Abundance Of Alternative Prey Research Articles

Optimal Foraging Theory Explains Feeding Preferences in the Western Pacific Crown-of-Thorns Sea Star Acanthaster sp.

AbstractThe selectivity of crown-of-thorns sea stars (Acanthaster sp.) for different coral prey types was quantified in the field and laboratory and compared with a range of nutritional and food quality parameters as well as the growth performance of sea stars fed on different types of coral. Growth rates of small juvenile Acanthaster sp. without previous exposure to coral fed for 6.6 months on 15 individual species of corals showed that the highest rates of growth were achieved on the same types of corals for which adult sea stars show the strongest preference, both in the field and in controlled aquarium conditions. Small Acanthaster sp. (ca. 20 mm, 0.5 g) fed on Acropora formosa, Stylophora pistillata, Seriatopora hystrix, and Pocillopora damicornis increased in size by an average of 9.2-10.7 mm (4.2-5.6 g) per month, compared with 0.1-0.4 mm (0.004-0.028 g) per month on coralline algae fed controls and species such as Porites lutea, Porites lichen, Lobophyllia hemprichii, and Turbinaria mesenterina. Field studies on the same reef where the parents of these juvenile sea stars were collected demonstrated a strong sequential preference for acroporid and then pocilloporid corals, with faviid, merulinid, and poritid corals selected significantly less frequently than other corals when their relative abundance was taken into account. This order of preference by adult field-collected sea stars was confirmed and exhibited even more emphatically in aquarium experiments, where the relative abundance of prey species could be controlled. The growth experiments and measurements of comparative food value between preferred and non-preferred coral prey suggest that feeding preferences in Acanthaster sp. for Acropora and pocilloporids arose consistent with optimal foraging theory and evolved in response to this species being able to feed successfully and efficiently. The high abundance and, therefore, encounter rate of Acropora and pocilloporids is not considered to be an important factor in the evolution of feeding preferences, although relative abundance of alternative prey does affect selectivity. Individual growth and population fitness and reproductive output of Acanthaster sp. will be enhanced by preferential feeding on acroporid and pocilloporid corals, reinforcing the importance of optimal foraging theory in the evolution of feeding preferences.

Co-occurring predators increase biotic resistance against an invasive prey

The presence of multiple predators can lead to variation in predator behavior and ultimately altered risk for shared prey. This concept has seldom been accounted for in studies that consider predator-driven biotic resistance from native marine predators against invasive prey. This study compared the prey selection of whelks and rock lobsters when co-occurring and when foraging in isolation. When in isolation, both predators preferred the native mussel Choromytilus meridionalis, regardless of the abundance of alternative prey. However, when co-occurring, predation risk for all prey species, including the invasive mussel Semimytilus algosus, increased. This was largely driven by greater variation in prey selection by rock lobsters in the presence of whelks. This indicates that predatory efforts from co-occurring predators can result in stronger predation pressure on invasive prey than would be recognized if predators were assessed in isolation.

Effects of environmental conditions on reproductive effort and nest success of Arctic‐breeding shorebirds

The Arctic is experiencing rapidly warming conditions, increasing predator abundance, and diminishing population cycles of keystone species such as lemmings. However, it is still not known how many Arctic animals will respond to a changing climate with altered trophic interactions. We studied clutch size, incubation duration and nest survival of 17 taxa of Arctic‐breeding shorebirds at 16 field sites over 7 years. We predicted that physiological benefits of higher temperatures and earlier snowmelt would increase reproductive effort and nest survival, and we expected increasing predator abundance and decreasing abundance of alternative prey (arvicoline rodents) to have a negative effect on reproduction. Although we observed wide ranges of conditions during our study, we found no effects of covariates on reproductive traits in 12 of 17 taxa. In the remaining taxa, most relationships agreed with our predictions. Earlier snowmelt increased the probability of laying a full clutch from 0.61 to 0.91 for Western Sandpipers, and shortened incubation by 1.42 days forarcticolaDunlin and 0.77 days for Red Phalaropes. Higher temperatures increased the probability of a full clutch from 0.60 to 0.93 for Western Sandpipers and from 0.76 to 0.97 for Red‐necked Phalaropes, and increased daily nest survival rates from 0.9634 to 0.9890 for Semipalmated Sandpipers and 0.9546 to 0.9880 for Western Sandpipers. Higher abundance of predators (foxes) reduced daily nest survival rates only in Western Sandpipers (0.9821–0.9031). In contrast to our predictions, the probability of a full clutch was lowest (0.83) for Semipalmated Sandpipers at moderate abundance of alternative prey, rather than low abundance (0.90). Our findings suggest that in the short‐term, climate warming may have neutral or positive effects on the nesting cycle of most Arctic‐breeding shorebirds.

