Prey Supply Research Articles

Longitudinal variation in energy flow networks along a large subtropical river, China

To understand the longitudinal variation in the structure and functioning of large river ecosystems, six Ecopath models were constructed to exhibit the energy flows of aquatic food webs along the subtropical East River in China. Input parameters were primarily obtained from field data collected in 2012–2016; model outputs were estimated by network analysis. Longitudinally, ecosystem characteristics of the East River had high spatial heterogeneity. The biomass, production, and consumption, of which >75.8% of each was distributed at trophic level (TL) II, were determined by aquatic insects upstream, molluscs midstream, and zooplankton downstream. Carnivorous fish occupied the maximal TL of 2.95–3.50. Due to the different trophic interactions of regional food webs, the keystone groups shifted from odonate larvae in headwaters to piscivorous fish upstream/midstream, to zooplankton downstream, and to phytoplankton near the estuary. Aquatic insects, insectivorous fish, epiphytes, and hydrophytes, all of which had ecotrophic efficiencies >0.99, were critical groups that influenced mass balance through short prey supply. The mean transfer efficiencies (TEs) through TLs IIIV had the lowest values of 1.8–4.1% upstream and increased to the highest levels of 8.0–8.4% midstream before they decreased to 6.4–7.0% downstream. The low TEs along the river were limited mainly by the lack of carnivorous fish upstream and the low predation on mollus and plankton midstream/downstream. A series of theory and information indices showed that the pristine upstream system was mature but underdeveloped in organisation; in contrast, the downstream systems in the urban and industrial reaches were immature and stressed in terms of excessive phytoplankton production and short cycling.

Muddy waters: Efficacious predation of container-breeding mosquitoes by a newly-described calanoid copepod across differential water clarities

Mosquito-borne diseases induce unrivalled morbidity and mortality in human populations. In recent times, greater urbanisation has facilitated vector population expansion, particularly of those which proliferate in container-style habitats. To combat increased associated disease risk, we urgently require innovative and efficacious control mechanisms to be identified and implemented. Predatory biological control of vectorially-important mosquitoes can be effective. Despite their high prevalence in freshwater ecosystems, predatory calanoid copepods have yet to be examined comprehensively for mosquito control. Moreover, environmental context-dependencies can cause substantial variations in natural enemy impacts on target populations. Accordingly, improved understanding of the effects of context-dependencies upon predatory biocontrol is needed. Here, we use functional responses (FRs) to examine the predatory impact of a newly-described species of calanoid copepod, Lovenula raynerae, upon larval Culex pipiens prey across variations in prey supply and water clarity. Using outdoor field trials, we assess the viability of L. raynerae in reducing mosquito survival in container-style habitats. Lovenula raynerae displayed destabilising Type II FRs towards larval mosquito prey across all water clarities tested, with overall predation rates remaining largely unaffected across all clarity treatments. In the outdoor experiment, L. raynerae applications resulted in substantial reductions in larval C. pipiens populations, with close to total eradication achieved following the experimental period under higher predator densities. These results demonstrate that environmental context such as water clarity may have little effect on vector control by calanoid copepods, which suggests a predatory reliance on hydromechanical signalling. Further, for the first time, we demonstrate the applicability of calanoid copepods to artificial container-style habitats where mosquitoes proliferate. Therefore, our results indicate that further examination into the applicability of this species group to aid vector biocontrol strategies is warranted.

Otolith chemistry as a fisheries management tool after flooding: The case of Missouri River gizzard shad

