Comparative Prey Spectra Analyses on the Endangered Aquatic Carnivorous Waterwheel Plant (Aldrovanda vesiculosa, Droseraceae) at Several Naturalized Microsites in the Czech Republic and Germany

Synopsis The critically endangered carnivorous waterwheel plant (Aldrovanda vesiculosa, Droseraceae) possesses underwater snap traps for capturing small aquatic animals, but knowledge on the exact prey species is limited. Such information would be essential for continuing ecological research, drawing conclusions regarding trapping efficiency and trap evolution, and eventually, for conservation. Therefore, we performed comparative trap size measurements and snapshot prey analyses at seven Czech and one German naturalized microsites on plants originating from at least two different populations. One Czech site was sampled twice during 2017. We recorded seven main prey taxonomic groups, that is, Cladocera, Copepoda, Ostracoda, Ephemeroptera, Nematocera, Hydrachnidia, and Pulmonata. In total, we recorded 43 different prey taxa in 445 prey-filled traps, containing in sum 461 prey items. With one exception, prey spectra did not correlate with site conditions (e.g. water depth) or trap size. Our data indicate that A. vesiculosa shows no prey specificity but catches opportunistically, independent of prey species, prey mobility mode (swimming or substrate-bound), and speed of movement. Even in cases where the prey size exceeded trap size, successful capture was accomplished by clamping the animal between the traps’ lobes. As we found a wide prey range that was attracted, it appears unlikely that the capture is enhanced by specialized chemical- or mimicry-based attraction mechanisms. However, for animals seeking shelter, a place to rest, or a substrate to graze on, A. vesiculosa may indirectly attract prey organisms in the vicinity, whereas other prey capture events (like that of comparably large notonectids) may also be purely coincidental.

Risky Pursuits: Martu Hunting and the Effects of Prey Mobility: Reply to Ugan and Simms

We recently demonstrated that prey size is not a reliable predictor of post-encounter return rates for resources Martu hunters regularly handle in Australia’s Western Desert (Bird et al. 2009). Ugan and Simms are skeptical of our calculations of these returns, especially in our inclusion of tracking as pursuit time. Here we review how these variables were recorded and calculated, update the analysis with more data, and clarify the importance of prey mobility and pursuit failures for understanding the contexts of hunting decisions and their archaeological implications.

On Prey Mobility, Prey Rank, and Foraging Goals

In their recent paper “In Pursuit of Mobile Prey,” Bird, Bliege-Bird, and Codding (2009) identify a negative relationship between body size and post-encounter returns among Martu prey in western Australia, attributing the phenomena to the greater mobility of large animals and associated risk of hunting failure. While this phenomenon has implications for archaeological applications of foraging models that assume body size and on-encounter returns are positively correlated, the Martu data may be less exceptional than they appear. Here we outline the reasons for our skepticism, point out areas in which we are in agreement, and build upon their findings by exploring the trade-offs between foraging to maximize efficiency and immediate returns and foraging for purposes other than immediate provisioning.

In Pursuit of Mobile Prey: Martu Hunting Strategies and Archaeofaunal Interpretation

By integrating foraging models developed in behavioral ecology with measures of variability in faunal remains, zooarchaeological studies have made important contributions toward understanding prehistoric resource use and the dynamic interactions between humans and their prey. However, where archaeological studies are unable to quantify the costs and benefits associated with prey acquisition, they often rely on proxy measures such as prey body size, assuming it to be positively correlated with return rate. To examine this hypothesis, we analyze the results of 1,347 adult foraging bouts and 649 focal follows of contemporary Martu foragers in Australia's Western Desert. The data show that prey mobility is highly correlated with prey body size and is inversely related to pursuit success—meaning that prey body size is often an inappropriate proxy measure of prey rank. This has broad implications for future studies that rely on taxonomic measures of prey abundance to examine prehistoric human ecology, including but not limited to economic intensification, socioeconomic complexity, resource sustainability, and overexploitation.