Increased overwinter mortalities of white-tailed deer (Odocoileus virginianus) fawns during a drought year

Mortality rates of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) fawns have been quantified throughout North America. Few studies, however, have assessed cause-specific mortality of fawns after the first 3 months of life or during a severe weather event. During 2010–2014, we captured and radio-tracked 93 fawns in southern and central Illinois and recorded 18 mortality events. In order of importance, survival rates were affected by days since capture, year of drought, age at capture, week after capture (1 or 0 indicator), and region. Estimated overwinter (fall through spring) survival rate (±SE) of fawns in both regions during 2010–2014 was 0.83 ± 0.04. However, estimated overwinter survival rates were depressed during 2012–2013, following the severe drought of 2012 (0.63 ± 0.11 or 0.66 ± 0.11 depending on the model). Main causes of mortality were capture-related and predation, though some dead deer also showed signs of hemorrhagic disease. We suspect that the extreme drought of 2012 created favorable conditions for fall–spring mortality of fawns, due to elevated disease transmission and lower forage quality and quantity for deer. In addition, drought may have contributed to predation by reducing abundance of alternative prey. Our results suggest that severe weather conditions during summer can substantially impact overwinter fawn survival.

Effect of habitat complexity on the predation ofBuenoa fuscipennis(Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well-known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2(nd) instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.

Chinook Salmon Foraging Patterns in a Changing Lake Michigan

AbstractSince Pacific salmon stocking began in Lake Michigan, managers have attempted to maintain salmon abundance at high levels within what can be sustained by available prey fishes, primarily Alewife Alosa pseudoharengus. Chinook Salmon Oncorhynchus tshawytscha are the primary apex predators in pelagic Lake Michigan and patterns in their prey selection (by species and size) may strongly influence pelagic prey fish communities in any given year. In 1994–1996, there were larger Alewives, relatively more abundant alternative prey species, fewer Chinook Salmon, and fewer invasive species in Lake Michigan than in 2009–2010. The years 2009–2010 were instead characterized by smaller, leaner Alewives, fewer alternative prey species, higher abundance of Chinook Salmon, a firmly established nonnative benthic community, and reduced abundance of Diporeia, an important food of Lake Michigan prey fish. We characterized Chinook Salmon diets, prey species selectivity, and prey size selectivity between 1994–1996 and 2009–2010 time periods. In 1994–1996, Alewife as prey represented a smaller percentage of Chinook Salmon diets than in 2009–2010, when alewife comprised over 90% of Chinook Salmon diets, possibly due to declines in alternative prey fish populations. The size of Alewives eaten by Chinook Salmon also decreased between these two time periods. For the largest Chinook Salmon in 2009–2010, the average size of Alewife prey was nearly 50 mm total length shorter than in 1994–1996. We suggest that changes in the Lake Michigan food web, such as the decline in Diporeia, may have contributed to the relatively low abundance of large Alewives during the late 2000s by heightening the effect of predation from top predators like Chinook Salmon, which have retained a preference for Alewife and now forage with greater frequency on smaller Alewives.