AbstractReduced river–floodplain connectivity can decrease fisheries production and cause ecological and socioeconomic consequences. In 2011, the largest flood on record in the Missouri River since 1898 nearly eliminated connectivity between an embayment (Hipple Lake) and Lake Sharpe, impeding movement of walleye (Sander vitreus) and a forage fish, gizzard shad (Dorosoma cepedianum). Thus, we used otolith chemistry to quantify Hipple Lake's natal contribution to Lake Sharpe's gizzard shad population and forecast effects of connectivity loss on the reservoir's socioeconomically important walleye fishery. Fish were classified to natal habitats with 79–89% accuracy, with most gizzard shad (64%) hatching in floodplain habitats (i.e., embayments, tributaries, canals, and stilling basins). Hipple Lake contributed 12% of gizzard shad to Lake Sharpe, more than a tributary (4%) and embayment (0%) but less than a canal (27%) and stilling basin (21%). Hipple Lake (178 acres) covers 0.31% of Lake Sharpe (56,884 acres), so its natal contribution is 38 times what would be expected if contribution was linearly related to area. Sediment and water management to maintain connectivity between Lake Sharpe and Hipple Lake and other floodplain habitats is important for continued gizzard shad production and prey supply for the walleye fishery. Otolith chemistry facilitates assessment of gizzard shad natal contributions in different habitats, serving as a fisheries management tool to inform floodplain habitat protection and rehabilitation after floods.

Notes on life history and field efficiency of Cybocephαlus fodori predator of Quαdrαspidiotus perniciosus in Northern Greece

Sampling results during 1978-1979 and 1981-1982 in two heavily-infested almond orchards in Northern Greece showed a high mortality of the San Jose scale. A considerable part of this mortality was attributable to indigenous entomophagous insects, especially predators. Among them, Cybocephalus fodori Endrody-Younga (Coleoptera: Nitidulidae) appeared to be the key species. Field observations showed that C. fodori hibernates as an adult, forming aggregations. C. fodori reared in outdoor cages showed full adult activity by end March. Given an abundant supply of prey, the insect develops two complete and a third partial generations per year. Under constant conditions (25±2° C, 65±5% R.H. and 16 hrs light per day), the development of its three larval instars was completed in about 19 days and the pupal stage lasted about 10 days. On average, 68 Quadraspidiotus perniciosus Comstock (Homoptera: Diaspididae) adult females were partly consumed per larva of C. fodori. Individually deposited eggs and young larvae were found under the covers of the San Jose scales.

Trends in Rainbow Trout Recruitment, Abundance, Survival, and Growth during a Boom‐and‐Bust Cycle in a Tailwater Fishery

AbstractData from a large‐scale mark–recapture study were used in an open‐population model to determine the cause for long‐term trends in growth and abundance of a Rainbow TroutOncorhynchus mykisspopulation in the tailwater of Glen Canyon Dam, Arizona. Reduced growth affected multiple life stages and processes, causing negative feedbacks that regulated the abundance of the population, including higher mortality of larger fish; lower rates of recruitment (young of the year) during years when growth was reduced; and lower rates of sexual maturation in the following year. High and steady flows during spring and summer 2011 resulted in a very large recruitment event. The population had declined tenfold by 2016 due to a combination of lower recruitment and reduced survival of larger trout. Survival rates for 225‐mm and larger Rainbow Trout in 2014, 2015, and 2016 were 11, 21, and 22% lower, respectively, than average survival rates between 2012 and 2013. Abundance at the end of the study would have been threefold to fivefold higher if survival rates for larger individuals had remained at the elevated levels estimated for 2012 and 2013. Growth declined between 2012 and 2014 owing to reduced prey availability, which led to very poor fish condition (~0.90–0.95) by fall 2014. Poor condition in turn resulted in low survival rates of larger fish during fall 2014 and winter 2015, which contributed to the population collapse. In Glen Canyon, large recruitment events driven by high flows can lead to population increases that cannot be sustained due to limitations in prey supply. When the ability to regulate prey supply is lacking, flows that reduce the probability of large recruitment events can be used to avoid boom‐and‐bust population cycles. Our study demonstrates that mark–recapture is a very informative approach for understanding the dynamics of tailwater trout populations.Received December 6, 2016; accepted March 31, 2017 Published online August 2, 2017

Earning their Stripes: The Potential of Tiger Trout and Other Salmonids as Biological Controls of Forage Fishes in a Western Reservoir

