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opencc-zeroDec 2021View details →

Counterintuitive scaling between population abundance and local density: implications for modelling transmission of infectious diseases in bat populations

1. Models of host-pathogen interactions help to explain infection dynamics in wildlife populations and to predict and mitigate the risk of zoonotic spillover. Insights from models inherently depend on the way contacts between hosts are modelled, and crucially, how transmission scales with animal density. 2. Bats are important reservoirs of zoonotic disease and are among the most gregarious of all mammals. Their population structures can be highly heterogenous, underpinned by ecological processes across different scales, complicating assumptions regarding the nature of contacts and transmission. Although models commonly parameterise transmission using metrics of total abundance, whether this is an ecologically representative approximation of host-pathogen interactions is not routinely evaluated. 3. We collected a 13-month dataset of tree-roosting Pteropus spp. from 2,522 spatially referenced trees across eight roosts to empirically evaluate the relationship between total roost abundance and tree-level measures of abundance and density – the scale most likely to be relevant for virus transmission. We also evaluate whether roost features at different scales (roost-level, subplot-level, tree-level) are predictive of these local density dynamics. 4. Roost-level features were not representative of tree-level abundance (bats per tree) or tree-level density (bats per m2 or m3), with roost-level models explaining minimal variation in tree-level measures. Total roost abundance itself was either not a significant predictor (tree-level 3-D density) or only weakly predictive (tree-level abundance). 5. This indicates that basic measures, such as total abundance of bats in a roost, may not provide adequate approximations for population dynamics at scales relevant for transmission, and that alternative measures are needed to compare transmission potential between roosts. From the best candidate models, the strongest predictor of local population structure was tree density within roosts, where roosts with low tree density had a higher abundance but lower density of bats (more spacing between bats) per tree. 6. Together, these data highlight unpredictable and counterintuitive relationships between total abundance and local density. More nuanced modelling of transmission, spread and spillover from bats likely requires alternative approaches to integrating contact structure in host-pathogen models, rather than simply modifying the transmission function.

opencc-zeroMay 2022View details →

Estimating abundance in unmarked populations of Golden Eagle

1. Estimates of species abundance are of key importance in population and ecosystem level research but can be hard to obtain. Study designs using camera-traps are increasingly being used for large-scale monitoring of species that are elusive and/or occur naturally at low densities. 2. Golden eagle (Aquila chrysaetos) is one such species, and we investigate whether existing large-scale monitoring programs using baited camera-traps can be used to estimate the abundance of golden eagles, as an alternative to traditional labour-intensive searches for active territories and nest sites during the breeding period. 3. The camera-trap data allowed two measures of abundance to be estimated within each of four main study areas in mid and northern Norway; occupancy was measured as the probability of camera site use, and population size was measured as the number of eagle individuals using the camera sites within a study area. Spatial and temporal patterns in occupancy and population size were explored and evaluated against independent estimates of the breeding pair density in the study areas. 4. Annual estimates of golden eagle occupancy showed low precision, while estimates of population size were more precise in relation to both estimated and anticipated abundance fluctuations. Estimates of population size may therefore be suitable for monitoring within study area temporal abundance trends, while estimates of occupancy seem unsuitable for such in golden eagles. Across study areas, patterns in both average occupancy and average population density estimated from population size, were consistent with the spatial pattern in average breeding pair densities (r = 0.99, and r = 0.89 respectively). This suggests that camera-trap based estimates of occupancy and population density reflect territory density at large spatial scales. In conclusion, our results suggest that baited camera-traps can be a cost-effective strategy for monitoring the abundance of golden eagles.

opencc-zeroMay 2022View details →

Fruit-feeding butterfly populations respond to variation in adult food availability: evidence from longitudinal body mass and abundance data

The degree to which variation in adult food availability affects the population dynamics of a species depends on its position on the capital-income breeding continuum. The long-lived butterflies that feed on fruits as adults constitute an example of Lepidoptera with a high degree of income breeding. For three species of fruit-feeding butterflies in Uganda, we assessed the contribution of the income to breeding in the wild, and the consequences of variation in fruit availability for body mass and population dynamics. We interpreted body mass loss within individuals as well as younger individuals having higher body mass than older ones as evidence for the depletion of capital reserves. Despite large sample sizes, we were able to show only modest body mass loss in one species, indicating that large-bodied fruit-feeding butterflies are functionally income breeders in the wild. Butterfly body mass was sensitive to environmental factors, although the responses to fruit availability and weather parameters were dominated by interactive effects. In all three species, periods of higher availability of fruit were followed by periods of higher adult abundance three to five months later, fitting the egg-to-adult time. Our results suggest that adult food is rapidly used for reproduction so that body mass remains stable and population size responds to adult food availability. For these income breeding species, the frequent periods of low adult food availability may select for extended adult longevity for the purpose of postponing reproduction to the onset of more favorable conditions.

opencc-zeroDec 2021View details →

A novel SNP assay reveals increased genetic variability and abundance following translocations to a remnant Allegheny woodrat population

