Relative Predation Risk Research Articles

Diel variation in predator abundance, predation risk and prey distribution in shallow-water estuarine habitats

Predation by visual predators is often affected by light conditions and may therefore exhibit strong diel variation. The dominant predators on grass shrimp, Palaemonetes pugio, are finfish predators that are thought to locate their prey by visual cues. We examined the response of grass shrimp to diel variation in predation risk in the nearshore shallow waters of the Chesapeake Bay. We used diel shoreline seines to assess the relative abundance of predators. We assessed the relative risk of predation with shrimp tethered at refuge (30 cm) and nonrefuge (60 cm) depths. To measure grass shrimp response to predation risk, we used dipnets to monitor habitat use. Four predominantly visual predators dominated the shoreline seine catches, Fundulus heteroclitus, Micropogonias undulatus, Morone americana and Morone saxatilis. Total predator abundance had a diel component, with dramatic nighttime decreases in total abundance, whereas guild composition and relative abundance remained unchanged. Relative predation risk for tethered shrimp exhibited significant time by habitat interaction. During the day, depth negatively affected survivorship of tethered shrimp while at night overall survivorship increased and there was no effect of depth. Shrimp habitats use reflected diel predation risks. Abundances in the near shore were highest during the day with decreased abundances at night. Together, the seine and tethering data highlight the importance for a refuge (e.g., shallow water) from predation during the daytime and a relaxation of predation pressure at night.

A MULTISCALE BEHAVIORAL APPROACH TO UNDERSTANDING THE MOVEMENTS OF WOODLAND CARIBOU

We assessed the response of woodland caribou (Rangifer tarandus caribou) to land-cover type, predation risk, energetic costs of movement, and patch configuration at multiple spatial scales. We applied a nonlinear model to frequent locations collected with Global Positioning System (GPS) collars to identify discontinuities in the scales of movement by caribou found in forested and alpine (above tree line) habitats. We differentiated intra- from interpatch movements and identified collections of patches (multiple-patch scale) where caribou concentrated intrapatch movements. On average, intra- and interpatch movements were 450.7 and 1268.8 m, respectively, and multiple-patch movements occurred over an area of 182 ha. Intrapatch movements were highly correlated, indicative of a strong relationship between behavior and place. Caribou in the forest selected patches of Pine terrace, whereas caribou in the alpine selected patches of Alpine-little vegetative cover. Predation risk was not a factor influencing movements of caribou at the intrapatch scale. Selection of cover types was more variable during interpatch movements. At that scale, caribou selected patches of Pine terrace, Lakes/rivers, Alpine-little vegetative cover, and Alpine-grass. The routes selected by caribou had lower energetic costs relative to surrounding terrain, and during some winters, caribou were subjected to higher levels of predation risk during those movements. At the multiple-patch scale, selection was more specific and encompassed patches of Alpine-little vegetative cover, Alpine-grass, and Pine terrace. Predation risk was relatively unimportant at the multi-patch scale, but animals that moved from forested to alpine habitats reduced their relative risk of predation. Patch configuration was a poor predictor of those areas where caribou concentrated intrapatch movements. There was some evidence of caribou selecting patches of Pine terrace within a matrix of Wetlands and Pine–black spruce/black spruce patches. Caribou in the alpine avoided patches of Alpine-little vegetative cover adjacent to forest types. Our results indicate that forest managers should maintain widely distributed patches of Pine terrace and implement silvicultural regimes that do not stimulate predator populations across areas used for interpatch movements.

The Dilemma of the Selfish Herd: The Search for a Realistic Movement Rule

The selfish herd hypothesis predicts that aggregations form because individuals move toward one another to minimize their own predation risk. The “dilemma of the selfish herd” is that movement rules that are easy for individuals to follow, fail to produce true aggregations, while rules that produce aggregations require individual behavior so complex that one may doubt most animals can follow them. If natural selection at the individual level is responsible for herding behavior, a solution to the dilemma must exist. Using computer simulations, we examined four different movement rules. Relative predation risk was different for all four movement rules (p<0.05). We defined three criteria for measuring the quality of a movement rule. A good movement rule should (a) be statistically likely to benefit an individual that follows it, (b) be something we can imagine most animals are capable of following, and (c) result in a centrally compact flock. The local crowded horizon rule, which allowed individuals to take the positions of many flock-mates into account, but decreased the influence of flock-mates with distance, best satisfied these criteria. The local crowded horizon rule was very sensitive to the animal's perceptive ability. Therefore, the animal's ability to detect its neighbors is an important factor in the dynamics of group formation.