AbstractMaintaining a balance between predator and prey populations can be an ongoing challenge for fisheries managers, especially in managing artificial ecosystems such as reservoirs. In a high‐elevation Utah reservoir, the unintentional introduction of the Utah Chub Gila atraria and its subsequent population expansion prompted managers to experimentally shift from exclusively stocking Rainbow Trout Oncorhynchus mykiss to also stocking tiger trout (female Brown Trout Salmo trutta × male Brook Trout Salvelinus fontinalis) and Bonneville Cutthroat Trout O. clarkii utah (hereafter, Cutthroat Trout) as potential biological control agents. We measured a combination of diet, growth, temperature, and abundance and used bioenergetic simulations to quantify predator demand versus prey supply. Utah Chub were the predominant prey type for tiger trout, contributing up to 80% of the diet depending on the season. Utah Chub represented up to 70% of the total diet consumed by Cutthroat Trout. Although Utah Chub dominated the fish biomass in the reservoir, we still estimated abundances of 238,000 tiger trout, 214,000 Cutthroat Trout, and 55,000 Rainbow Trout. Consequently, when expanded to the population level of each predator, tiger trout and Cutthroat Trout consumed large quantities of Utah Chub on an annual basis: tiger trout consumed 508,000 kg (2,660 g/predator) of the standing prey population, and Cutthroat Trout consumed an estimated 322,000 kg (1,820 g/predator). The estimated combined consumption by Cutthroat Trout and tiger trout exceeded the estimate of Utah Chub annual production. As such, our results suggest that the high rates of piscivory exhibited by Cutthroat Trout and tiger trout in artificial lentic ecosystems are likely sufficient to effectively reduce the overall abundance of forage fishes and to prevent forage fishes from dominating fish assemblages. Collectively, this research provides the first documented findings on tiger trout ecology and performance, which will aid managers in designing and implementing the best stocking strategy to optimize sport fish performance, control undesirable forage fish, and enhance and maintain angler satisfaction.Received April 1, 2016; accepted November 8, 2016 Published online March 8, 2017

Aggregative and feeding thresholds of sympatric rorqual whales within a fjord system

AbstractRorqual whales (f. Balaenopteridae) supposedly respond to increases in prey supply according to both aggregative and feeding thresholds. With the former, they gather in areas above a minimum prey density set by their basal metabolic needs. With the latter, feeding occurs only above a prey density set by the energetic cost of lunge feeding. To compare prey preferences and the two threshold types in sympatric rorquals, I conducted systematic transect surveys and behavioral observations of humpback whales (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) in a British Columbia fjord system. While multiple prey features were found to influence whale aggregation and feeding, both threshold types were observed in each species' response to krill volume. Humpback response to prey features was less predictable and influenced by more factors than that of fin whales, which appeared to be exclusively euphausivorous and interested in the deepest high‐volume krill patches within the deepest channels. Compared with fin whales, humpbacks found higher‐volume krill patches and had higher aggregative thresholds, but had lower feeding thresholds. Findings aligned overall with the expectations that aggregative behavior is responsive to local prey supply, while feeding thresholds are governed by less mutable energetic constraints imposed by body size and feeding mode. Both aggregative and feeding threshold responses appeared to be a function of local conditions: As total krill‐like backscatter increased, feeding thresholds stabilized (became more nonlinear and more nonrandom), while aggregative thresholds destabilized. All results emphasized the importance of incorporating observations of feeding effort in studies of prey preference and habitat use.

Responses of wolf feeding habits after adverse climatic events in central-western Belarus

