Reynolds, D. J. | bioRxiv Science

bioRxiv2024

Ancient environmental DNA indicates limited human impact on marine biodiversity in pre-industrial Iceland

Human activities are affecting marine biodiversity globally by accelerating extinction rates, altering ecosystem conditions, and changing community structures. These changes can only be understood through establishing the ecosystem state prior to significant anthropogenic impact, and by disentangling the anthropogenic effect from natural climatic changes. Here, we reconstruct marine biodiversity in Iceland across three millennia (1315 BCE-1785 CE), encompassing periods of climatic fluctuation and human settlement, to explore the comparative effect of natural and anthropogenic forces on marine biodiversity. We performed 18S metabarcoding of ancient environmental DNA from two sediment cores collected from northern Icelandic shelf seas, integrating local climatic records, population estimates and zooarchaeological remains from published sources to estimate the influence of climatic and anthropogenic impacts. Against the backdrop of increasing human populations and marine exploitation, we observe no large-scale taxonomic shifts or anthropogenic biodiversity changes across the period. In contrast, we found a positive correlation between herring (Clupea harengus) detection rates and proxy-reconstructed sea surface temperature, suggesting a role for climate in shaping marine biodiversity. Overall, our data suggest that despite impacts on terrestrial ecosystems and the development of a substantial export fishery across the study period, Icelandic society may have had a limited effect on marine biodiversity.

ecology↗

bioRxiv2023

Characterization of human lightness discrimination thresholds for independent spectral variations

The lightness of an object is an intrinsic property that depends on its surface reflectance spectrum. The visual system estimates an objects lightness from the light reflected off its surface. The light reflected also depends on object extrinsic properties of the scene. For stable perception, the visual system needs to discount variations due to extrinsic properties. We characterize this perceptual stability for variation in two spectral properties of the scene: the reflectance spectra of background objects and the intensity of light sources. We use a two-alternative forced-choice task to measure human observers thresholds of discriminating computer-generated images of 3D scenes based on the lightness of a spherical target object in the scene. We measured how the discrimination thresholds changed as we varied the reflectance spectra of the objects and the intensity of the light sources in the scene, both individually and simultaneously. For small amounts of extrinsic variations, the thresholds of discrimination remained constant indicating that the thresholds were dominated by observers intrinsic representation of lightness. As extrinsic variation increased, it started affecting observers lightness judgment and the thresholds increased. We estimated that the effects of extrinsic variations were comparable to observers intrinsic variation in the representation of object lightness. Moreover, for simultaneous variation of these spectral properties, the increase in threshold square compared to no variation condition was a linear sum of the corresponding increase in threshold squares for the individual properties, indicating that the variation from these independent sources combines linearly.

animal behavior and cognition↗