Availability Of Invertebrate Prey Research Articles

Coping with unpredictable environments: fine-tune foraging microhabitat use in relation to prey availability in an alpine species.

Microhabitat utilisation holds a pivotal role in shaping a species' ecological dynamics and stands as a crucial concern for effective conservation strategies. Despite its critical importance, microhabitat use has frequently been addressed as static, centering on microhabitat preference. Yet, a dynamic microhabitat use that allows individuals to adjust to fine-scale spatio-temporal prey fluctuations, becomes imperative for species thriving in challenging environments. High-elevation ecosystems, marked by brief growing seasons and distinct abiotic processes like snowmelt, winds, and solar radiation, feature an ephemeral distribution of key resources. To better understand species' strategies in coping with these rapidly changing environments, we delved into the foraging behaviour of the white-winged snowfinch Montifringilla nivalis, an emblematic high-elevation passerine. Through studying microhabitat preferences during breeding while assessing invertebrate prey availability, we unveiled a highly flexible microhabitat use process. Notably, snowfinches exhibited specific microhabitat preferences, favoring grass and melting snow margins, while also responding to local invertebrate availability. This behaviour was particularly evident in snow-associated microhabitats and less pronounced amid tall grass. Moreover, our investigation underscored snowfinches' fidelity to foraging sites, with over half located within 10m of previous spots. This consistent useprevailed in snow-associated microhabitats and high-prey-density zones. These findingsprovide the first evidence of dynamic microhabitat use in high-elevation ecosystems and offer further insights into the crucial role of microhabitats for climate-sensitive species. They call for multi-faceted conservation strategies that go beyond identifying and protecting optimal thermal buffering areas in the face of global warming to also encompass locations hosting high invertebrate densities.

Spatiotemporal dynamics in the roosting ecology of the green toad: implications for urban planning and nature conservation

Continuously growing urbanisation and the ongoing rebuilding of urban habitats affect amphibians, the most threatened vertebrate groups. Even though the effects of urbanisation are mostly negative, some artificial components of the urban landscape may also display positive relationships with amphibian populations and therefore work in favour of their persistence in cities. Roosts provide protection from predation, desiccation and offer invertebrate prey availability; therefore, roost availability is an essential necessity of amphibian maintenance in urban areas. On the example of the European green toad Bufotes viridis, a typical urban dweller, we investigated roost-type occupancy and their distribution relative to a breeding pond during the active season (from June to October). The analysis was done with regard to the different life stages of individuals from three urban populations. Green toads used fissures situated in various man-made constructions (e.g., buildings, roads, pathways) for roosting cavities, however without any predominant pattern among toad life stages. The local architecture of the study sites mainly determined the type of occupied roosts. In adults and juveniles we recorded a gradually increased roost distance from breeding pond, while subadults were found roosting further from the water during the active season. Management measures aimed at maintaining a favourable state of green toad populations in urban environments should incorporate a complex of actions that consider general as well as the local ecological patterns of particular populations.

Organic matter sources and flows in tundra wetland food webs.

Arctic lowland tundra is often dominated by wetlands. As numbers and types of these wetlands change with climate warming, their invertebrate biomass and assemblages may also be affected. Increased influx of nutrients and dissolved organic matter (DOM) from thawing peat may alter the relative availability of organic matter (OM) sources, differentially affecting taxa with disparate dependence on those sources. In five shallow wetland types (<40 to 110 cm deep) and in littoral zones of deeper lakes (>150 cm), we used stable isotopes (δ13C, δ15N) to compare contributions of four OM sources (periphytic microalgae, cyanobacteria, macrophytes, peat) to the diets of nine macroinvertebrate taxa. Living macrophytes were not distinguishable isotopically from peat that likely contributed most DOM. Within invertebrate taxa, relative OM contributions were similar among all wetland types except deeper lakes. Physidae snails consumed substantial amounts of OM from cyanobacteria. However, for all other taxa examined, microalgae were the dominant or a major OM source (39-82%, mean 59%) in all wetland types except deeper lakes (20‒62%, mean 31%). Macrophytes and macrophyte-derived peat, likely consumed mostly indirectly as DOM-supported bacteria, ranged from 18‒61% (mean 41%) of ultimate OM sources in all wetland types except deeper lakes (38-80%, mean 69%). Invertebrate consumption of microalgal C may often have involved bacterial intermediates, or a mix of algae with bacteria consuming peat-derived OM. High production of periphyton with very low δ13C values were favored by continuous daylight illuminating shallow depths, high N and P levels, and high CO2 concentrations from bacterial respiration of peat-derived DOM. Although relative OM sources were similar across wetland types except deeper lakes, total invertebrate biomass was much higher in shallow wetlands with emergent vegetation. Impacts of warming on the availability of invertebrate prey to waterbirds will likely depend not on shifts in OM sources, but more on changes in overall number or area of shallow emergent wetlands.