Many studies have investigated the ecology of wolf populations of Eurasia, showing that although wolves are mostly opportunistic in seeking meso-large enough mammalian prey, they can also be selective, depending on local availability of prey and their population biomass. Yet prey preferences of the wolf have been poorly evaluated in situations of complex predator/prey systems because such ecological situations are extremely rare in Europe. In particular, the role of beaver is poorly known due to the extreme decline in its range and population over the last few centuries.We conducted a 15-year study (1999–2014) of wolf Canis lupus diet in the Naliboki forest of central-western Belarus to determine the dietary responses of the wolf population in a context of a rich prey supply (beaver 650inds/100km2, elk 47inds/100km2, red deer 98inds/100km, roe deer 398inds/100km2, wild boar 234inds/100km2). The bison, although present, is not preyed on. We compared the seasonal and annual diet variations of both wolf adults and pups, by scat analysis and hair identification. In winter 2012–2013, the winter was quite harsh with a long period of snow, which severely affected the roe deer and wild boar populations. Five severe summer droughts also occurred (1999, 2001, 2002, 2004 and 2013), greatly decreasing the water level in rivers and canals. We took advantage of these stressful events to evaluate the diet responses of the wolves.In “normal” years, we identified 11 food categories, essentially beaver and medium-sized ungulates (66%), and large ungulates to a lesser extent (9% in summer, 20% in winter). The adults were found to selectively supply pups with beaver, probably because of its easy transportability. Beaver consumption also increased during summer droughts when water levels were very low. After the harsh winter of 2012–2013, which was followed by a sharp decline in medium-sized prey, we observed a shift in the winter diet breadth of the wolves towards greater consumption of both large wild ungulates and small carnivores. We concluded that:1. Beaver is a functional element in wolf ecology, as a primary food for adults and pups;2. A large range of available prey species is important to maintaining a viable wolf population in cases of extreme climatic events.

Trophic Feasibility of Reintroducing Anadromous Salmonids in Three Reservoirs on the North Fork Lewis River, Washington: Prey Supply and Consumption Demand of Resident Fishes

AbstractThe reintroduction of anadromous salmonids in reservoirs is being proposed with increasing frequency, requiring baseline studies to evaluate feasibility and estimate the capacity of reservoir food webs to support reintroduced populations. Using three reservoirs on the north fork Lewis River as a case study, we demonstrate a method to determine juvenile salmonid smolt rearing capacities for lakes and reservoirs. To determine if the Lewis River reservoirs can support reintroduced populations of juvenile stream‐type Chinook Salmon Oncorhynchus tshawytscha, we evaluated the monthly production of daphnia Daphnia spp. (the primary zooplankton consumed by resident salmonids in the system) and used bioenergetics to model the consumption demand of resident fishes in each reservoir. To estimate the surplus of Daphnia prey available for reintroduced salmonids, we assumed a maximum sustainable exploitation rate and accounted for the consumption demand of resident fishes. The number of smolts that could have been supported was estimated by dividing any surplus Daphnia production by the simulated consumption demand of an individual Chinook Salmon fry rearing in the reservoir to successful smolt size. In all three reservoirs, densities of Daphnia were highest in the epilimnion, but warm epilimnetic temperatures and the vertical distribution of planktivores suggested that access to abundant epilimnetic prey was limited. By comparing accessible prey supply and demand on a monthly basis, we were able to identify potential prey supply bottlenecks that could limit smolt production and growth. These results demonstrate that a bioenergetics approach can be a valuable method of examining constraints on lake and reservoir rearing capacity, such as thermal structure and temporal food supply. This method enables numerical estimation of rearing capacity, which is a useful metric for managers evaluating the feasibility of reintroducing Pacific salmon Oncorhynchus spp. in lentic systems.Received April 24, 2016; accepted July 28, 2016 Published online October 11, 2016

Harmful effects of Dinophysis to the ciliate Mesodinium rubrum: Implications for prey capture

Toxigenic Dinophysis spp. are obligate mixotrophic dinoflagellates that require a constant supply of prey—Mesodinium rubrum—to achieve long-term growth by means of kleptoplasty. Mesodinium rubrum is, however, a fast moving, jumping ciliate exhibiting an effective escape response from suspensivorous predators. In the present study, a series of laboratory experiments evaluating the motility and survival of M. rubrum in the presence of Dinophysis cells and/or substances contained in their culture medium was designed, in order to assess the mechanisms involved in prey capture by Dinophysis spp. Cell abundance of M. rubrum decreased in the presence of Dinophysis cf. ovum cells producing okadaic acid (OA; up to 7.94±2.67pgcell−1) and smaller amounts of dinophysistoxin-1 (DTX-1) and pectenotoxin-2 (PTX-2). Prey capture was often observed after the ciliate had been attached to adhesive “mucus traps”, which only appeared in the presence of Dinophysis cells. Before being attached to the mucus traps, M. rubrum cells reduced significantly their swimming frequency (from ∼41 to 19±3 jumps min−1) after only 4h of initial contact with D. cf. ovum cells. M. rubrum survival was not affected in contact with purified OA, DTX-1 and PTX-2 solutions, but decreased significantly when the ciliate was exposed to cell-free or filtered culture medium from both D. cf. ovum and D. caudata, the latter containing moderate concentrations of free eicosapentaenoic acid and docosahexaenoic acid. The results thus indicate that Dinophysis combines the release of toxic compounds other than shellfish toxins, possibly free PUFAs, and a “mucus trap” to enhance its prey capture success by immobilizing and subsequently arresting M. rubrum cells.

