of small mammals. Ungulate species with low tolerance to deep snow were more likely to go regionally extinct. Thus, the increase in precipitation at the Pleistocene–Holocene transition may have also directly contributed to the extinctions by creating deep snow cover which decreases forage availability in winter.

Pub.: 01 May '17, Pinned: 12 Sep '17

Climatic conditions produce contrasting influences on demographic traits in a long distance Arctic migrant.

Abstract: The manner in which patterns of variation and interactions among demographic rates contribute to population growth rate (λ) are key to understanding how animal populations will respond to changing climatic conditions. Migratory species are likely to be particularly sensitive to climatic conditions as they experience a range of different environments throughout their annual cycle. However, few studies have provided fully integrated demographic analyses of migratory populations in response to changing climatic conditions. Here, we employed integrated population models (IPM) to demonstrate that the environmental conditions experienced during a short, but critical period, play a central role in the demography of a long-distance migrant, the light-bellied Brent goose (Branta bernicla hrota). Female survival was positively associated with June North Atlantic Oscillation (NAO) values, whereas male survival was not. In contrast, breeding productivity was negatively associated with June NAO, suggesting a trade-off between female survival and reproductive success. Both adult female and adult male survival showed low temporal variation, whereas there was high temporal variation in recruitment and breeding productivity. In addition, while annual population growth was positively correlated with annual breeding productivity a sensitivity analysis revealed that population growth was most sensitive to changes in adult survival. Our results demonstrate that the environmental conditions experienced during a relatively short-time window at the start of the breeding season play a critical role in shaping the demography of a long-distant Arctic migrant. Crucially, different demographic rates responded in opposing directions to climatic variation, emphasizing the need for integrated analysis of multiple demographic traits when understanding population dynamics. This article is protected by copyright. All rights reserved.

Pub.: 16 Dec '16, Pinned: 12 Sep '17

Characterising demographic contributions to observed population change in a declining migrant bird

Abstract: Populations of Afro-Palearctic migrant birds have shown severe declines in recent decades. To identify the causes of these declines, accurate measures of both demographic rates (seasonal productivity, apparent survival, immigration) and environmental parameters will allow conservation and research actions to be targeted effectively. We used detailed observations of marked breeding birds from a ‘stronghold’ population of whinchats Saxicola rubetra in England (stable against the declining European trend) to reveal both on-site and external mechanisms that contribute to population change. From field data, a population model was developed based on demographic rates from 2011 to 2014. Observed population trends were compared to the predicted population trends to assess model-accuracy and the influence of outside factors, such as immigration. The sensitivity of the projected population growth rate to relative change in each demographic rate was also explored. Against expectations of high productivity, we identified low seasonal breeding success due to nocturnal predation and low apparent first-year survival, which led to a projected population growth rate (λ) of 0.818, indicating a declining trend. However, this trend was not reflected in the census counts, suggesting that high immigration was probably responsible for buffering against this decline. Elasticity analysis indicated λ was most sensitive to changes in adult survival but with covariance between demographic rates accounted for, most temporal variation in λ was due to variation in productivity. Our study demonstrates that high quality breeding habitat can buffer against population decline but high immigration and low productivity will expose even such stronghold populations to potential decline or abandonment if either factor is unsustainable. First-year survival also appeared low, however this result is potentially confounded by high natal dispersal. First-year survival and/or dispersal remains a significant knowledge gap that potentially undermines local solutions aimed at counteracting low productivity.

Pub.: 25 Jul '17, Pinned: 12 Sep '17

Climate-driven vital rates do not always mean climate-driven population.

Abstract: Current climatic changes have increased the need to forecast population responses to climate variability. A common approach to address this question is through models that project current population state using the functional relationship between demographic rates and climatic variables. We argue that this approach can lead to erroneous conclusions when interpopulation dispersal is not considered. We found that immigration can release the population from climate-driven trajectories even when local vital rates are climate dependent. We illustrated this using individual-based data on a trans-equatorial migratory seabird, the Scopoli's shearwater Calonectris diomedea, in which the variation of vital rates has been associated with large-scale climatic indices. We compared the population annual growth rate λi , estimated using local climate-driven parameters with ρi , a population growth rate directly estimated from individual information and that accounts for immigration. While λi varied as a function of climatic variables, reflecting the climate-dependent parameters, ρi did not, indicating that dispersal decouples the relationship between population growth and climate variables from that between climatic variables and vital rates. Our results suggest caution when assessing demographic effects of climatic variability especially in open populations for very mobile organisms such as fish, marine mammals, bats, or birds. When a population model cannot be validated or it is not detailed enough, ignoring immigration might lead to misleading climate-driven projections.