Do artificial nests reveal relative nest predation risk for real nests?

Present knowledge of the effects of nest predation on spatial distribution, habitat selection and community structure of birds is to a large extent based on results from experiments with artificial nests. Although nest predation risk is likely to differ between artificial and real nests, most previous studies of nest predation using artificial nests have been lacking a proper control. We investigated whether predation rates on artificial nests predicted those on real nests by simultaneously comparing the fate of real and artificial nests (containing quail Coturnix coturnix and plasticine eggs) in 92 territories of the northern wheatear Oenanthe oenanthe in 1996. We also investigated whether risk for artificial nests was related to relative average risk for real nests in these territories (based on data collected two years before and two years after the experiment). Nest predation on artificial nests did predict relative predation risk for real nests only when quail egg depredation was used as the criterion for artificial nest predation. Despite plasticine egg depredation being the most common type of predation it was not associated with predation risk for real nests. Small mice and vole species dominated among cases with only plasticine egg depredation, while predatory mammals and snakes destroyed most quail eggs in artificial nests and most eggs in real wheatear nests. The results suggest that artificial nests may only predict the risk for real nests when the nest predator species are similar among the two types of nest. Furthermore, our data suggest that small mice and vole species rarely depredate nests of mid‐sized passerine birds. Our results cast doubt on many previous conclusions based on experiments with artificial nests, since predation risk for such nests is likely to be uncorrelated with risk for real nests due to nest‐type‐specific differences in nest preying species.

Predation risk of age-0 cod ( Gadus) relative to depth and substrate in coastal waters

Among individuals of a species, mean size in fishes increases with depth in the marine environment according to Heincke's Law. Atlantic cod ( Gadus morhua L.), like many young fish, are distributed in shallow (<10 m) coastal water through much of their range as young juveniles (age 0) and deeper water as they grow. We tested the hypothesis that juvenile cod occupy such shallows to minimize risk of encounter with larger piscivorous fish whose mean size also increases with depth according to Heincke's Law. In day and night seining, we found that age-0 cod were most abundant in vegetated sites regardless of time period. In vegetated sites, age-0 cod abundance declined at night; the reverse was true at non-vegetated sites. Piscivorous fish were generally most abundant in vegetated sites; there were no consistent differences in abundance between day and night. Relative risk of predation of individual age-0 cod in different habitats, depths and times was determined by tethering. Age-0 cod prey were tethered 25 cm off the bottom in water 0.7, 1.5, 3, 6, 10 and 20 m deep; six times during the day, three times during dusk and three times during the night in 25-min sets on eight dates in August and September 1998. A total of 576 tether sets were deployed. We deployed tethers on two dates for each of two vegetated—eelgrass, Zostera marina L.—and two unvegetated sites. Predation on tethered prey was lower at night than during day and dusk at all locations and depths. During day and dusk, predation increased with depth at all sites (∼3 times higher in deep compared to shallow). At shallow locations (≤3 m), predation on tethered prey was generally higher in unvegetated compared to vegetated sites during the day and dusk. Predators were captured in 12% of sets. In order of frequency, these were: cunner Tautogolabrus adspersus Walbaum, Atlantic cod, and Greenland cod, G. ogac Richardson. Mean size of all predator species captured increased with depth. We showed that predation risk for juvenile fish increases with depth suggesting a behavioural antipredation mechanism for Heincke's Law.

The Response of a Selfish Herd to an Attack from Outside the Group Perimeter

According to the selfish herd hypothesis, animals can decrease predation risk by moving toward one another if the predator can appear anywhere and will attack the nearest target. Previous studies have shown that aggregations can form using simple movement rules designed to decrease each animal's Domain of Danger. However, if the predator attacks from outside the group's perimeter, these simple movement rules might not lead to aggregation. To test whether simple selfish movement rules would decrease predation risk for those situations when the predator attacks from outside the flock perimeter, we constructed a computer model that allowed flocks of 75 simulated fiddler crabs to react to one another, and to a predator attacking from 7 m away. We attacked simulated crab flocks with predators of different sizes and attack speeds, and computed relative predation risk after 120 time steps. Final trajectories showed flight toward the center of the flock, but curving away from the predator. Path curvature depended on the predator's size and approach speed. The average crab experienced a greater decrease in predation risk when the predator was small or slow moving. Regardless of the predator's size and speed, however, predation risk always decreased as long as crabs took their flock-mates into account. We conclude that, even when flight away from an external predator occurs, the selfish avoidance of danger can lead to aggregation.

