Following the track: accuracy and reproducibility of predation assessment on artificial caterpillars

Experimental studies of biotic interactions in real field conditions are essential to understand the structure and functioning of ecological networks. The use of artificial caterpillars to mimic actual prey availability is generally seen as a standard approach to compare the activity and diversity of predators along environmental gradients. Yet, even with standardized material and procedures, biases may still affect data from multiple observers with different expertise. We used pictures of artificial caterpillars with or without various predation marks, in an online survey that was targeted for the participants of the project, to evaluate the reliability of predation marks identification made by non-scientists and by scientists with and without previous experience in predation mark identification. Pictures of artificial caterpillars displayed typical marks left by birds, mammals and arthropods, as well as non-predation marks (false positive). 357 respondents scanned 7140 pictures of these pictures. Self-declared scientists were more confident and accurate in their observations than non-scientists, but the differences in correct identifications among scientists and non-scientists were low. Self-declared scientists with previous experience were also more accurate than scientists without previous experience, while there were no differences in self-confidence among scientists with and without previous experience. Accuracy in predation mark identification did not differ among types of predators, but respondents were more keen to identify marks left by birds or mammals than arthropods. Our results have practical implications for the design of multi-observer projects relying on artificial caterpillars as a proxy to assess predation intensity, in particular in the context of citizen science.

MICROMORPHY OFFERS EFFECTIVE DEFENCE AGAINST PREDATION: INSIGHTS FROM THE COST-BENEFIT ANALYSES OF MICRO GASTROPOD PREDATION RECORD

Predation, an important driver of natural selection, is studied in the fossil record using quantifiable traces like drill holes produced by gastropods and repair scars produced after durophagous attacks. Despite the abundance of such records in molluscan prey, predation records of micromolluscs (<5mm) remained unexplored. Using a Miocene assemblage of microgastropods from the Quilon Limestone, India, we established the predatory-prey dynamics with the help of cost-benefit analyses. The overall predation intensity is low (DF = 0.06, RF= 0.04) and does not depend on the relative abundance of prey groups suggesting a non-random prey selection regardless of the encounter frequency. The predation is selective in terms of taxonomy, ornamentation, and size of the prey. The smallest size class has the lowest DF and RF supporting a negative size refugia. Higher IDF in larger size class and ornamented groups implies morphological defense resulting in higher failure. Microgastropods show a lower predation intensity than their regular-sized counterparts in a global comparison of coeval records. Results of the cost-benefit analyses explain this difference; the net energy gain from predatory drilling is found to increase monotonically with increasing prey size making the small prey less beneficial. Because the predators try to maximize net energy gain from a predatory attack, the microgastropod prey characterized by relatively low net energy yield is not preferred in the presence of larger prey. Micromorphy, therefore, appears a viable strategy for the prey group to be adopted as an evolutionary response against predation, especially in resource-limited conditions that fail to support large body size.

Multifunctionality of an Urbanized Coastal Marine Ecosystem

Coastal marine ecosystems provide numerous invaluable services and benefits to humankind. However, urbanization of coastal areas has homogenized and reduced the biodiversity of the surrounding marine environment and the sustainability of the multiple ecosystem services it provides. Studies have focused on single ecosystem functions despite human populations relying on several functions being delivered at once (known as multifunctionality). This study investigates five ecosystem functions (primary productivity, herbivory, predation, organic matter decomposition and carbon sequestration) and overall multifunctionality in four sites along a gradient of 16 environmental parameters. Ecosystem function varied significantly between sites that were farthest apart. In determining factors that drove ecosystem functioning, we found a positive relationship between coral cover and primary productivity but negative relationships between coral cover and levels of herbivory and predation intensity. Higher temperatures and greater concentrations of chlorophyll-a had a positive impact on predation and herbivory, respectively. Notably, we found a significant negative impact of total inorganic nitrogen and significant positive impact of total Kjeldahl nitrogen on carbon sequestration. Further, individual functions were compared with fish abundance (obtained from seawater eDNA), and benthic community composition (obtained from plate % coverage of autonomous reef monitoring structures). Increasing herbivorous fish abundance had a positive impact on Ulva mass loss. Overall, relative abundance of predatory, omnivorous and planktivorous fish exerted overriding influences on primary productivity and predation intensity, implying that fishing pressure and marine protected area status are important factors. Importantly, we found significant effects from environmental parameters indicating that reliably predicting the effects of future anthropogenic impacts will not be straightforward as multiple drivers are likely to have complex effects. Taken together, urbanized coastal ecosystems exhibit varying levels of multifunctionality depending on the extent of human impact, and the functional diversity of the benthic community present.

Prey–predator interaction suggests sacred groves are not functionally different from neighbouring used lands

Sacred groves (SG) of south India are either relics of primary or secondary forests or swamps, worshipped by the local communities, and distributed in the countrysides (CS) and forest landscapes of India. Studies suggest that SGs harbour a biodiversity different from that of adjoining CS and have a structural similarity to protected forests. Studies also suggest a negative effect of structural complexity of forests on predation. Considering these two expectations, we compared the predation of artificial caterpillars inside SGs and CSs with the hypothesis that predation will be less in SG than in CS. Examining the predation marks, we identified the likely predator and scored the intensity of predation. Bite marks of arthropods, birds, lizards and mammals were observed on caterpillars of both habitats. The predation rate and predation intensity were similar for overall predators and for each predator taxon in both habitats, despite the fact that mammal predation was mostly encountered in SGs. Because the proportion of predated caterpillars is not different between habitats and the intensity of predation is high in SGs, we conclude that SGs may not have a quality of the expected standard.

Low predation intensity on the stalked crinoid Democrinus sp. (Echinodermata) in Roatán, Honduras reveals deep water as likely predation refuge

Predation has been hypothesized to play a key role in the evolutionary and ecological history of crinoids. Whereas evidence of predation on crinoids in the form of injuries can be common, quantifying predation intensity, which is critical for properly evaluating such hypotheses, has proven challenging. Here, we used a longitudinal approach to quantify predation intensity on the extant, deep-water, stalked crinoid, Democrinus sp. The quantitative estimates are based on data collected from a manned submersible during expeditions conducted over a 3-yr span. These results indicate that this deep-water crinoid is subject to much lower predation intensity than are crinoids living in shallow water, consistent with (1) an inverse relationship between predation intensity and depth, and (2) the hypothesis that for stalked crinoids, which are unable to handle high predation intensity, deep water is a refugium.