The seasonal diet of British pine marten determined from genetically identified scats

AbstractKnowledge of a carnivore's foraging behaviour is central to understanding its ecology. Scat‐content analysis provides a non‐invasive way to collect such information but its validity depends on attributing scats to the correct species, which can prove problematic where similarly sized species occur sympatrically. Here we provide the first description of the diet of European pine marten Martes martes in Scotland based on genetically identified scats (n = 2449). Concurrent small mammal live trapping also allowed us to determine preferential selection of small mammal species. We found the marten diet was almost entirely formed by three principal foods: Microtus agrestis (39%), berries (Sorbus aucuparia and Vaccinium myrtillus: 30%) and small birds (24%). The seasonal dominance of these foods in the diet suggested a facultative foraging strategy, with a short period in which the diet was more generalized. A discrepancy in the occurrence of Microtus in the diet (77% of small mammals consumed) and marten home ranges (12% of small mammals trapped) indicated a frequency‐independent preference for this prey, one which differentiated British marten from marten in continental Europe. Microtus were the marten's staple prey and taken with relative consistency throughout the year, even at times when rodent populations were at their least abundant. Martens supplemented their diet with small birds and fruits as these foods became abundant in summer. The diet became generalized at this time, reflected by a threefold increase in diet niche breadth. Microtus consumption was significantly reduced in autumn, however, when their populations peak in abundance. The autumn diet was instead dominated by fruit; an abrupt dietary switch suggesting a frequency‐dependent preference for fruit irrespective of the abundance of alternative prey.

Effects of Intercropping With Flowering Plants on Predation ofOstrinia nubilalis(Lepidoptera: Crambidae) Eggs by Generalist Predators in Bell Peppers

Bell pepper plots intercropped with flowering plants were measured for improving biological control provided by natural enemies of the European corn borer [Ostrinia nubilalis (Hübner)]. The intercropped plants Dill, Anethum graveolens L.; coriander, Coriandrum sativum L.; and buckwheat, Fagopyrum escuelentum Moench; were established on the edge of two pepper plots and compared with nonintercropped control plots. Predation by the three species Orius insidiosus Say; Coleomegilla maculata DeGeer; and Chrysoperla, sp. Stephens, was monitored by installing O. nubilalis egg masses on sentinel plants in 2008, 2009, and 2010. To assess negative impacts of alternative prey on O. nubilalis egg predation, green peach aphid, Myzus persicae (Sulzer) populations were monitored via whole-plant counts in 2009 and 2010. Myzus persicae densities on pepper plants peaked in June or July and then declined rapidly. Predation on O. nubilalis eggs increased rapidly after aphid populations declined. Aphid populations were reduced in two out of three field-seasons in intercropped plots. Seasonal predation by O. insidiosus was significantly higher in the intercropped system four out of five field-seasons and one field season by C. maculata. Results indicate that biocontrol of O. nubilalis can be improved by intercropping with flowering plants, although this capacity may depend on the abundance of alternative prey.

Scale and the guild functional response: Density-dependent predation varies with plot size

The predator functional response is an important mechanism determining the persistence of prey species; however, little is known about the effects of spatial scale on the functional response. We used a manipulative field experiment to quantify the effects of plot size on the guild functional response on the clam Mercenaria mercenaria, replicating the experiment in the summer in Chesapeake Bay, Virginia, and in the spring and fall in Indian River Lagoon, Florida, to examine the effects of predator and alternative prey abundance. In Virginia, the predation rate increased with both patch size and predator density, and was described by a modified sigmoid Type III functional response model that incorporated the effects of patch size. In Florida in the spring, the predator functional response was a Type III and did not vary with plot size, but in the fall it was a linear Type I at small plot sizes, and a Type III at a larger plot size. We hypothesize that the difference is primarily driven by changes in predator abundance and species between sites. In showing that the functional response can vary with plot size and season, our results indicate that small-scale experiments do not always scale up spatially or temporally. We suggest that the predictive power of such experiments may be limited by the complexity of the food web.

