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549 results for “population size”

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dryad40/100

Genetic evidence for widespread population size expansion in North American boreal birds prior to the Last Glacial Maximum

Pleistocene climate cycles are well known to have shaped contemporary species distributions and genetic diversity. Northward range expansions in response to deglaciation following the Last Glacial Maximum (LGM; ~21,000 years ago) have been surmised to lead to population size expansions in terrestrial taxa and changes in seasonal migratory behaviour. Recent findings, however, suggest that some northern temperate populations may have been more stable than expected through the LGM. We modelled the demographic history of twenty co-distributed boreal-breeding bird species of North America from full mitochondrial gene sets and species-specific molecular rates. We used these demographic reconstructions to test how species with different migratory strategies were affected by glacial cycles. Our results suggest that effective population sizes increased in response to deglaciation during the middle Wisconsin period (~45,000 years ago) whereas genetic diversity was maintained throughout the LGM despite shifts in geographic range. We conclude that earlier glacial cycles prior to the LGM have most strongly shaped contemporary genetic diversity in these high-latitude species. We did not find differences in historic population dynamics between species differing in migratory behaviour, contributing to growing evidence that major switches in migratory strategy during the Last Glacial Maximum are unnecessary to explain contemporary migratory patterns.

opencc-zeroDec 2022View details →

dryad40/100

Whole genome demographic models indicate divergent effective population size histories shape contemporary genetic diversity gradients in a montane bumble bee

Understanding historical range shifts and population size variation provides important context for interpreting contemporary genetic diversity. Methods to predict changes in species distributions and model changes in effective population size (Ne) using whole genomes make it feasible to examine how temporal dynamics influence diversity across populations. We investigate Ne variation and climate-associated range shifts to examine the origins of a previously observed latitudinal heterozygosity gradient in the bumble bee Bombus vancouverensis Cresson (Hymenoptera: Apidae: Bombus Latreille) in western North America. We analyze whole genomes from a latitude-elevation cline using sequentially Markovian coalescent models of Ne through time to test whether relatively low diversity in southern high-elevation populations is a result of long-term differences in Ne. We use Maxent models of the species range over the last 130,000 years to evaluate range shifts and stability. Ne fluctuates with climate across populations, but more genetically diverse northern populations have maintained greater Ne over the late Pleistocene and experienced larger expansions with climatically favorable time periods. Northern populations also experienced larger bottlenecks during the last glacial period which matched the loss of range area near these sites, however, bottlenecks were not sufficient to erode diversity maintained during periods of large Ne. A genome sampled from an island population indicated a severe postglacial bottleneck, indicating that large recent post-glacial declines are detectable if they have occurred. Genetic diversity was not related to niche stability or glacial-period bottleneck size. Instead, spatial expansions and increased connectivity during favorable climates likely maintain diversity in the north while restriction to high elevations maintains relatively low diversity despite greater stability in southern regions. Results suggest genetic diversity gradients reflect long-term differences in Ne dynamics and also emphasize the unique effects of isolation on insular habitats for bumble bees. Patterns are discussed in the context of conservation under climate change.

opencc-zeroJan 2023View details →

zenodo40/100

Supplementary material for Metabolic constraints on the body size scaling of extreme population densities

Data for the analysis of the paper entitled Metabolic constraints on the body size scaling of extreme population densities. Ecology letters. <a href="https://zenodo.org/api/files/a60c335d-e6ca-4bd9-a17f-fc98ca9703e2/air_sea_outputs_L4_nsw.txt?versionId=1416dceb-47d0-45b1-99a8-baa833df8f76">air_sea_outputs_L4_nsw.txt </a> This data set contains 8693 rows and 13 variables From colum 1 to 13 the following names apply: Julian- Day of the year (1rst January =1) day- Day number month- Month number year- Year number lat- Latitude lon- Longitude wind_speed_m_s- 1m wind speed in meters per second  presure_mB- Air pressure in milibars Temp_°C- Air temperature in degrees Celsius  Temp_algo- Other temperature Cloud_cover%- Percentage of cloud cover SST_°C- sea surface temperature in degree Celsius SW_Radiation_W_m2- Short wave radiation in Watts per square meter. <a href="https://zenodo.org/api/files/a60c335d-e6ca-4bd9-a17f-fc98ca9703e2/SurfaceTemperature_L4_Merged.csv?versionId=9738e9d6-53ed-49c4-ab0d-136b74ddb16e">SurfaceTemperature_L4_Merged.csv </a> This data set has 1064 rows and two columns Fechas_tempAll is the date of measurement formated as (Year-Month-Day Hour) e.g. 2013-05-20 09:00:00 TEMP_EC- Surface water Temperature in degree Celsius <a href="https://zenodo.org/record/7374166/files/Nutrients.csv?download=1">Nutrients.csv</a> The data set sas 445 rows and 8 Variables Sample.Date- Date when surface water sample was taken. NITRITE.µM, - Nitrite (NO2) concentration in micromolar NITRATE.NITRITE.µM"- Nitrate (NO3) concentration in micromolar AMMONIA.µM, - Ammonia (NH4) concentration in micromolar SILICATE.µM, - Silica (Si) concentration in micromolar PHOSPHATE.µM- - Posphate (PO4) concentration in micromolar FLAG- Quality flag (TRUE/FALSE).