Slow and fast development in two aphidophagous ladybirds on scarce and abundant prey supply.

Developmental rates are highly variable, both within and between genotypes and populations. But the rationale for two differential (slow and fast) developmental rates within same cohort under varying prey supply has yet not been explored. For this purpose, we investigated the effect of scarce and abundant prey supply on slow and fast development at 27°C in two aphidophagous ladybirds, Menochilus sexmaculatus (Fabricius) and Propylea dissecta (Mulsant) and its effect on their body mass and reproductive attributes. The ladybirds were provided with scarce and abundant supply of Aphis craccivora Koch under standardized abiotic conditions in the laboratory. A clear bimodal (two peaks, where the first peak represented the fast developing individuals and the second peak slow developing individuals) pattern of distribution for both prey supplies was obtained, which got skewed with change in prey supply. On abundant prey supply, more fast developing individuals (139 M. sexmaculatus and 123 P. dissecta) were found and less (46 M. sexmaculatus and 36 P. dissecta) on scarce prey supply. Slow developing individuals had female biased sex ratio, higher longevity and lower body mass. Fast developing females laid higher number of eggs with higher egg viability. Results of the study are indicative of occurrence and constancy of the slow and fast developing individuals in the egg batch.

Acoustic Communication in Fishes and Potential Effects of Noise.

Many soniferous fishes such as cods and groupers are commercially important. Sounds are produced during courtship and spawning, and there is the potential for aquatic noise to interfere with critical behaviors and affect populations. There are few data on the response of wild populations of sound-producing fishes to acoustic noise. New motion and sound exposure fish tags could be used to assess the behavioral responses of large numbers of fish to noise exposure. Many factors, such as fishing mortality and environmental variability in prey supply, could also affect populations and potentially interact with the behavioral responses to noise.

Spider assemblage (Arachnida: Araneae) associated with canopies of Vochysia divergens (Vochysiaceae) in the northern region of the Brazilian Pantanal

This study describes the composition and temporal variation of the spider assemblage (Arachnida: Araneae) associated with canopies of Vochysia divergens Pohl. (Vochysiaceae) in the northern region of the Brazilian Pantanal. Three V. divergens plants were sampled in 2004, at each seasonal period of the northern Pantanal (high water, receding water, dry season and rising water), using thermonebulization of the canopies with insecticide, totaling 396 m2 of sampled canopies. Analysis of abundance and richness of spider families were based on Non-Metric Multidimensional Scaling (NMDS) and Variance Analysis (ANOVA and MANOVA). A total of 7,193 spiders were collected (6,330 immatures; 88.0%; 863 adults, 12.0%) distributed in 30 families. Araneidae (1,676 individuals), Anyphaenidae (1,631 individuals), Salticidae (1,542 individuals) and Pisauridae (906 individuals), were predominant, representing 80.0% of the sample. Ten different guilds were registered: aerial hunters, orb-weavers, nocturnal aerial runners and diurnal space web weavers dominated, sharing most ecological niches. The spider assemblage is affected by changes in the habitat structure, especially by the seasonal hydrological regime and variations in the phenology of V. divergens . The assemblage is composed of different groups of spiders. The dominant taxa and behavioral guilds differ in the different seasonal periods. Spiders were more abundant during the dry and rising water seasons, most likely reflecting a greater supply of potential prey, associated with new foliage and flowering at the canopy. The displacement of soil dwelling spiders to the trunks and canopies before and during the seasonal floods can change the structure and composition of the canopy assemblages. Oonopidae, Gnaphosidae and Caponiidae, were more frequent during the rising and high water seasons, which indicates that these taxa use the canopies of V. divergens as a refuge during the seasonal flooding in the Pantanal.