Factors influencing diet variation in a generalist predator across its range distribution

Factors linked with intraspecific variation in trophic diversity are still poorly understood in generalist species like the Montagu’s harrier (Circus pygargus) but may have important implications for conservation management at a wide scale. We described geographic patterns of Montagu’s harrier diet across Eurasia, gathering diet data from 30 studies in 41 areas from 11 countries. We grouped prey as invertebrates, reptiles, small mammals, large mammals, eggs, small birds and large birds, and calculated the contribution of each prey type to the diet (as % biomass) and Shannon’s Diversity Index for each study site. We analysed qualitative estimates of prey abundance in relation to latitude and longitude, then diet composition in relation to habitat of the study area and prey abundance estimates. Diet diversity of Montagu’s harriers increased from north to south, while abundance of all prey groups other than small mammals showed the opposite trends. Agricultural areas in northern latitudes seemed to hold high densities of small mammals, but low densities of alternative prey. Overall, birds were the main prey in most of Montagu’s harrier’s distribution range, although the relative importance of each prey type in the diet was significantly explained by its local abundance and habitat, confirming the opportunistic foraging strategy of this raptor species. Consumption of mammals was an exception to this trend, being negatively associated with the abundance of alternative prey, suggesting that this prey is not preferred. Trophic diversity in this species could be influenced by land-use changes through variations in the abundance and availability of prey, which could impact its population dynamics. This may be particularly important for northern populations of Montagu’s harriers breeding in agricultural habitats, where trophic diversity is already low.

Citrus-orchard ground harbours a diverse, well-established and abundant ground-dwelling spider fauna

Ground-dwelling spider assemblages comprise one of the most representative predatory groups to be found in manycrops. There is some evidence of the role that ground-dwelling spiders play in controlling certain citrus pests; however, thereare almost no studies about the abundance and composition of this predatory group in citrus orchards. A three-year surveyconducted using pitfall traps in three citrus orchards in Eastern Spain yielded more than five-thousand ground-dwellingspiders belonging to more than 50 species and 20 families. Wandering families such as Lycosidae, Gnaphosidae andZodariidaewere the most numerous in terms of captures. The generalist predator Pardosa cribata Simon (Araneae: Lycosidae) was the most common species, representing a quarter of all captures, followed by Zodarion cesari Pekar. (Araneae: Zodariidae) and Trachyzelotes fuscipes (Koch) (Araneae: Gnaphosidae). Spiders were active throughout the year with a peak population in summer. The species abundance data for the three spider assemblages sampled fitted a log normal statistical model which is consistent with a well-established community. The presence of a cover crop provided higher abundance of alternative prey and consequently higher abundance and diversity of ground-dwelling spiders. This work demonstrates that the citrus-orchard ground harbours a diverse and abundant ground-dwelling spider fauna, which is also active throughout the year. A challenge for future studies will be to establish conservation management strategies for these predators, that will improve biological control of those citrus pests that inhabit or spend part of their life cycle on the orchard floor.

Chick starvation in yellow‐eyed penguins: Evidence for poor diet quality and selective provisioning of chicks from conventional diet analysis and stable isotopes

AbstractThe link between poor reproductive success and diet was investigated in yellow‐eyed penguins Megadyptes antipodes, by assessing diet at two localities separated by about 30 km: the north coast of Stewart Island where breeding success is low (0.38–0.67 chicks per pair in recent years), and Codfish Island where breeding success is higher (0.96–1.51 chicks per pair), and relating this to published data from South Island localities, where average breeding success was 1.1 chicks per pair. Diet composition, meal sizes and energetic content of meals and prey were determined from stomach contents, and stable isotope analyses of chick down, fledgling feathers and adult blood provided information on diet throughout the fledging period. The high proportion of stomachs that were empty or lacked diagnostic remains reduced sample size considerably, and variability between samples reduced the power to detect significant differences in meal size, proportions of empty stomachs and prey diversity of meals. Energetic content of Stewart Island meals was less than Codfish Island meals, and there was a non‐significant trend for smaller meal sizes and reduced prey diversity among Stewart Island samples. Both localities had lower prey diversity and smaller meals than South Island penguins. Blue cod Parapercis colias accounted for 99% of prey biomass in Stewart Island and 70% in Codfish Island stomach samples, where 27% of prey biomass was opalfish Hemerocoetes monopterygius. Isotopic mixing models carried out on larger sample sizes indicated that opalfish comprised a large proportion of the diet at both locations, with adults selectively provisioning chicks with opalfish while feeding mainly on blue cod themselves. We suggest the large blue cod consumed by Codfish Island and Stewart Island penguins, larger than those consumed by South Island penguins, is difficult to transfer to chicks by regurgitation. Oyster dredging around Stewart Island may have reduced the availability and abundance of alternative prey to Stewart Island penguins.