opencc-by-4.0Feb 2023View details →

dryad40/100

Sex, body size, and winter weather explain migration strategies in a partial migrant population of American Kestrels (Falco sparverius)

Given increasing evidence that climate change affects the annual cycles of birds, it is important to understand the mechanisms underlying individual migration strategies and population-level patterns in partial migrants. In this study, we found that thermoregulation (body size and winter temperatures) was a key driver of American Kestrel (Falco sparverius) migration decisions. The annual proportion of migrants in the population, however, was not explained by winter weather and may be the result of differential survival. We measured stable hydrogen isotope values (δD) of talon tissues collected from 501 breeding and overwintering birds to distinguish migrant from resident kestrels in a partially migratory population of American Kestrels in southwestern Idaho in 2013–2021. We then evaluated drivers of migration decisions by assessing potential correlates of migration strategies, whether individuals switched migration strategies between years, and whether the proportion of migrants in the population changed over time or was correlated with winter weather. Male kestrels were 1.6 times more likely to migrate than females, and in colder than average winters, smaller birds of both sexes were more likely to migrate than larger birds. Only 27% of 26 recaptured individuals showed evidence of switching their migration strategies on an annual basis. There was no temporal trend in the proportion of migrants in the population, but proportions varied between years. Interestingly, there was no association between winter minimum temperature anomalies and annual migrant proportions in the population, suggesting that differential over-winter survival, or other stochastic processes, may play an important role in population composition. As winters continue to warm, fewer kestrels may migrate and more may remain resident on breeding grounds. However, it is unclear how changes in migration strategies might affect population-level patterns and resilience to climate change.

opencc-zeroApr 2023View details →

dryad40/100

National forest inventory data for a size-structured forest population model

In forest communities, light competition is a key process for community assembly. Species' differences in seedling and sapling tolerance to shade cast by overstory trees is thought to determine species composition at late-successional stages. Most forests are distant from these late-successional equilibria, impeding a formal evaluation of their potential species composition. To extrapolate competitive equilibria from short-term data, we therefore introduce the JAB model, a parsimonious dynamic model with interacting size-structured populations, which focuses on sapling demography including the tolerance to overstory competition. We apply the JAB model to a two-"species" system from temperate European forests, i.e. the shade-tolerant species Fagus sylvatica L. and the group of all other competing species. Using Bayesian calibration with prior information from external Slovakian national forest inventory (NFI) data, we fit the JAB model to short timeseries from the German NFI. We use the posterior estimates of demographic rates to extrapolate that F. sylvatica will be the predominant species in 94% of the competitive equilibria, despite only predominating in 24% of the initial states. We further simulate counterfactual equilibria with parameters switched between species to assess the role of different demographic processes for competitive equilibria. These simulations confirm the hypothesis that the higher shade-tolerance of F. sylvatica saplings is key for its long-term predominance. Our results highlight the importance of demographic differences in early life stages for tree species assembly in forest communities.

opencc-zeroJun 2023View details →

dryad40/100

Leveraging the strengths of citizen science and structured surveys to achieve scalable inference on population size

<ol> <li>Population size is a key metric for management and policy decisions, yet wildlife monitoring programs are often limited by the spatial and temporal scope of surveys. In these cases, citizen science data may provide complementary information at higher resolution and greater extent.</li> <li>We present a case study demonstrating how data from the eBird citizen science program can be combined with regional monitoring efforts by the U.S. Fish and Wildlife Service to produce high-resolution estimates of golden eagle abundance. We developed a model that uses aerial survey data from the western United States to calibrate high-resolution annual estimates of relative abundance from eBird. Using this model, we compared regional population size estimates based on the calibrated eBird information to those based on aerial survey data alone.</li> <li>Population size estimates based on the calibrated eBird information had strong correspondence to estimates from aerial survey data in two out of four regions, and population trajectories based on the two approaches showed high correlations.</li> <li>We demonstrate how the combination of citizen science data and targeted surveys can be used to (a) increase the spatial resolution of population size estimates, (b) extend the spatial extent of inference, and (c) predict population size beyond the temporal period of surveys. Findings based on this case study can be used to refine policy metrics used by the U.S. Fish and Wildlife Service and inform permitting regulations (e.g., mortality/harm associated with wind energy development).</li> <li> Policy implications. Our results demonstrate the ability of citizen science data to complement targeted monitoring programs and improve the efficacy of decision frameworks that require information on population size or trajectory. After validating citizen science data against survey-based benchmarks, agencies can harness strengths of citizen science data to supplement information needs and increase the resolution and extent of population size predictions.</li> </ol>

opencc-zeroSep 2023View details →

dryad40/100