Dissolved ions mediate body mass gain and predatory response of an invasive fish

Ecological impacts of invasive species are mediated by the environmental characteristics of the invaded habitats. The invasive round goby Neogobius melanostomus is a brackish-water adapted invader with high predatory and competitive impacts on native communities. We test the hypothesis that both body mass gain and predation rates of the round goby are reduced in low-dissolved ion waters in which they can establish, using calcium (Ca2+) as a focal ion of great importance to the physiology of aquatic animals. Round gobies were first acclimated for 36 days on a diet of shrimp pellets in either high (35 mg L−1) or low (12 mg L−1) Ca2+ concentration [Ca]. We then assessed the functional response (FR)—the relationship between predation rate and prey supply—of the round goby from high and low [Ca] on amphipod prey in either condition. Round gobies in high [Ca] consumed more pellets during the acclimation period and gained more mass compared to fish in low-[Ca] conditions. Functional response experiments revealed that round gobies at high-[Ca] levels for both acclimation and FR experiments had the highest predatory impact, whereas fish in low-[Ca] FR treatments had similarly low predation rates regardless of acclimation [Ca]. In a second experiment, non-acclimated round gobies had a higher FR on mayfly nymph prey at high [Ca] than fish at low-[Ca] levels. Our results indicate that the round goby has stronger ecological impacts in conditions that are more physiologically optimal for the species. Identifying key physico-chemical factors that mediate impacts of invaders would help prioritize habitats for management attention.

Ecological impacts of invasive alien species along temperature gradients: testing the role of environmental matching.

Invasive alien species (IAS) can cause substantive ecological impacts, and the role of temperature in mediating these impacts may become increasingly significant in a changing climate. Habitat conditions and physiological optima offer predictive information for IAS impacts in novel environments. Here, using meta-analysis and laboratory experiments, we tested the hypothesis that the impacts of IAS in the field are inversely correlated with the difference in their ambient and optimal temperatures. A meta-analysis of 29 studies of consumptive impacts of IAS in inland waters revealed that the impacts of fishes and crustaceans are higher at temperatures that more closely match their thermal growth optima. In particular, the maximum impact potential was constrained by increased differences between ambient and optimal temperatures, as indicated by the steeper slope of a quantile regression on the upper 25th percentile of impact data compared to that of a weighted linear regression on all data with measured variances. We complemented this study with an experimental analysis of the functional response (the relationship between predation rate and prey supply) of two invasive predators (freshwater mysid shrimp, Hemimysis anomala and Mysis diluviana) across. relevant temperature gradients; both of these species have previously been found to exert strong community-level impacts that are corroborated by their functional responses to different prey items. The functional response experiments showed that maximum feeding rates of H. anomala and M. diluviana have distinct peaks near their respective thermal optima. Although variation in impacts may be caused by numerous abiotic or biotic habitat characteristics, both our analyses point to temperature as a key mediator of IAS impact levels in inland waters and suggest that IAS management should prioritize habitats in the invaded range that more closely match the thermal optima of targeted invaders.

Using non-systematic surveys to investigate effects of regional climate variability on Australasian gannets in the Hauraki Gulf, New Zealand