Web Orientation and Prey Resources for Web-Building Spiders in Eastern Hemlock

We examined the arthropod community on eastern hemlock, Tsuga canadensis (L.) Carr, in the context of its role in providing potential prey items for hemlock-associated web-weaving spiders. Using sticky traps simulating spider webs, we evaluated what prey items are available to web-weaving spiders in eastern hemlock based on web orientation (horizontal versus vertical) and cardinal direction. We found that the overwhelming majority (>70%) of prey items available to spiders in hemlock canopies were Diptera. Psocoptera, Hymenoptera, and Hemiptera comprised most of the remaining potential prey. A significant direction × orientation interaction, and greater trap capture in some direction-orientation combinations, suggests that spiders might locate their webs in eastern hemlock canopies for thermoregulatory purposes, ultimately optimizing prey capture. We also evaluated these findings in the context of hemlock infestation by the invasive hemlock woolly adelgid, Adelges tsugae Annand. The adelgid is a sedentary insect with a mobile crawler stage that provides a readily available, easily obtained food source for predators in hemlock canopies. However, an abundance of alternative prey will affect within canopy spider distribution and the potential intensity with which spiders consume these prey. Understanding the response of spiders to potential prey availability is essential to understanding the trophic interactions involving these predators and their potential for influencing herbivore populations.

Frass Analysis of Diets of Aphidophagous Lady Beetles (Coleoptera: Coccinellidae) in Utah Alfalfa Fields

Aphidophagous lady beetles enhance their foraging success in natural settings by consuming other types of food in addition to aphids. Frass analysis was used to examine natural diets of female lady beetles in fields of alfalfa (Medicago sativa L.) in northern Utah. The first (spring) alfalfa crop was censused in 2004 and 2005 to determine the diet of female adults of the introduced Coccinella septempunctata L., and two native species, C. transversoguttata richardsoni Brown, and Hippodamia convergens Guerin. The proportion of females of the three lady beetle species that fed on pea aphids [Acyrthosiphon pisum (Harris)] and alfalfa weevil larvae [Hypera postica (Gyllenhal), an abundant alternative prey] increased from early to late season during the first crop. A corresponding seasonal decrease occurred in the proportion of females consuming other types of arthropods (e.g., thrips and collembolans) and nonarthropod food (pollen and fungal spores). Overall, frass analysis indicated that the diets of C. septempunctata and the two native species in alfalfa were similar in their inclusion of a broad variety of foods. The study shows that frass analysis can provide a good overview of the diets of lady beetles in natural settings.

Influence of habitat patch characteristics on the success of upland duck nests

When there is a rich guild of nest predators that use different modalities and techniques to locate hidden nests, we hypothesized that no habitat patch characteristic will consistently predict nest success, because if such a characteristic existed then predators would develop a search image based on it and use that characteristic to increase their hunting effi ciency for nests. We tested this prediction in the Prairie Pothole region of North Dakota by characterizing the features of 16 habitat patches that contained >1,800 dabbling duck nests. Nest success was monitored during both the early and late nesting season over 2 years. Nest success was generally low and highly variable among habitat patches and across seasons and years. We found that nest success was rarely correlated with patch size, nest density, predator abundance and richness, abundance of alternative prey for predators, and visual and physical obstruction provided by the vegetation. Those few habitat patch characteristics that were correlated with nest success during a particular single year or season were not correlated during other seasons or years. Hence, our results supported the hypothesis that no habitat

