Prey Biomass Research Articles

Linking land cover satellite data with dietary variation and reproductive output in an opportunistic forager: Arable land use can boost an ontogenetic trophic bottleneck in the White Stork Ciconia ciconia

Determining how the progressive loss of resources due to agricultural intensification and habitat degradation affect individual fitness and population persistence is a matter of urgency. Here we explored three major questions in order to extend knowledge of the relationship between reproduction rate, diet and energy intake in White Storks Ciconia ciconia based both on our own analysis of pellets and landscape properties sampled in 52 nests in south-western Poland, and published literature data. (1) How many individual prey items are needed to meet the daily energy requirements of nestlings over the brood rearing period? (2) How do the dietary patterns vary under different habitat conditions and what is the spatial scale responsible for these relationships? (3) Is reproductive output related to variations in landscape traits, and is diet variability related to intraspecific competition resulting from colonial breeding? In our estimation, the energy requirements of nestlings during the brood rearing period showed that the most profitable invertebrate prey items were Orthoptera and earthworms. Owing to the nestlings' gape-size constraint (precluding consumption of vertebrate prey items of the size of Common Voles), these most likely comprise the staple diet enabling survival during the first 20 days of life. The total energy content across all the pellets was a simple function (a negative correlation) of %arable land within a distance of 5 km around the nests. White Storks from nests of high-productivity pairs (with 3–4 fledglings and less %arable around) consumed equal %biomasses of invertebrate and vertebrate prey, while invertebrates prevailed in the diet of the low-productivity pairs. Our results suggest that a two-level ontogenetic trophic bottleneck may explain the low productivity of White Stork pairs in simplified landscapes with predominant arable land use. As a result of this, parent birds are unable to satisfy the growing energy demands of nestlings (1) by gathering a sufficient volume of abundant small-sized prey (early nestlings) and (2) by delivering energetically more profitable vertebrate prey at the time of the diet switch.

Insectivorous birds consume an estimated 400\u2013500\xa0million\xa0tons of prey annually

In this paper, we present an estimate of the predation impact of the global population of insectivorous birds based on 103 (for the most part) published studies of prey consumption (kg ha−1 season−1) of insectivorous birds in seven biome types. By extrapolation—taking into account the global land cover of the various biomes—an estimate of the annual prey consumption of the world’s insectivorous birds was obtained. We estimate the prey biomass consumed by the world’s insectivorous birds to be somewhere between 400 and 500 million metric tons year−1, but most likely at the lower end of this range (corresponding to an energy consumption of ≈ 2.7 × 1018 J year−1 or ≈ 0.15% of the global terrestrial net primary production). Birds in forests account for > 70% of the global annual prey consumption of insectivorous birds (≥ 300 million tons year−1), whereas birds in other biomes (savannas and grasslands, croplands, deserts, and Arctic tundra) are less significant contributors (≥ 100 million tons year−1). Especially during the breeding season, when adult birds feed their nestlings protein-rich prey, large numbers of herbivorous insects (i.e., primarily in the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera) supplemented by spiders are captured. The estimates presented in this paper emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale—especially in forested areas.

Inducible defense destabilizes predator–prey dynamics: the importance of multiple predators

Phenotypic plasticity in prey can have a dramatic impact on predator–prey dynamics, e.g. by inducible defense against temporally varying levels of predation. Previous work has overwhelmingly shown that this effect is stabilizing: inducible defenses dampen the amplitudes of population oscillations or eliminate them altogether. However, such studies have neglected scenarios where being protected against one predator increases vulnerability to another (incompatible defense). Here we develop a model for such a scenario, using two distinct prey phenotypes and two predator species. Each prey phenotype is defended against one of the predators, and vulnerable to the other. In strong contrast with previous studies on the dynamic effects of plasticity involving a single predator, we find that increasing the level of plasticity consistently destabilizes the system, as measured by the amplitude of oscillations and the coefficients of variation of both total prey and total predator biomasses. We explain this unexpected and seemingly counterintuitive result by showing that plasticity causes synchronization between the two prey phenotypes (and, through this, between the predators), thus increasing the temporal variability in biomass dynamics. These results challenge the common view that plasticity should always have a stabilizing effect on biomass dynamics: adding a single predator–prey interaction to an established model structure gives rise to a system where different mechanisms may be at play, leading to dramatically different outcomes.

The diet of a declining Red-billed Chough Pyrrhocorax pyrrhocorax population on Islay, Scotland

ABSTRACTCapsule: We quantify Red-billed Chough Pyrrhocorax pyrrhocorax diet from faecal samples collected on Islay. Dung invertebrates formed the majority of prey biomass in dune pasture and Tipulid larvae in mixed pasture but Aphodius larvae were scarce in the diet, whereas they had been a major component in the 1980s. There are management implications from the indication of a reduction in availability of preferred food.