Few studies have investigated regional and natural climate variability on seabird populations using ocean reanalysis datasets (e.g. Simple Ocean Data Assimilation (SODA)) that integrate atmospheric information to supplement ocean observations and provide improved estimates of ocean conditions. Herein we use a non-systematic dataset on Australasian gannets (Morus serrator) from 2001 to 2009 to identify potential connections between Gannet Sightings Per Unit Effort (GSPUE) and climate and oceanographic variability in a region of known importance for breeding seabirds, the Hauraki Gulf (HG), New Zealand. While no statistically significant relationships between GSPUE and global climate indices were determined, there was a significant correlation between GSPUE and regional SST anomaly for HG. Also, there appears to be a strong link between global climate indices and regional climate in the HG. Further, based on cross-correlation function coefficients and lagged multiple regression models, we identified potential leading and lagging climate variables, and climate variables but with limited predictive capacity in forecasting future GSPUE. Despite significant inter-annual variability and marginally cooler SSTs since 2001, gannet sightings appear to be increasing. We hypothesize that at present underlying physical changes in the marine ecosystem may be insufficient to affect supply of preferred gannet main prey (pilchard Sardinops spp.), which tolerate a wide thermal range. Our study showcases the potential scientific value of lengthy non-systematic data streams and when designed properly (i.e., contain abundance, flock size, and spatial data), can yield useful information in climate impact studies on seabirds and other marine fauna. Such information can be invaluable for enhancing conservation measures for protected species in fiscally constrained research environments.

A spatio‐temporal contrast of the predatory impact of an invasive freshwater crustacean

AbstractAimImpacts of invasive species may vary across invasion gradients, owing to trait‐based sorting of individuals through dispersal: those aggregating at invasion fronts may be more aggressive and voracious. We examine, in the field and laboratory, variation in the predatory impacts of an invasive Ponto‐Caspian crustacean Hemimysis anomala G.O. Sars, 1907 at two sites along a spatio‐temporal gradient of invasion.LocationRepublic of Ireland.MethodsWe used reciprocal transplant field‐deployed mesocosms to compare predation rates of invasion front and well‐established H. anomala on natural zooplankton assemblages. In the laboratory, we measured the functional response (relationship between predation rate and prey supply) of H. anomala from both sites, for a per capita mechanistic comparison of predation efficiency. We also assessed prey selectivity of H. anomala in the mesocosm experiments to further compare feeding behaviour. Finally, we used a correlative approach to assess the community impact of H. anomala across sites, including a nearby uninvaded site, by comparing zooplankton diversities and densities.ResultsInvasion front H. anomala had higher predation rates than well‐established H. anomala at high in situ zooplankton densities. Invasion front H. anomala also had higher functional responses – in particular showing higher ‘attack rates’ – indicating a heightened ability to locate and capture prey. Prey selectivity was consistent across the spatio‐temporal contrast, with positive selection for cladocerans. Zooplankton diversity and density declined with time since H. anomala invasion, both being maximal at the uninvaded site.Main conclusionsOur study, for the first time, (1) reveals differences in predatory per capita effects and associated behavioural traits between two sites along a spatio‐temporal invasion gradient and (2) shows a negative community‐level impact of the invasive H. anomala in natural water bodies. Further spatio‐temporal comparisons of predatory per capita effects of invaders are needed to assess the generality of these results.

Complementary Diet of Cathartes burrovianus (Cathartidae) With Fruit Elaeis guineensis (Arecaceae)

The mangrove swamps of the Guapi-Mirim Environmental Protection Area are rich in animal diversity. Due to its considerable size there is a generous supply of prey for any predator as well as significant food resources for animal scavengers. The vultures, which are carrion or predatory birds are included in the order Cathartiformes (Cathartidae) and the most common species in Brazil are: Cathartes aura (Linnaeus, 1758), Cathartes burrovianus Cassin, 1845; Cathartes melambrotus Wetmore, 1964; Coragyps atratus (Bechstein, 1793) and Sarcoramphus papa (Linnaeus, 1758). In the mangrove swamps of this protected area three species of vultures are commonly seen: C. aura, C. burrovianus e C. atratus. These three species basically have a diet of animal carcasses. All the Cathartes burrovianus observations carried out in this study were made in a small part of the mangrove swamps in the Guapi-Mirim APA, located in the district of Itambi, Itaboraí, Rio de Janeiro, Brazil. The observations were made every two weeks for a year and photography was used to record the birds. A total of 78 photographic observations were made of these birds (C. burrovianus) feeding on the fruit of the oil palm Elaeis guineensis Jacq. 1897. As the mangrove swamp has abundant food resources throughout the year, it was concluded that C. burrovianus feeds on the fruits of the palm E. guineensis not only as an alternative food in the absence of carcasses, but also a complement to their dietary needs. It is the first record of this feeding behavior. This fact may be related to the higher digestibility of carcasses consumed by these animals.