The fear diet: Risk, refuge, and biological control by omnivorous weed seed predators

Weed seed biocontrol by omnivorous mice and insects can limit weed seedbanks, but this ecosystem service can be difficult to predict given the broad diet breadth of seed predators and their potential for intraguild predation. Seed foraging behavior is further modified by fluctuating cues of predation risk from higher trophic levels and the availability of refuge habitat. Uncertainty about whether co-occurring insects and mice additively contribute to weed biocontrol or interfere with each other via intraguild predation limits our ability to recommend habitat management strategies that reliably promote seed destruction. Using seed removal assays, fluorescent powder tracking, and stable isotope analyses, we assessed effects of a predation risk cue (moonlight) on mouse foraging patterns in a patchwork of vegetated and exposed plots in a cultivated field. Mouse foraging activity decreased on exposed ground during the full moon, compared to dark nights, yet foraging movements were unaffected by moon cycle within refuge patches. Weed seed consumption was more than three times higher in cover than exposed soil, and 78% of that difference was attributable to invertebrate granivores. Mice and invertebrate granivores both exhibited higher foraging activity in cover, indicating co-occurrence of intraguild predators and prey. However, stable isotope analyses of fecal samples revealed that mice captured in refuge habitats fed at slightly lower trophic levels than those in exposed habitats (suggesting minimal intraguild predation in refuge habitat), and mouse diet was unaffected by moonlight. Despite increased availability of invertebrate prey in cover patches, mice do not appear to preferentially exploit prey when avoiding their own predators or interfere with weed seed predation. Therefore, functional redundancy of mice and invertebrate seed predators in cover crops and other refuge habitats may strengthen and stabilize weed seed biocontrol.

Coping with drought? Effects of extended drought conditions on soil invertebrate prey and diet selection by a fossorial amphisbaenian reptile.

Arid climates are characterized by a summer drought period to which animals seem adapted. However, in some years, the drought can extend for unusually longer periods. Examining the effects of these current extreme weather events on biodiversity can help to understand the effects of climate change, as models predict an increase in drought severity. Here, we examined the effects of "unusual" extended drought on soil invertebrate prey availability and on diet composition (based on fecal contents) and diet selection of a fossorial amphisbaenian, the checkerboard worm lizard Trogonophis wiegmanni. Weather data show interannual variations in summer drought duration. The abundance and diversity of soil invertebrates in spring were high, and similar to those found in a "normal" early autumn, after some rain had ended with the summer drought. In contrast, in years with "unusual" extended drought, abundance, and diversity of soil invertebrates in early autumn were very low. Also, there were seasonal changes in amphisbaenians' diet; in autumn with drought, prey diversity, and niche breadth decreased with respect to spring and autumns after some rain had fallen. Amphisbaenians did not eat prey at random in any season, but made some changes in prey selection that may result from drought-related restrictions in prey availability. Finally, in spite that amphisbaenians showed some feeding flexibility, their body condition was lower in autumn than in spring, and much lower in autumn with drought. If extended drought became the norm in the future, amphisbaenians might suffer important negative effects for their health state.