Role of surface chemical signals in egg cannibalism and intraguild predation in ladybirds (Coleoptera: Coccinellidae)

The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the surface of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony.

Criteria Determining Behavioural Responses to Multiple Predators by a Stream Mayfly

McIntosh. A. R. and Peckarsky, B. L. 1999. Criteria determining behavioural responses to multiple predators by a stream mayfly - Oikos 85: 554-564. We investigated prey responses to multiple predators by observing drift and positioning of Buetis bicuudctrus (Ephemeroptera: Baetidae) nymphs in the presence of non-feeding brook trout (Salvelinusfontinalis chemical cues) and predatory stoneflies (Megtrrcj,~ signura with glued mouths). In experiments carried out in stream-side channels Baeti.~ antipredator behaviour differed markedly in response to each predator separately: they drifted away from stoneflies. and reduced exposure and drift levels in the presence of trout odour. When both predator cues were presented together the effect of stoneflies, which were observed more frequently at night. depended on the time of day and was modified by presence of fish odour. During the day Buetis responses to both predators were hierarchical as drift and the number on stone tops was reduced whenever fish odour was present regardless of the presence of stoneflies. At night when stoneflies were foraging, Baetis behaviour reflected a compromise between avoiding both predators, with responses to both predators being intermediate between that characteristic of stonefly avoidance (entering the drift) and that characteristic of fish avoidance (drift avoidance). The switch in antipredator behaviour from 'hierarchy' to 'compromise' between multiple predators reflects changes in the relative risk of predation during the day and night. During the day visually feeding trout present a higher predation risk. but at night when stoneflies are foraging and trout visual systems are less effective. the predation risks become more similar. We found no evidence for 'accumulative' avoidance where the magnitude of avoidance increases in response to the number of predators present. because avoiding stoneflies conflicted with avoiding trout. We predict that predator avoidance will take place in the form of a 'hierarchy' when one predator presents substantially higher predation risk than another; 'compromise' behaviour will be observed when the predation risk presented by two predators is more equivalent, but avoiding one predator conflicts with avoiding another; and 'accumulative' antipredatory responses will be observed only when responses to different predators do not conflict. We emphasise that investigation of the responses of prey to multiple predators is important to our understanding of natural communities. and is likely to reveal details about the mechanisms determining the outcome of interactions involving multiple predators.

Relative intensity of predation on the French grunt, Haemulon flavolineatum , during diurnal, dusk, and nocturnal periods on a coral reef

Established hypotheses state that the rate of predation on coral reef fish should be highest during crepuscular periods (dawn and dusk) intermediate diurnally, and lowest nocturnally. We examined the relative risk of predation on juvenile French grunts (Haemulon flavolineatum Desmarest) during diurnal, dusk, and nocturnal periods on the fore- and back-reef at Teague Bay, U.S. Virgin Islands in July and August 1996. Tethering-devices recorded the exact amount of time between attaching a prey fish to its tether and subsequent predation on the prey fish. As tethering of prey usually inflates the actual rate of predation, times from our tethering devices were used to establish only the relative predation risk among treatments. During 3-h diurnal and nocturnal tethering experiments, relative predation was significantly higher during the nocturnal period, and differences between side of reef were not significant. In 30-min tethering experiments, which included all three time periods, the relative predation risk was significantly higher during dusk and nocturnal periods than during the diurnal period. Relative predation was not significantly different between the dusk and nocturnal periods, or between side of reef during any time period. The unexpected finding that the diurnal period had the lowest relative risk of predation indicates that the timing of predation events on reefs, as well as the adaptive reasons for nocturnal larval settlement, may need to be re-examined.

Rapid size-specific changes in the drift of Baetis bicaudatus (Ephemeroptera) caused by alterations in fish odour concentration.