Effect of mosquitofish (Gambusia affinis) and sestonic food abundance on the invertebrate community within a constructed treatment wetland

Summary1. The effect of mosquitofish (Gambusia affinis) predation on the invertebrate community in a hypereutrophic constructed treatment wetland in southern California was investigated at two nutrient levels that influenced sestonic food abundance.2. Gambusia affinis and insect predators in the wetland had a significant impact on larval mosquito density in the wetland irrespective of nutrient level. At the end of the 5‐month study, cladoceran abundance in predator exclusion enclosures was 2–3 orders of magnitude greater than in the treatments that allowed access by planktivores. Chironomids were the most abundant insect group collected in emergence traps, and midge production from the high nutrient location of the wetland was greater than from the low nutrient location, but was not affected significantly by G. affinis. The presence of abundant alternative prey in this highly enriched wetland may have weakened the predation impact of G. affinis on mosquitoes.3. The abundances of six invertebrate groups in dipper samples and of four insect groups in emergence trap collections were analysed using a multivariate distance‐based linear model. Fish treatment and location interactions with sampling date explained significant amounts of the variation in the abundance of invertebrate groups.4. Multivariate multiple regression analysis showed that chlorophyll‐a concentration explained a large portion of the variability in non‐predatory insect and zooplankton abundance at the high nutrient location, whereas bacterial density explained a large portion of the variability in the abundances of these taxa at the low nutrient location. Predatory insects were not directly coupled to the bottom‐up influence of bacterial abundance and chlorophyll‐a.

Aggregation of polyphagous predators in response to multiple prey: ladybirds (Coleoptera: Coccinellidae) foraging in alfalfa

AbstractThe spatial distribution of polyphagous predators may often reflect the integration of aggregative responses to local densities of multiple species of prey, and as such may have consequences for the indirect linkages among the prey sharing these predators. In a factorial field experiment in which we manipulated local prey densities within a field of alfalfa in Utah (USA), we tested whether aphidophagous ladybirds would aggregate not only in response to their primary aphid prey, but also in response to an abundant alternative prey, the alfalfa weevil (Hypera postica [Gyllenhal]). Native North American ladybirds (primarily Hippodamia convergens Guerin and H. quinquesignata quinquesignata [Kirby]) responded only to spatial variation in aphid density. In contrast, the introduced ladybird, Coccinella septempunctata L., aggregated also at local concentrations of the weevil late in the experiment when weevil density was high and aphid density was relatively low throughout all experimental plots. The results support the hypothesis that C. septempunctata is more responsive than are native ladybirds to the availability of alternative prey in alfalfa, which may account in part for the displacement of native ladybirds from alfalfa by the introduced species as aphid numbers have declined. The differing responses of the native and introduced ladybirds to spatial patterns of the alternative prey underscore the importance of extending the study of predator aggregation to understand better how polyphagous predators distribute themselves in response to spatial patterns of multiple species of potential prey.

