Predators impact prey by killing them for food. This is the popular conception. It is also the prevalent view in ecological and environmental sciences, in regards to theoretical models built to investigate general phenomenon such as biodiversity and in management models designed to e.g., investigate the effect of fishing or invasive species on e.g., marine and freshwater ecosystems. But we know prey don't passively sit around and get eaten; they display many means to detect and avoid predation. What we are learning is that these changes are far more extensive than avoiding nearby predators: prey change their behavioral characteristics, such as spending more time in refuges, moving slower for the entire day, or even growing larger protective spines. We are further learning that whereas such responses may save the prey, they can come at a very large cost to the prey and have large effects on ecosystems. Such effects caused by a predator by "scaring prey" (rather than eating them) are called non-consumptive effects (NCEs). We investigated this problem in the Lake Michigan food web. Zooplankton -- small crustaceans 1 to 6mm long -- are animals lowest in marine and freshwater food webs that serve as the major resource for the entire upper food web, including fish. The spiny water flea (SWF) is an invasive invertebrate that preys on zooplankton, and thus has been hypothesized to disrupt Great Lake's food webs and fisheries. We investigated whether non-consumptive effects may be at play. We had previous evidence that suggested Daphnia (a zooplankton prey) can perceive SWF scent in the water, and respond by swimming deeper in laboratory water columns. In the present work, we have extended our previous finding: at the higher end of SWF densities in the field, Daphnia are found on average 11 meters deeper. Pinning this finding down was not simply a matter of measuring Daphnia at low and high SWF densities, because there are many different factors that correlate with SWF densities. For example, SWF densities are higher later in the season, so perhaps Daphnia are just lower late in the season but not due to the SWF. Our statistical analysis allowed us to show that indeed Daphnia swim much lower in the day, but come up at night when the threat of SWF is lower. We further found that this effect extends to many other zooplankton, including various types of copepods (the major crustacean in ocean waters). We further found in laboratory experiments that copepod prey may respond so strongly to the scent of SWF that they reduce egg production, and may even die prematurely! Meanwhile, since SWF is an invasive species, and potential prey for fish, we investigated if SWF itself is evolving to its new environment. We found indeed that there is strong selection on its long conspicuous spine (a protective feature against fish), but that selection in opposite directions at different periods of the year essentially even out. Our results have implications for how managers view the effects of SWF in Lake Michigan, but also predators on prey in general. For example, at the heart of most ecological models is the need to represent how many prey predators kill as a function of prey density. Our work is showing that the type of response zooplankton display in response to predators dramatically alters this relationship, which can have a surprisingly large influence on model predictions. This work had a number of broader impacts. As described above, the research is uncovering a potentially general feature of food webs. Training included 1 post-doctoral associate in writing, data-analysis, and mentoring that will be applied at a faculty position secured during tenure on this project. It also supported 1 graduate student, and eight undergraduate students. Mentorship of undergraduate students included independent projects that included oral presentations and co-authorship on journal articles. Research was presented to both scientific and bro...
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