Chemical cues from fish can alter the behaviour of stream invertebrates in experimental tanks but their effect in natural streams has received little attention. By adding brook trout (Salvelinus fontinalis) odour to a trout stream in the Rocky Mountains of Colorado, USA, we tested whether changes in the concentration of chemical cues from visually feeding predatory fish would alter the drift of mayfly nymphs (Ephemeroptera). Stream water was piped from stream-side tanks with (odour) and without (control) three brook trout to two locations in the stream 3.5 m upstream of drift nets at six replicate sites. Five-minute drift samples were collected downstream from odour and control pipes before, during and after the release of water from the tanks into the stream during both the day and night. Almost all drift occurred at night and consisted predominantly of Baetis bicaudatus nymphs. The odour manipulation had no measurable effect on Baetis drift during the day but statistical power was low. During the night, however, the drift of large (>0.65 mm head capsule width, HCW) Baetis nymphs decreased significantly during the odour addition compared to control drift. In contrast, the drift of small nymphs (≤0.65 mm HCW) increased both during and after the odour addition in comparison to control drift. Since the stream contains brook trout (0.04-0.18 m-2), and water from the stream (presumably containing fish odour) altered the behaviour of fishless-stream Baetis nymphs in another experiment, we conclude that the changes in Baetis drift density were a response to an increase in the concentration of fish odour in the stream. Furthermore, we were able to detect the effect within 5 min. of odour addition, indicating that mayfly behavioural response to trout odour was rapid. These results suggest that mayflies can distinguish different concentrations of trout odour in natural streams and that the response is size-specific, according to the relative risk of predation of large and small Baetis.

Spatial and Temporal Variation in Risk to Piscivory of Age-0 Rainbow Trout: Patterns and Population Level Consequences

Abstract We used tethering to measure spatial and temporal patterns of relative risk of predation to age-0 rainbow trout Oncorhynchus mykiss over 2 years in five lakes that varied widely in the abundance of piscivorous rainbow trout. During the day, the most risky habitats were just above the thermocline near the substrate and in open water at the same depth. Risk was intermediate at the surface in the littoral zone and at the surface over the intersection of the thermocline and the lake bottom. The least risky habitat was at the surface in the open water. The intensity and spatial pattern of relative predation risk changed at dusk. The most risky habitat was still at the thermocline–lake bottom intersection, but it was more than twice as risky as during the day. At dusk, relative predation risk increased in the littoral zone and at the surface above the thermocline–lake bottom intersection. The open-water habitats, both at the surface and at the thermocline, had a low relative predation risk. Age-0 and o...

Morphological Adaptations to Predation Risk in Passerines

Avoiding predation is an important factor in avian life-history strategies and there are many examples of adaptations that appear to decrease predation risk. However, we are not aware of any studies of structural morphological adaptations to reduce predation risk in any avian species. Here, we have compared published indices of relative predation risk for passerine species with two size-constrained measures of wingtip shape and relative hind limb morphology. Our analyses indicate that species with rounded wingtips and those with relatively short femora compared with tarsi are at a lower relative predation risk than those with more pointed wingtips and relatively longer femora. These relations are discussed in terms of the functional morphology of wingtip shape and hind limb morphology and suggestions for further experimental investigations are made.

Quantifying Predation Risk for Refuging Animals: A Case Study with Golden Marmots

AbstractAlthough a variety of behaviors expose animals to some risk of predation, there is no accepted way to compare their relative risk. For animals that retreat to refugia when alarmed by predators, the proportion of time devoted to each out‐of‐refuge behavior multiplied by the total time required to return to a refuge can be used to compare a behavior's relative predation risk. Total time to return to a refuge is a function of both response time ‐ the time required to respond to an increased risk of predation — and travel time — the time required to flee to a refuge once alarmed. Quantifying these components can illustrate how animals minimize exposure to predators. Golden marmots (Marmota caudata aurea) were a refuging prey species used to examine the utility of this measure and to understand how marmots minimized their risk of exposure to predation. Golden marmots devoted different amounts of time to looking, foraging, self‐grooming, and playing. To estimate the behavior‐specific time required to return to refugia, the location of different activities was noted and a behavior‐specific travel time was calculated. Alarm calls were played back to marmots engaged in different behaviors to determine, in a standardized manner, if there were behavior‐specific response times. Marmots appeared to minimize their predation risk by performing most behaviors close to refugia. Results suggest that foraging was the riskiest behavior, largely because marmots foraged far from refugia and spent about 30% of their time foraging. While sample sizes were small, results also suggested that play, a rare adult behavior, exposed animals to predation because of a relatively long response time.