Malleefowl Leipoa ocellata incubation mounds as habitat for other vertebrates

Ecosystem engineers change the availability of resources for other species by forming new habitat or modifying existing habitat but, despite the diversity of avian ecosystem engineers, 80% of current literature focuses on mammals and invertebrates. Malleefowl Leipoa ocellata build large incubation mounds of soil and leaf-litter that are likely to provide habitat for invertebrates and vertebrates but use of their mounds by other vertebrates has never been quantified. Here, we examine vertebrate fauna visitation rates at Malleefowl mounds and non-mounds using camera-trap data collected by two citizen science projects. From 2012 to 2018, 20 active Malleefowl mounds and 16 non-mound sites were monitored over 31,913 hours and 225,144 hours, respectively. In total, we identified visits by 1724 birds, reptiles and mammals from 36 species. The mean number of vertebrate visits per 1000 hours of surveillance was around one and a half times and species richness five times that at mounds compared with non-mounds. Malleefowl mounds may enhance the availability of invertebrate prey for insectivorous birds and mammals, provide a favourable microclimate for reptiles to thermoregulate, and be signalling/social communication locations. Our results show that further research is warranted and suggest that conservation of Malleefowl may be important not only for the Malleefowl itself, but also for a suite of mallee birds and reptiles.

Occupancy of avian foraging guilds in soybean fields and borders in Entre R\xedos, Argentina: responses to vegetation structure and prey resources

BackgroundReconciling agriculture and biodiversity conservation is a challenge given the growing demand for agricultural products. In recent decades, Argentina has witnessed agricultural expansion and intensification affecting biodiversity and associated ecosystem services. Within agroecosystems, the level of habitat quality is critical for birds, and may depend on vegetation structure, availability of invertebrate prey, and the use of pesticides. Although the relationship between vegetation structure and avian occurrence has been widely studied, to our knowledge, there are no studies that also incorporate prey availability throughout the cycle of soybean crops in Argentina. We estimated and predicted the effects of land cover and temporal variation on the occurrence of avian foraging guilds in Entre Ríos, Argentina, in order to guide management related to potential ecosystem services provided by birds. We also estimated temporal effects of vegetation structure and insecticides on the main arthropod orders consumed by birds to evaluate prey availability.MethodsWe conducted bird and arthropod surveys for 2 years along transects located in 20 randomly selected soybean fields (N = 60) and their adjacent borders (N = 78) throughout the crop growing season, in four seasons. We estimated avian occupancy, accounting for imperfect detection, and arthropod counts fitting generalized linear mixed models.ResultsThe number of native trees in field borders positively influenced the occurrence of most bird species, mainly insectivores. Granivore foliage gleaners, also were positively affected by grass height. Salliers and aerial foragers were weakly affected by distance to forest and native trees. In general, the availability of invertebrates to birds was highest during the third season. Arthropod counts in borders were greater during the last three crop stages than during the pre-sowing period.ConclusionsWe found that with 10 to 15 native tree species in borders, coupled with a complex vegetation structure with shrubs and grasses, we could conserve a wide spectrum of insectivorous birds, and may contribute to the invertebrate pest control service. Vegetated field borders function as a refuge for arthropods, especially agriculturally beneficial taxa such as Hymenopterans. Finally, several groups of birds use the interior of the fields and could help control pests.

Shifting food web structure during dam removal-Disturbance and recovery during a major restoration action.

We measured food availability and diet composition of juvenile salmonids over multiple years and seasons before and during the world's largest dam removal on the Elwha River, Washington State. We conducted these measurements over three sediment-impacted sections (the estuary and two sections of the river downstream of each dam) and compared these to data collected from mainstem tributaries not directly affected by the massive amount of sediment released from the reservoirs. We found that sediment impacts from dam removal significantly reduced invertebrate prey availability, but juvenile salmon adjusted their foraging so that the amount of energy in diets was similar before and during dam removal. This general pattern was seen in both river and estuary habitats, although the mechanisms driving the change and the response differed between habitats. In the estuary, the dietary shifts were related to changes in invertebrate assemblages following a hydrological transition from brackish to freshwater caused by sediment deposition at the river's mouth. The loss of brackish invertebrate species caused fish to increase piscivory and rely on new prey sources such as plankton. In the river, energy provided to fish by Ephemeroptera, Plecoptera, and Trichoptera taxa before dam removal was replaced first by terrestrial invertebrates, and then by sediment-tolerant taxa such as Chironomidae. The results of our study are consistent with many others that have shown sharp declines in invertebrate density during dam removal. Our study further shows how those changes can move through the food web and affect fish diet composition, selectivity, and energy availability. As we move further along the dam removal response trajectory, we hypothesize that food web complexity will continue to increase as annual sediment load now approaches natural background levels, anadromous fish have recolonized the majority of the watershed between and above the former dams, and revegetation and microhabitats continue to develop in the estuary.

