Biology subjects

Dytham, C.

Publications and source records attributed to Dytham, C..

2 recordsLinked to original sources

bioRxiv2023

Estimating the distribution of reed Phragmites australis in Britain demonstrates challenges of remotely sensing rare land cover types at large spatial scales

Reed Phragmites australis is important for biodiversity, for ecosystem services, and as a resource for humans. Already one of the mostly widely distributed wetland plants globally, reed has recently expanded outside of its native range, modifying ecosystems. However, like most wetland plant communities, reedbed has rarely been mapped at large geographical scales, restricting the information available to ecologists and resource managers. Using Sentinel-2 data and machine learning in open-source software, we produce the first remotely-sensed reedbed map of Britain. A random forest was trained on 79.2 ha of reedbed and 2,719.2 ha of non-reedbed land cover, using free online imagery. Accuracy was high within the training area (AUC > 0.998); however, field validation accuracy was much lower (AUC = 0.671), with many false positives (commission error of 93.4%). A similar workflow carried out in Google Earth Engine, using nearly an order of magnitude more images, gave a lower commission error but a disproportionately higher omission error. Due to the classification error, our map is more useful for a non-spatial estimate of the overall reedbed extent in Britain, rather than for the spatial location of reedbeds in Britain. Using the known commission and omission error, we estimate that in 2015 - 2017 c. 7800 ha of Britain was reedbed. Our study highlights the issues that present enduring barriers to accurate land cover classification at large spatial scales, perhaps suggesting fruitful areas for technological innovation. Even with a big data approach and even if technological issues are resolved, ecological factors such as confusion land cover types and geographical variation in temporal reflectance function will probably continue to impose upper limits on the size of area for which land cover can be classified accurately, and therefore on the utility of remote sensing to resource managers.

ecology↗

bioRxiv2021

Social and physical environment independently affect oviposition decisions in Drosophila melanogaster

In response to environmental stimuli, including variation in the presence of conspecifics, animals show highly plastic responses in behavioural and physiological traits influencing reproduction. These responses have been extensively documented in males, but equivalent study of females is so far lacking. We expect females to be highly responsive to environmental variation, with significant impacts on fitness given females direct impact on offspring number, size, and developmental conditions. Using Drosophila melanogaster as a model, we manipulate (a) exposure to conspecific females, expected to influence their expectation of number of potential mates and larval density for their own offspring, and (b) test how prior consexual population density interacts with the spatial distribution of potential oviposition sites, with females expected to prefer clustered food resources that can support a larger number of eggs and larvae. After exposure to competition, females were slower to start copulating and reduced their copulation duration - the opposite effect to that observed in males previously exposed to rivals. There was a parallel and perhaps related effect on egg production, with females previously housed in groups laying fewer eggs than those that were housed in solitude. The spatial distribution of resources also influenced oviposition behaviour: females clearly preferred aggregated patches of substrate, being more likely to lay, and laying on more of the available patches, in the clustered environment. However, we found no significant interaction between prior housing conditions and resource patchiness, indicating that females did not perceive the value of different resource distributions differently when they were expecting either high or low levels of larval competition. While exposure to consexual competition influences copulatory behaviours, it is the distribution of oviposition resources that has a greater impact on oviposition decisions.

animal behavior and cognition↗