The effect of predator presence on body mass in captive greenfinches

Many passerines wintering in temperate regions rely on their energy reserves for survival during periods when foraging is not possible. Excessive fat reserves, however, increase body mass and thus reduce agility and speed in flight, imposing a survival cost when the bird tries to escape from predators. If fat reserves reflect a trade-off between starvation and predation risks, the size of reserves could be expected to vary with the perceived level of predation risk. The hypothesis that increasing the relative risk of predation results in decreased body mass was tested experimentally using captive greenfinches,Carduelis chlorisGreenfinches show winter fattening and take flight when disturbed and are therefore suitable for testing the hypothesis. The perceived predation risk, a stuffed predator moved in the birds’ environment, resulted in lower body mass. Handling the birds had the same effect. These results support theoretical predictions and some field data regarding the adjustment of body mass to variation in the predation risk. They further suggest, in line with other studies, that birds are able to change body mass in response to proximate factors.

Prey selection by sparrowhawks,Accipiter nisus: relative predation risk for breeding passerine birds in relation to their size, ecology and behaviour

Predation is a fundamental ecological process, but there are few studies of predation risk for adult, breeding birds. In this study, we quantified Relative Predation Risk (RPR) for 46 species of passerine birds preyed on by sparrowhawks during the breeding season in south-western Sweden. The sparrowhawk is a major predator of smaller birds in Eurasian forests and woodland. Near nesting hawk pairs, prey abundance was estimated by line transects. From prey remains at hawk nests, we estimated the frequency of prey species in the diet of hawks. For each hawk pair, RPR values for different prey species were calculated. The mean RPR for each prey species, based on hawk pairs as sample units, indicated degree of overrepresentation (positive RPR) or underrepresentation (negative RPR) of the prey in the diet. Prey species with a high positive RPR nested mainly near human habitations (villages or towns), at forest edges and in farmland. However, there were marked seasonal changes in RPR. Forest birds, such as the goldcrest and wren, had the highest RPR in April. Later, the hawks seemed to hunt mainly in the habitats mentioned above, where prey were more abundant or easier to catch, resulting in increasing RPR for the house sparrow, yellowhammer, greenfinch and other species. RPR values were analysed in relation to prey body size (mass) and relative density, as well as prey foraging height and nest height (categorized from the literature). In addition, the mean perch height and mean exposure of prey species were quantified in the field. Most predation was due to the smaller male hawks, providing food for their mates and young, RPR increased with prey body size up to a mass of about 40 g, then declined with increasing body size (larger prey being more difficult to catch), RPR decreased with increasing relative density of prey species. Nest height was not correlated with RPR, but foraging height seems to be an important factor: RPR decreased with increasing foraging height. A similar result was found for mean perch height, when larger prey (over 40 g) and singing individuals were excluded from the field data. RPR increased with mean exposure of prey species when larger prey and singing birds were excluded; a combination of perch height and exposure improved the correlation with RPR. Singing birds were generally perched high in the vegetation and may not suffer high predation risk, contrary to common belief. The results of this study are discussed in relation to temporal and geographical variation in RPR and antipredator adaptations in passerine birds.

Spatial ecology of the crayfishProcambarus alleni in a Florida wetland mosaic

We investigated patterns of differential habitat occupation by the crayfishProcambarus alleni, a numerically abundant and trophically important species in freshwater marsh systems of southern Florida. Crayfish were collected from emergent wet prairies and sloughs in marshes forming the headwaters of the St. Johns River, Florida between August 1992 and December 1993. In addition to differences in plant species composition, wet prairies had greater plant biomass and lower water depths than sloughs. Mean density and biomass of crayfish were significantly higher in the densely vegetated wet prairies (28 per m2; 26.9 g per m2) than in aquatic sloughs (3 per m2; 1.5 g per m2). Crayfish density increased with increasing plant biomass (i.e., habitat complexity) in wet prairies, whereas crayfish density decreased with increasing water levels (i.e., hydroperiod) within slough habitats. Recruitment occurred throughout the study, and the majority of crayfish collected were small in size (<1.0 g). Ovigerous females were rarely collected and were found only in wet prairies. Differences in relative risk of predation, food availability, or a combination of these factors are likely generating differences in habitat occupation by the crayfishP. alleni in this wetland habitat mosaic. Efforts to restore and manage freshwater marshes in southern Florida (e.g., Everglades, Lake Okeechobee, Kissimmee River, St. Johns River) would benefit by considering spatial aspects of the ecology of indicator taxa such as crayfish.