Arthropod Abundance and Biomass in Response to Pinus taeda L. Trunk Height

The trunks of southeastern pines provide vital habitat for many invertebrates that are, in turn, available as prey for bark-foraging birds. Knowing how these arthropods are distributed vertically on tree trunks is important and may allow for a rapid assessment of prey response to forest management practices. In this study, we used a fast-acting insecticide to sample the arthropods on the lower (0–3 m) and upper (3–9 m) bole sections of nine loblolly pine, Pinus taeda L., trees. We collected over 1,600 arthropods representing 15 orders and 66 families. Ants (Hymenoptera: Formicidae) were the most abundant group collected, and wood cockroaches (Blattodea: Blattellidae) accounted for the greatest overall biomass. Abundance and biomass of arthropods per m2 were greater on the lower trunk, but these values were strongly correlated with those from the upper trunk. Nonmetric multidimensional scaling and permutational multivariate analysis of variance showed that arthropod community composition differed significantly between the two trunk positions. Additionally, indicator species analysis found four flightless taxa to be significantly associated with the lower trunk (Araneae, Zygentoma, Hymenoptera, and Pseudoscorpiones) but none with the higher trunk position. These findings show that bark-dwelling arthropods are generally more abundant near the bases of trees and that there is a strong relationship between abundance and biomass between lower and upper trunk sections. Knockdown insecticides offer an effective tool for rapidly assessing the availability of invertebrate prey for bark-foraging birds.

Supplemental food alters nest defence and incubation behaviour of an open‐nesting wetland songbird

Climate‐driven increases in spring temperatures are expected to result in higher prey availability earlier in the breeding season for insectivorous birds breeding in wetland habitats. Predation during the incubation phase is a major cause of nesting failure in open‐nesting altricial birds such as the Eurasian reed warbler. The nest predation rate in this species has recently been shown to be substantially reduced under conditions of experimentally elevated invertebrate prey availability. Food availability near the nest may be an important determinant of adult incubation and nest defence behaviours during the incubation period. We used two experimental studies to compare incubation behaviour and nest defence in food‐supplemented and unsupplemented adult Eurasian reed warblers during the incubation phase. In the first study we measured nest defence behavioural responses to a taxidermic mount of a native predator (stoat Mustela erminea). In the second study we used temperature loggers installed in nests to measure breaks in incubation as a measure of nest vulnerability. Food‐supplemented birds responded aggressively to the presence of a predator more quickly than those in the unsupplemented group, suggesting they are closer to their nest and can more quickly detect a predator in the vicinity. Food‐supplemented birds also had shorter breaks in incubation (both in terms of maximum and mean off‐bout durations), presumably because they were foraging for shorter periods or over shorter distances from the nest. This study therefore identifies the behavioural mechanisms by which changes in food availability may lead to changes in nest survival and thus breeding productivity, in open‐nesting insectivorous birds.

Stream macrophytes increase invertebrate production and fish habitat utilization in a California stream

AbstractStable flow and thermal regimes, coupled with geologically derived nutrients, are drivers of enhanced productivity in volcanic spring‐fed rivers. However, little information exists on biotic mechanisms or species interactions contributing to elevated productivity at higher trophic levels. In a California stream, juvenile steelhead trout were observed to preferentially select macrophyte habitat at a rate three times greater, on average, than five other habitat types. To understand the potential rearing benefits associated with macrophytes, we conducted a manipulative experiment to determine how macrophytes affect invertebrate prey availability and stream water velocity. Macrophytes supported up to nine times greater abundance of invertebrates than adjacent open gravel habitats. They also doubled invertebrate drift rates and reduced water velocity by up to 42‐fold. The results show that aquatic macrophytes are an important stream habitat feature that may be bioenergetically more favourable for rearing salmonids than more traditional lotic habitats. We suggest that macrophytes have the potential to enhance growth rates of juvenile salmonids when compared with other habitat types. Habitats that confer growth and size advantages may ultimately improve fitness and contribute to conservation of imperilled salmonids.