Pub.: 10 Jun '16, Pinned: 12 Sep '17

Integrated population modeling reveals the impact of climate on the survival of juvenile emperor penguins.

Abstract: Early-life demographic traits are poorly known, impeding our understanding of population processes and sensitivity to climate change. Survival of immature individuals is a critical component of population dynamics and recruitment in particular. However, obtaining reliable estimates of juvenile survival (i.e., from independence to first year) remains challenging, as immatures are often difficult to observe and to monitor individually in the field. This is particularly acute for seabirds, in which juveniles stay at sea and remain undetectable for several years. In this work, we developed a Bayesian integrated population model to estimate the juvenile survival of emperor penguins (Aptenodytes forsteri), and other demographic parameters including adult survival and fecundity of the species. Using this statistical method, we simultaneously analyzed capture-recapture data of adults, the annual number of breeding females, and the number of fledglings of emperor penguins collected at Dumont d'Urville, Antarctica, for the period 1971-1998. We also assessed how climate covariates known to affect the species foraging habitats and prey (southern annular mode (SAM), sea-ice concentration (SIC)) affect juvenile survival. Our analyses revealed that there was a strong evidence for the positive effect of SAM during the rearing period (SAMR) on juvenile survival. Our findings suggest that this large-scale climate index affects juvenile emperor penguins body condition and survival through its influence on wind patterns, fast ice extent, and distance to open water. Estimating the influence of environmental covariates on juvenile survival is of major importance to understand the impacts of climate variability and change on the population dynamics of emperor penguins and seabirds in general, and to make robust predictions on the impact of climate change on marine predators. This article is protected by copyright. All rights reserved.

Pub.: 23 Oct '16, Pinned: 12 Sep '17

Dampening of population cycles in voles affects small mammal community structure, decreases diversity, and increases prevalence of a zoonotic disease

Abstract: Long-term decline and depression of density in cyclic small rodents is a recent widespread phenomenon. These observed changes at the population level might have cascading effects at the ecosystem level. Here, we assessed relationships between changing boreal landscapes and biodiversity changes of small mammal communities. We also inferred potential effects of observed community changes for increased transmission risk of Puumala virus (PUUV) spread, causing the zoonotic disease nephropatica epidemica in humans. Analyses were based on long-term (1971–2013) monitoring data of shrews and voles representing 58 time series in northern Sweden. We calculated richness, diversity, and evenness at alpha, beta, and gamma level, partitioned beta diversity into turnover (species replacement) and nestedness (species addition/removal), used similarity percentages (SIMPER) analysis to assess community structure, and calculated the cumulated number of PUUV-infected bank voles and average PUUV prevalence (percentage of infected bank voles) per vole cycle. Alpha, beta, and gamma richness and diversity of voles, but not shrews, showed long-term trends that varied spatially. The observed patterns were associated with an increase in community contribution of bank vole (Myodes glareolus), a decrease of gray-sided vole (M. rufocanus) and field vole (Microtus agrestis) and a hump-shaped variation in contribution of common shrew (Sorex araneus). Long-term biodiversity changes were largely related to changes in forest landscape structure. Number of PUUV-infected bank voles in spring was negatively related to beta and gamma diversity, and positively related to turnover of shrews (replaced by voles) and to community contribution of bank voles. The latter was also positively related to average PUUV prevalence in spring. We showed that long-term changes in the boreal landscape contributed to explain the decrease in biodiversity and the change in structure of small mammal communities. In addition, our results suggest decrease in small mammal diversity to have knock-on effects on dynamics of infectious diseases among small mammals with potential implications for disease transmission to humans.