GIZZARD SHAD PUT A FREEZE ON WINTER MORTALITY OF AGE-0 YELLOW PERCH BUT NOT WHITE PERCH

Four decades of observations on the limnology and fishes of Oneida Lake, New York, USA, provided an opportunity to investigate causes of mortality during winter, a period of resource scarcity for most juvenile fishes, in age-0 yellow perch (Perca flavescens) and age-0 white perch (Morone americana). This time series contains several environmental (e.g., winter severity) and biological (e.g., predator abundance) signals that can be used to disentangle multiple effects on overwinter mortality of these fishes. A multiple regression analysis indicated that age-0 yellow perch winter mortality was inversely related to fish length in autumn and to the abundance of alternative prey (gizzard shad [Dorosoma cepedianum] and white perch). However, no length-selective predation of yellow perch by one of the main predators, adult walleye (Sander vitreus), was detected. In contrast, white perch mortality was directly associated with total predator biomass and abundance of white perch in autumn, and inversely related to yellow perch abundance as a potential buffer species, but not to the abundance of gizzard shad. Winter severity was not a significant predictor of mortality for either perch species. Predicted winter starvation mortality, from a model described in the literature, was much lower than observed mortality for yellow perch. Similar models for white perch were correlated with observed mortality. These results collectively suggest that predation is the main mechanism shaping winter mortality of yellow perch, while both predation and starvation may be important for white perch. This analysis also revealed that gizzard shad buffer winter mortality of yellow perch. Although winter duration determines the northern limit of fish distributions, in mid-latitude Oneida Lake and for these species, predator-prey interactions seem to exert a greater influence on winter mortality than starvation.

Do Top-Down Or Bottom-Up Forces Determine Stephanitis Pyrioides Abundance In Urban Landscapes?

This study examined the influence of habitat structural complexity on the collective effects of top-down and bottom-up forces on herbivore abundance in urban landscapes. The persistence and varying complexity of urban landscapes set them apart from ephemeral agroecosystems and natural habitats where the majority of studies have been conducted. Using surveys and manipulative experiments. We explicitly tested the effect of natural enemies (enemies hypothesis), host plant quality, and herbivore movement on the abundance of the specialist insect herbivore, Stephanitis pyrioides, in landscapes of varying structural complexity. This herbivore was extremely abundant in simple landscapes and rare in complex ones. Natural enemies were the major force influencing abundance of S. pyrioides across habitat types. Generalist predators, particularly the spider Anyphaena celer, were more abundant in complex landscapes. Predator abundance was related to greater abundance of alternative prey in those landscapes. Stephanitis pyrioides survival was lower in complex habitats when exposed to endemic natural enemy populations. Laboratory feeding trials confirmed the more abundant predators consumed S. pyrioides. Host plant quality was not a strong force influencing patterns of S. pyrioides abundance. When predators were excluded, adult S. pyrioides survival was greater on azaleas grown in complex habitats, in opposition to the observed pattern of abundance. Similarly, complexity did not affect S. pyrioides immigration and emigration rates. The complexity of urban landscapes affects the strength of top-down forces on herbivorous insect populations by influencing alternative prey and generalist predator abundance. It is possible that habitats can be manipulated to promote the suppressive effects of generalist predators.

Effect of Conservation Strips on the Abundance and Distribution of Natural Enemies and Predation of <I>Agrotis ipsilon</I> (Lepidoptera: Noctuidae) on Golf Course Fairways

Habitat manipulation in the form of beetle banks and flowering insectary strips has been a successful method to increase natural enemy and alternative prey abundance. In this study, beetle banks and flowering insectary strips were combined to create conservation strips as refuge for a variety of natural enemies in golf course ecosystems. Conservation strips were installed in the roughs next to golf course fairways. Pitfall traps were used to monitor the abundance of predatory, parasitoid, alternative prey, and pest insects in the roughs and fairways near conservation strips and in roughs and fairways without conservation strips (controls). In addition, Agrotis ipsilon (Hufnagel) larvae were placed in the roughs and fairways to evaluate the effect of conservation strips on the predation of pests. Conservation strips were successful at increasing predator, parasitoid, and alternative prey abundance in golf course fairways and roughs overall. Increases were most evident within 4 m of conservation strips. Moreover, predation of A. ipsilon larvae was greater in fairways adjacent to conservation strips than fairways adjacent to roughs only. Differences in predation did not correspond to differences in predator abundance in the fairways, suggesting “predator abundance” may not be the most reliable estimate of the effect of habitat manipulations. These results suggest conservation strips could be an important new tool in conservation biological control on golf courses and may be applicable in other agro-ecosystems. Other methods of estimating and enhancing the effects of conservation strips are discussed.