The Selfish Herd Revisited: Do Simple Movement Rules Reduce Relative Predation Risk?

Over two decades ago, W. D. Hamilton argued that animal grouping behavior could evolve if individuals selfishly avoided predation by reducing their domains of danger (Voronoi polygons). We examined this hypothesis through dynamic simulations of individual movement directed by a nearest-neighbor and other simple rules. Results from 500 simulations of 100 individuals moving towards their nearest neighbors for 100 moves (time-steps) showed a 20% increase in relative predation risk and a 1·2% decrease when adjusted for edge effects. This increase was 16% less than that of a random movement rule. When the two rules competed in a two-strategy game simulation, the nearest-neighbor rule always performed better than the random-movement rule with up to 41% differences in relative predation risk. The use of more complicated rules, based on consideration of multiple neighbors, decreased relative predation risk as much as 67%. We conclude that these more complicated, yet still simple movement rules, are adequate to explain the evolution of grouping behavior.

Diel Pattern of Predation Risk in Microtine Rodents

By reviewing information about the activity behaviour of potential predators in northern and central Europe (75 species of mammals, raptors, owls, other birds and snakes) it was examined whether predation risk in microtine rodents varies in the course of the day. Relative predation risk was estimated for four different periods of the 24-h day (dawn, day, dusk and night) by means of an index I pr . This index was calculated on the base of the activity pattern, the degree of prey specialization and the relative abundance of all resident predators in a given area. Day-time appeared as slightly more dangerous than twilight or night when only the activity patterns of potential predators were taken into account. A differentiated analysis including the predators' specialization on microtine prey, however, indicated that higher risk during day-time was mainly due to predators which take microtines only by chance

Female convict cichlids adjust gonadal investment in current reproduction in response to relative risk of brood predation

Parental care theory predicts that investment in current reproduction should be increased when the prospects of success in current reproductive effort are relatively high, and reduced when they are poor relative to expected success from future reproductive effort. A number of studies have shown that levels of postspawning parental investment (brood defence, parents' willingness to risk predation) increase when the brood is augmented. However, few studies have shown a change in pre-spawning (gonadal) investment in response to indirect indicators of reproductive success, such as nest site quality. Convict cichlids (Cichlasoma nigrofasciatum) are small freshwater fish that have biparental care of their young. Pairs of convict cichlids were required to spawn in either "risky" or "secure" spawning caves in the presence of potential egg predators. As predicted by parental care theory, females laid significantly more eggs in secure spawning caves than in risky spawning caves. The ability of this iteroparous fish to adjust gonadal investment in this manner would serve to optimize the use of its resources under varying environmental conditions and ultimately allow it to realize maximize lifetime reproductive success.

Habitat use by bluegill in laboratory pools: where is the refuge when macrophytes are sparse and alternative prey are present?

In northern clear-water systems, bluegill, Lepomis macrochira, select habitats based on relative reward rates and risk of predation. However, because freshwater systems to the south are often turbid, and their resident fish species different, bluegill habitat use patterns may differ from those found in northern clear-water systems. Here I examine the effects of elimination of the inshore macrophyte refuge (an indirect effect of turbidity), and decreased pelagic predation rates on bluegill due to the presence of gizzard shad, Dorosoma cepedianum, in laboratory pools. Bluegill used depths ≤ 20 cm more often with largemouth bass, Micropterus salmoides, than without them; the presence of a preferred alternate prey, gizzard shad, did not affect this behavior. Though bluegill did not alter their habitat use in response to bass activity, they did school more as predator activity increased. Even in the presence of a preferred alternate prey without macrophytes, bluegill continue to use shallow ‘littoral’ areas to avoid predation.