Modification of benthic food web structure by recovering seagrass meadows, as revealed by trophic markers and mixing models

Seagrass meadows are among the most diverse and productive coastal ecosystems in the world. Currently, the accelerating loss of these habitats is recognized worldwide. In the southern Baltic Sea, a natural recovery of Zostera marina meadows has occurred after a dramatic reduction within the last century. The aim of this study is to understand if and how the recovering eelgrass meadows affect the functioning of benthic ecosystems. The trophic links within the benthic food webs in the seagrass meadows and bare sandy bottoms were depicted and compared. The trophic connections were examined by combining stable isotope (SI) composition (δ13C, δ15N) and fatty acid (FA) profiles of meio- and macrofauna consumers and of potential food sources (particulate organic matter, surface sediment organic matter, epiphytes, microphytobenthos/bacteria and macrophytes) in a Bayesian mixing model framework (MixSIAR). Significantly higher amounts of the FA bacterial marker (C18:1ɷ7) were observed in meiofauna (approximately 40%) than in the macrofauna (1% on average), suggesting that bacteria are an important part of the meiofauna diet. The mixing model results indicated that the benthic consumers in the vegetated habitat utilized more food sources (e.g., epiphytes in the diets of meiofauna and macrofaunal grazers) and thus had a more diverse diet. Macrofaunal omnivores relied to a larger degree on animal-derived organic matter in vegetated habitat, which could be linked to higher invertebrate prey availability. The results highlight the importance of recovering seagrass meadows in driving the mechanisms responsible for food web organization. Any type of change to the state of seagrass meadows is crucial to the functioning and stability of marine ecosystems.

Enhanced invertebrate prey production following estuarine restoration supports foraging for multiple species of juvenile salmonids (Oncorhynchus spp.)

Estuaries provide crucial foraging resources and nursery habitat for threatened populations of anadromous salmon. As such, there has been a global undertaking to restore habitat and tidal processes in modified estuaries. The foraging capacity of these ecosystems to support various species of out‐migrating juvenile salmon can be quantified by monitoring benthic, terrestrial, and pelagic invertebrate prey communities. Here, we present notable trends in the availability of invertebrate prey at several sites within a restoring large river delta in Puget Sound, Washington, U.S.A. Three years after the system was returned to tidal influence, we observed substantial additions to amphipod, copepod, and cumacean abundances in newly accessible marsh channels (from 0 to roughly 5,000–75,000 individuals/m2). In the restoration area, terrestrial invertebrate colonization was dependent upon vegetative cover, with dipteran and hymenopteran biomass increasing 3‐fold between 1 and 3 years post‐restoration. While the overall biodiversity within the restoration area was lower than in the reference marsh, estimated biomass was comparable to or greater than that found within the other study sites. This additional prey biomass likely provided foraging benefits for juvenile Chinook, chum, and coho salmon. Primary physical drivers differed for benthic, terrestrial, and pelagic invertebrates, and these invertebrate communities are expected to respond differentially depending on organic matter exchange and vegetative colonization. Restoring estuaries may take decades to meet certain success criteria, but our study demonstrates rapid enhancements in foraging resources understood to be used for estuary‐dependent wildlife.

Functional diversity of the lateral line system among populations of a native Australian freshwater fish.

Fishes use their mechanoreceptive lateral line system to sense nearby objects by detecting slight fluctuations in hydrodynamic motion within their immediate environment. Species of fish from different habitats often display specialisations of the lateral line system, in particular the distribution and abundance of neuromasts, but the lateral line can also exhibit considerable diversity within a species. Here, we provide the first investigation of the lateral line system of the Australian western rainbowfish (Melanotaenia australis), a species that occupies a diversity of freshwater habitats across semi-arid northwest Australia. We collected 155 individuals from eight populations and surveyed each habitat for environmental factors that may contribute to lateral line specialisation, including water flow, predation risk, habitat structure and prey availability. Scanning electron microscopy and fluorescent dye labelling were used to describe the lateral line system in M. australis, and to examine whether the abundance and arrangement of superficial neuromasts (SNs) varied within and among populations. We found that the SNs of M. australis were present in distinct body regions rather than lines. The abundance of SNs within each body region was highly variable, and also differed among populations and individuals. Variation in SN abundance among populations was best explained by habitat structure and the availability of invertebrate prey. Our finding that specific environmental factors explain among-population variation in a key sensory system suggests that the ability to acquire sensory information is specialised for the particular behavioural needs of the animal.