Background: Allegheny woodrats (Neotoma magister) are found in metapopulations distributed throughout the Interior Highlands and Appalachia. Historically these metapopulations persisted as relatively fluid networks, enabling gene flow between subpopulations and recolonization of formerly extirpated regions. However, over the past 45 years, Allegheny woodrat populations have experienced population declines throughout their range due to a combination of habitat destruction, declining hard mast availability, and roundworm parasitism. In an effort to initiate genetic rescue of a small, genetically depauperate subpopulation in New Jersey, woodrats were translocated from a genetically robust population in Pennsylvania (PA) in 2015, 2016, and 2017. Herein, we assess the efficacy of these translocations to restore genetic diversity within the recipient population. Results: We designed a novel 134 single nucleotide polymorphism panel, which was used to genotype the six woodrats translocated from PA and 82 individuals from the NJ population captured before and after the translocation events. These data indicated that a minimum of two translocated individuals successfully produced at least 16 offspring, who reproduced as well. Further, population-wide observed heterozygosity rose substantially following the first set of translocations, reached levels comparable to that of populations in Indiana and Ohio, and remained elevated throughout the following years. Abundance also increased during the monitoring period, suggesting Pennsylvania translocations initiated the genetic rescue of the New Jersey population. Conclusions: Our results indicate, encouragingly, that very small numbers of translocated individuals can successfully restore the genetic diversity of a threatened population. Our work also highlights the risks of managing very small populations, such as when translocated individuals have greater reproductive success relative to residents. Finally, we note that ongoing work with Allegheny woodrats may broadly shape our understanding of genetic rescue within metapopulations and across heterogeneous landscapes.

Figure 3 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 3. Distribution of biomass CPUA (kg km–2) A. kagoshimensis in 2011.

Figure 2 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 2. Sampling gear (hydroulic dredge).

Figure 6 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 6. Shell length–weight relationship of A. kagoshimensis by years.

Figure 1 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 1. Map showing the study areas and sampling stations in the Southwestern Black Sea

Figure 5 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 5. Change of per haul biomass by subarea and year.

Figure 4 in Population abundance and growth parameters of an exotic bivalve species, Anadara kagoshimensis, in the Southwestern Black Sea

Figure 4. Distribution of biomass A. kagoshimensis CPUA (kg km–2) in 2012.

opencc-by-4.0Jan 2015View details →

Figure 1 in Changes in abundance and community structure of the zooplankton population during the 2008 mucilage event in the northeastern Marmara Sea

Figure 1. Study area.

opencc-zeroJul 2023View details →

Variation among strains of Borrelia burgdorferi in host tissue abundance and lifetime transmission determine the population strain structure in nature

Pathogen life history theory assumes a positive relationship between pathogen load in host tissues and pathogen transmission. Empirical evidence for this relationship is surprisingly rare due to the difficulty of measuring transmission for many pathogens. The comparative method, where a common host is experimentally infected with a set of pathogen strains, is a powerful approach for investigating the relationships between pathogen load and transmission. The validity of such experimental estimates of strain-specific transmission is greatly enhanced if they can predict the pathogen population strain structure in nature. Borrelia burgdorferi is a multi-strain, tick-borne spirochete that causes Lyme disease in North America. This study used 11 field-collected strains of B. burgdorferi, a rodent host (Mus musculus, C3H/HeJ) and its tick vector (Ixodes scapularis) to determine the relationship between pathogen load in host tissues and lifetime host-to-tick transmission (HTT). Mice were experimentally infected via tick bite with 1 of 11 strains. Lifetime HTT was measured by infesting mice with I. scapularis larval ticks on 3 separate occasions. The prevalence and abundance of the strains in the mouse tissues and the ticks were determined by qPCR. We used published databases to obtain estimates of the frequencies of these strains in wild I. scapularis populations. Spirochete loads in ticks and lifetime HTT varied significantly among the 11 strains of B. burgdorferi. Strains with higher spirochete loads in the host tissues were more likely to infect feeding larvae, which molted into nymphs with a higher probability of B. burgdorferi infection (i.e., higher HTT). Our laboratory-based estimates of lifetime HTT were predictive of the frequencies of these strains in wild I. scapularis populations. For B. burgdorferi, the strains that establish high abundance in host tissues and that have high lifetime transmission are the strains that are most common in nature.

opencc-zeroAug 2023View details →

Abundance and population growth estimates for bare-nosed wombats

Wildlife managers often rely on population estimates, but estimates can be challenging to obtain for geographically widespread species. Spotlight surveys provide abundance data for many species and, when conducted over wide spatial scales, have the potential to provide population estimates of geographically widespread species. The bare-nosed wombat (Vombatus ursinus) has a broad geographic range and is subject to spotlight surveys. We used 19 years (2002–2020) of annual spotlight surveys to provide the first estimates of population abundance for two of the three extant bare-nosed wombat subspecies: V. u. ursinus on Flinders Island; and V. u. tasmaniensis on the Tasmanian mainland. Using distance sampling methods, we estimated annual rates of change and 2020 population sizes for both sub-species. Tasmanian mainland surveys included habitat data, which allowed us to also look for evidence of habitat associations for V. u. tasmaniensis. The average wombat density estimate was higher on Flinders Island (0.42 ha-1, 95% CrI = 0.25 – 0.79) than on the Tasmanian mainland (0.11 ha-1, CrI = 0.07 – 0.19) and both wombat subspecies increased over the 19-year survey period with an estimated annual growth rate of 2.90% (CrI = -1.7 – 7.3) on Flinders Island and 1.20% (CrI = -1.1 – 2.9) on mainland Tasmania. Habitat associations for V. u. tasmaniensis were weak, possibly owing to survey design; however, we detected regional variation in density for this subspecies. We estimated the population size of V. u. ursinus to be 71,826 (CrI = 43,913 – 136,761) on Flinders Island, which when combined with a previously published estimate of 2,599 (CI = 2,254 – 2,858) from Maria Island, where the subspecies was introduced, provides a total population estimate. We also estimated 840,665 (CrI = 531,104 – 1,201,547) V. u. tasmaniensis on mainland Tasmania. These estimates may be conservative, owing to individual heterogeneity in when wombats emerge from burrows. Although these two sub-species are not currently threatened, our population estimates provide an important reference when assessing their population status in the future, and demonstrate how spotlight surveys can be valuable to inform management of geographically widespread species.