Density-dependent intraspecific aggression regulates survival in northern Yellowstone wolves (Canis lupus).

Understanding the population dynamics of top-predators is essential to assess their impact on ecosystems and to guide their management. Key to this understanding is identifying the mechanisms regulating vital rates. Determining the influence of density on survival is necessary to understand the extent to which human-caused mortality is compensatory or additive. In wolves (Canis lupus), empirical evidence for density-dependent survival is lacking. Dispersal is considered the principal way in which wolves adjust their numbers to prey supply or compensate for human exploitation. However, studies to date have primarily focused on exploited wolf populations, in which density-dependent mechanisms are likely weak due to artificially low wolf densities. Using 13 years of data on 280 collared wolves in Yellowstone National Park, we assessed the effect of wolf density, prey abundance and population structure, as well as winter severity, on age-specific survival in two areas (prey-rich vs. prey-poor) of the national park. We further analysed cause-specific mortality and explored the factors driving intraspecific aggression in the prey-rich northern area of the park. Overall, survival rates decreased during the study. In northern Yellowstone, density dependence regulated adult survival through an increase in intraspecific aggression, independent of prey availability. In the interior of the park, adult survival was less variable and density-independent, despite reduced prey availability. There was no effect of prey population structure in northern Yellowstone, or of winter severity in either area. Survival was similar among yearlings and adults, but lower for adults older than 6 years. Our results indicate that density-dependent intraspecific aggression is a major driver of adult wolf survival in northern Yellowstone, suggesting intrinsic density-dependent mechanisms have the potential to regulate wolf populations at high ungulate densities. When low prey availability or high removal rates maintain wolves at lower densities, limited inter-pack interactions may prevent density-dependent survival, consistent with our findings in the interior of the park.

Functional response and predatory interactions in conspecific and heterospecific combinations of two congeneric species (Coleoptera: Coccinellidae)

In the present study, the predatory interactions between two locally abundant large lady beetles, Coccinella septempunctata L. (C7) and Coccinella transversalis F. (Ct) provided with either an extremely scarce, scarce, sub-optimal, optimal or abundant supply of the pea aphid, Acyrthosiphon pisum (Harris) were investigated. For this, three 2-predator combinations (conspecific C7 + C7 and Ct + Ct, and heterospecific C7 + Ct) of 10-day-old unmated adult females were used. The relationships between the proportion of prey consumed by the predators in the conspecific and heterospecific combinations when provided with five different abundances of prey were similar in consisting of a decelerating (type II) functional response when provided with an extremely scarce to optimal supply of prey, followed by an accelerating (type III) functional response when provided with an optimal to abundant supply of prey. It is likely that the modified type II functional response recorded in the present study was a consequence of using a small experimental arena (Petri dish). The multiplicative risk model analysis revealed that the predators interacted antagonistically except in the C7 + C7 combination provided with an extremely scarce supply of prey where the predators had an additive effect. The predators in the heterospecific C7 + Ct combination consumed fewer aphids when provided with an extremely scarce, scarce, sub-optimal or optimal supply of prey prey than the predators in conspecific C7 + C7 combination but a similarly high number when provided with an abundant supply of prey. In addition, the efficiency of converting prey biomass into their own biomass was higher in the heterospecific C7 + Ct than in the conspecific C7 + C7 or Ct + Ct combinations at all prey densities. Although the conversion efficiency of the predators in the conspecific and heterospecific combinations provided with an extremely scarce supply of prey was the highest recorded, their growth rate was the lowest. In contrast, both the conversion efficiency and growth rate of the predators in the three combinations were highest when provided with an abundant supply of prey. It may, therefore, be concluded that when the predators in the combinations occupy similar ecological niches, they will probably consume less prey than they require when prey is both scarce and abundant because the predators interact antagonistically.