Pub.: 09 Jun '17, Pinned: 12 Sep '17

Are whooping cranes destined for extinction? Climate change imperils recruitment and population growth

Abstract: Identifying climatic drivers of an animal population's vital rates and locating where they operate steers conservation efforts to optimize species recovery. The population growth of endangered whooping cranes (Grus americana) hinges on juvenile recruitment. Therefore, we identify climatic drivers (solar activity [sunspots] and weather) of whooping crane recruitment throughout the species’ life cycle (breeding, migration, wintering). Our method uses a repeated cross-validated absolute shrinkage and selection operator approach to identify drivers of recruitment. We model effects of climate change on those drivers to predict whooping crane population growth given alternative scenarios of climate change and solar activity. Years with fewer sunspots indicated greater recruitment. Increased precipitation during autumn migration signified less recruitment. On the breeding grounds, fewer days below freezing during winter and more precipitation during breeding suggested less recruitment. We predicted whooping crane recruitment and population growth may fall below long-term averages during all solar cycles when atmospheric CO2 concentration increases, as expected, to 500 ppm by 2050. Species recovery during a typical solar cycle with 500 ppm may require eight times longer than conditions without climate change and the chance of population decline increases to 31%. Although this whooping crane population is growing and may appear secure, long-term threats imposed by climate change and increased solar activity may jeopardize its persistence. Weather on the breeding grounds likely affects recruitment through hydrological processes and predation risk, whereas precipitation during autumn migration may influence juvenile mortality. Mitigating threats or abating climate change should occur within ≈30 years or this wild population of whooping cranes may begin declining.

Pub.: 21 Mar '17, Pinned: 12 Sep '17

Evolutionary responses to a changing climate: Implications for reindeer population viability

Abstract: If we want to understand how climate change affects long-lived organisms, we must know how individuals allocate resources between current reproduction and survival. This trade-off is affected by expected environmental conditions, but the extent to which density independent (DI) and density dependent (DD) processes interact in shaping individual life histories is less clear. Female reindeer (or caribou: Rangifer tarandus) are a monotocous large herbivore with a circumpolar distribution. Individuals that experience unpredictable and potentially harsh winters typically adopt risk averse strategies where they allocate more resources to building own body reserves during summer and less to reproduction. Such a strategy implies that the females do not reproduce or that they produce fewer or smaller offspring. A risk averse strategy thus results in females with large autumn body reserves, which is known to increase their survival probabilities if the coming winter is harsh. In contrast, females experiencing predictable winters may adopt a more risk prone strategy in which they allocate more resources to reproduction as they do not need as many resources to buffer potentially adverse winter conditions. This study uses a seasonal state-dependent model showing that DD and DI processes interact to affect the evolution of reproductive strategies and population dynamics for reindeer. The model was run across a wide range of different winter climatic scenarios: One set of simulations where the average and variability of the environment was manipulated and one set where the frequency of good and poor winters increased. Both reproductive allocation and population dynamics of reindeer were affected by a combination of DI and DD processes even though they were confounded (harsh climates resulted in lowered density). Individual strategies responded, in line with a risk sensitive reproductive allocation, to climatic conditions and in a similar fashion across the two climatic manipulations.

Pub.: 20 Jun '17, Pinned: 12 Sep '17

The thermal niche of Neotropical nectar-feeding bats: Its evolution and application to predict responses to global warming

Abstract: The thermal niche of a species is one of the main determinants of its ecology and biogeography. In this study, we determined the thermal niche of 23 species of Neotropical nectar-feeding bats of the subfamily Glossophaginae (Chiroptera, Phyllostomidae). We calculated their thermal niches using temperature data obtained from collection records, by generating a distribution curve of the maximum and minimum temperatures per locality, and using the inflection points of the temperature distributions to estimate the species optimal (STZ) and suboptimal (SRZ) zones of the thermal niche. Additionally, by mapping the values of the STZ and SRZ on a phylogeny of the group, we generated a hypothesis of the evolution of the thermal niches of this clade of nectar-feeding bats. Finally, we used the characteristics of their thermal niches to predict the responses of these organisms to climate change. We found a large variation in the width and limits of the thermal niches of nectar-feeding bats. Additionally, while the upper limits of the thermal niches varied little among species, their lower limits differ wildly. The ancestral reconstruction of the thermal niche indicated that this group of Neotropical bats evolved under cooler temperatures. The two clades inside the Glossophaginae differ in the evolution of their thermal niches, with most members of the clade Choeronycterines evolving “colder” thermal niches, while the majority of the species in the clade Glossophagines evolving “warmer” thermal niches. By comparing thermal niches with climate change models, we found that all species could be affected by an increase of 1°C in temperature at the end of this century. This suggests that even nocturnal species could suffer important physiological costs from global warming. Our study highlights the value of scientific collections to obtain ecologically significant physiological data for a large number of species.

Pub.: 21 Jul '17, Pinned: 12 Sep '17