Diel shifts in the structure and function of nearshore estuarine fish communities.

Day-night shifts in the nearshore fish fauna of a temperate microtidal estuary were assessed using a holistic suite of structural and functional community attributes. Mean fish species richness and diversity (taxonomic distinctness) were higher at night across all regions of the estuary and seasons, concurring with the findings of numerous comparable studies reviewed worldwide, while the diel period in which mean abundance was higher varied among seasons. Likewise, species and functional guild compositions (the latter based on feeding modes and habitat use) both differed significantly between day and night, with the extent of the diel shift again varying seasonally. Daytime fish communities were characterized by higher abundances of Atherinidae, Sillaginidae and Mugilidae, while Gobiidae were far more abundant at night. Marked shifts in size composition were also evident, with smaller fishes (<100 mm total length, LT ) being more prevalent during the day and larger fishes (≥200 mm LT ) proportionally more abundant at night. The above diel shifts were feasibly related to a range of predator-prey interactions and feeding-related movements, namely a nocturnal decrease in top-order avian piscivory coupled with an increase in invertebrate prey availability, resulting in changes in the presence and catchability of certain fish species in shallow estuarine waters.

Dancing in the moonlight: evidence that Killdeer foraging behaviour varies with the lunar cycle

Plovers (subfamily: Charadriinae) are visual foragers that rely on ambient light for detection of invertebrates, as demonstrated by their foot-stirring behaviour used to stimulate a flight response in prey. At night, although ambient light is minimal, predation pressure from diurnal raptors is reduced and invertebrate prey availability increases, thus creating fitness benefits to nocturnal foraging by invertivores. The Killdeer (Charadrius vociferus) is a widespread yet understudied Plover that primarily inhabits agricultural fields throughout North America during the winter. Because nocturnal ambient light is directly dependent upon the lunar cycle, I hypothesized that Killdeer exploit nights with greater lunar illumination to be able to forage when predation risk is low and prey availability is enhanced. I predicted that nocturnal activities by Killdeer would be reflected in their diurnal behaviour the subsequent day, with decreased diurnal foraging following lighter nights. I also considered the additive effect of lower ambient temperatures and precipitation. I used an information-theoretic framework to compare these hypotheses and found the model with greatest support revealed a clear negative relationship between diurnal foraging and the amount of lunar illumination the preceding night. Interestingly, I found the opposite trend in diurnal roosting behaviour, suggesting that if nocturnal light levels suffice, Killdeer forage at night and roost during the day. I propose that this behaviour is driven by differential predation risk and food availability perceived by Killdeer at night vs. day. I also discuss the potential functional importance of energetic demands. Taken together, these results highlight the potential for avian diurnal behaviour to be closely tied to natural variation in nocturnal light availability, a finding with potential relevance to the increasing threat of artificial light pollution in our era of industrialization.

Habitat Use and Foraging Patterns of Molting Male Long-tailed Ducks in Lagoons of the Central Beaufort Sea, Alaska

From mid-July through September, 10 000 to 30 000 Long-tailed Ducks (&lt;em&gt;Clangula hyemalis&lt;/em&gt;) use the lagoon systems of the central Beaufort Sea for remigial molt. Little is known about their foraging behavior and patterns of habitat use during this flightless period. We used radio transmitters to track male Long-tailed Ducks through the molt period from 2000 to 2002 in three lagoons: one adjacent to industrial oil field development and activity and two in areas without industrial activity. We found that an index to time spent foraging generally increased through the molt period. Foraging, habitat use, and home range size showed similar patterns, but those patterns were highly variable among lagoons and across years. Even with continuous daylight during the study period, birds tended to use offshore areas during the day for feeding and roosted in protected nearshore waters at night. We suspect that variability in behaviors associated with foraging, habitat use, and home range size are likely influenced by availability of invertebrate prey. Proximity to oil field activity did not appear to affect foraging behaviors of molting Long-tailed Ducks.

Feeding ecology and prey resource partitioning of lenok (Brachymystax lenok) and Baikal grayling (Thymallus arcticus baicalensis) in the Eg and Uur rivers, Mongolia

AbstractBaikal grayling (Thymallus arcticus baicalensis) and lenok (Brachymystax lenok) are two salmonids which co‐occur in lakes and rivers of the Selenga River and Lake Baikal drainage in northern Mongolia and Siberia. Populations of both species have declined due to habitat loss and overfishing. Previous studies have established that diets of both species are comprised of aquatic and terrestrial invertebrates, but none have examined how prey resources are partitioned between the species. We explored resource partitioning between these species using information from stomach content analysis and stable isotope analysis of carbon and nitrogen. Stomach content data were also compared to invertebrate prey availability estimated from drift and benthic samples. Stomach content analysis indicated that lenok were benthic specialists, while Baikal grayling exhibited a more generalised and surface‐oriented diet, preying upon both terrestrial and aquatic invertebrates. In addition, drifting invertebrate prey availability was positively related to diet overlap based on stomach content analysis, suggesting that competition was involved in the prey resource partitioning we observed. Our analysis of assimilated diet using stable isotopes was generally consistent with stomach contents, indicating that prey partitioning was sustained over a period of several months, but also revealed a greater importance of fish prey to lenok diets. This study provides a baseline description of prey utilisation and prey resource partitioning between lenok and Baikal grayling, which may be used to guide management and future research of these threatened species.

Invertebrate prey availability limits reproductive success but not breeding population size in suburban House Sparrows Passer domesticus

Factors affecting avian demography and abundance in urban landscapes are poorly understood and this hinders attempts to manage urban bird communities. Several recent studies indicate that lack of invertebrate prey in urban landscapes may constrain avian productivity and fitness relative to that in other habitats. House Sparrow Passer domesticus populations have undergone large declines in many European urban centres and inadequate reproductive success linked to invertebrate availability has been postulated as a potential cause of these declines. We conducted a replicated supplementary feeding experiment to test whether the availability of invertebrate prey limits the breeding success and adult abundance (colony size) of House Sparrows in suburban London, where House Sparrow populations declined by 60% during the decade preceding our study. Daily mealworm provision over two successive breeding seasons, sufficient to provide 82% of chick energy requirements of House Sparrow pairs nesting within 50 m of feeders, had a large positive impact on the abundance of recently fledged birds (+62%), but only a small positive impact, limited mainly to small colonies, on the overall abundance of territorial males. Colony growth was only weakly related to fledgling abundance in the previous year and did not appear to be constrained by nest‐site availability. Conservation interventions that enhance invertebrate availability for suburban House Sparrows may increase reproductive success but are unlikely, on their own, to lead to population growth or recovery.

Diet shifts by planktivorous and benthivorous fishes in northern Lake Michigan in response to ecosystem changes

In Lake Michigan, diets of planktivorous and benthivorous fishes have varied over the past decades, in part owing to food web changes. To update diet information and compare them to a similar effort in 1994–1995, we analyzed the diets of seven benthivorous and planktivorous fish species collected along two northern Lake Michigan transects that spanned nearshore (18 m), intermediate (46 m), and offshore (91, 110, 128 m) bottom depths during spring, summer, and autumn of 2010. Calanoid copepods (e.g., Limnocalanus macrurus, Leptodiaptomus sicilis, and Senecella calanoides) comprised a majority of the diets in at least one season for all sizes of alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), and rainbow smelt (Osmerus mordax). Similarly, Mysis diluviana was the highest proportion in at least one season for large sizes of alewife, bloater, and rainbow smelt, as well as slimy sculpin (Cottus cognatus) and deepwater sculpin (Myoxocephalus thompsonii). The diets of the remaining two species, ninespine stickleback (Pungitius pungitius) and round goby (Neogobius melanostomus), were dominated by herbivorous cladocerans or dreissenid mussels, respectively. Interspecific diet overlap was minimal at 18 and 46 m. In offshore waters, however, overlap was relatively high, driven by frequent consumption of Mysis. Relative to 1994–1995, 2010 diets revealed increased feeding on calanoid copepods and Mysis, with corresponding declining consumption of Diporeia spp. and herbivorous cladocerans. Relative diet weight was also higher in 1994–1995 than in 2010 for small and large bloater and both sculpin species. We hypothesize that the shifts in diets are reflective of community-level changes in invertebrate prey availability.