Agroecological farming practices promote bats

Intensive agriculture is a major driver of biodiversity loss, and a critical part of creating sustainable food systems is finding ways to balance production and conservation. While practices characteristic of agricultural intensification tend to erode biodiversity, agroecological farming practices can potentially support biodiversity and enhance pest suppression services. Bats are important predators of agricultural pests, yet little is known about how prescriptive management practices can be used to support bats and their associated pest-suppression services. We investigate how bats use natural habitat and conventional and organic farms in an agricultural landscape, ask which on-farm management practices may benefit bats, and examine how these management practices influence bats by mediating changes in habitat quality. We conducted acoustic surveys at 54 sites in the California Central Coast Region, a productive region with high ecological and economic value. We found higher bat activity in natural habitat compared to farms for total bat activity and clutter-adapted, but not open space bats, and slightly higher bat diversity in natural habitat compared to conventional farms. We found no effect of habitat type on species richness and a weak effect of habitat type on bat diversity, although bat community composition differed significantly between natural habitat and farms. Crop diversification increased the activity of all bat species and clutter-adapted, but not open space bats, regardless of the amount of semi-natural habitat surrounding farms. Both crop diversification and less frequent pesticide applications increased prey biomass, and the activity of clutter-adapted bats was positively correlated with greater Lepidoptera biomass. We suggest that improving habitat quality (increasing abundance of insect prey) through vegetative diversification and/or less frequent pesticide applications offers flexible management options to growers by considering both bat ecology and the constraints of regional agricultural management practices.

Brood provisioning and reproductive benefits in relation to habitat quality: a food supplementation experiment

Food availability is a major characteristic of habitat quality, linking habitats with demographic parameters such as reproductive performance. Parent birds adjust their food provisioning to both habitat-specific food characteristics and the demands of their young. However, because habitat quality and the brood's food intake are often correlated, the underlying mechanisms of adjustments in parental provisioning remain entangled. How the relationship between habitat quality and parental provisioning behaviour affects the quantity of food available to nestlings and the resulting nestling growth and survival is therefore still incompletely established. We experimentally increased the food intake of little owl, Athene noctua, nestlings in two habitat types differing in food availability and used unsupplemented broods as controls. The food supplementation experiment allowed us to disentangle the effect of habitat type from the effect of the nestlings' food intake on parental provisioning behaviour. Camera traps recording a series of 10 consecutive images for each parental visit allowed us to quantify visiting rates and diet composition by applying a hierarchical multinomial model explicitly accounting for the observation process. Food supplementation caused parents to switch to smaller food items and to increase visiting rates, resulting in similar biomass brought to nestlings in supplemented and unsupplemented broods. Irrespective of the food supplementation, parents in low-quality habitats delivered 63% of the biomass delivered by those in high-quality habitats. Accordingly, we found an increase in nestling survival rates in response to food supplementation in low-quality habitats, but not in high-quality habitats. Our results show that habitat quality affects the biomass of prey delivered to the brood, whereas the nutritional state of the brood affects prey selection or foraging modes of parents. Reproductive output directly reflected habitat quality in terms of food availability, identifying food as the main factor underlying differential reproduction within and between populations.

Functional traits and environmental conditions predict community isotopic niches and energy pathways across spatial scales

Abstract Despite ongoing research in food web ecology and functional biogeography, the links between food web structure, functional traits and environmental conditions across spatial scales remain poorly understood. Trophic niches, defined as the amount of energy and elemental space occupied by species and food webs, may help bridge this divide. Here, we ask how the functional traits of species, the environmental conditions of habitats and the spatial scale of analysis jointly determine the characteristics of trophic niches. We used isotopic niches as a proxy of trophic niches, and conducted analyses at spatial scales ranging from local food webs and metacommunities to geographically distant sites. We sampled aquatic macroinvertebrates from 104 tank bromeliads distributed across five sites from Central to South America and compiled the macroinvertebrates’ functional traits and stable isotope values (δ15N and δ13C). We assessed how isotopic niches within each bromeliad were influenced by the functional trait composition of their associated invertebrates and environmental conditions (i.e., habitat size, canopy cover [CC] and detrital concentration [DC]). We then evaluated whether the diet of dominant predators and, consequently, energy pathways within food webs reflected functional and environmental changes among bromeliads across sites. At last, we determined the extent to which the isotopic niches of macroinvertebrates within each bromeliad contributed to the metacommunity isotopic niches within each site and compared these metacommunity‐level niches over biogeographic scales. At the bromeliad level, isotopic niches increased with the functional richness of species in the food web and the DC in the bromeliad. The diet of top predators tracked shifts in prey biomass along gradients of CC and DC. Bromeliads that grew under heterogeneous CC displayed less trophic redundancy and therefore combined to form larger metacommunity isotopic niches. At last, the size of metacommunity niches depended on within‐site heterogeneity in CC. Our results suggest that the trophic niches occupied by food webs can predictably scale from local food webs to metacommunities to biogeographic regions. This scaling process is determined by both the functional traits of species and heterogeneity in environmental conditions. A plain language summary is available for this article.

Have Invasive Mysids (Mysis diluviana) Altered the Capacity of Osoyoos Lake, British Columbia to Produce Sockeye Salmon (Oncorhynchus nerka)?

Background:During 2005-13, at Osoyoos Lake, British Columbia, we investigated trophic relationships among fry ofOncorhynchus nerkaWalbaum (Sockeye and kokanee), a suite of limnetic planktivores includingMysis diluviana, and their zooplankton prey.Objectives:Our goal was to quantify the impacts that a recently introduced population ofMysiswould have on density, growth and survival of resident age-0 Sockeye Salmon.Methods:Evidence ofMysisimpact was based on (a) simple correlation analysis between various biophysical performance measures and (b) production and bioenergetics models used to identify the strength of bottom-up (i.e. production-driven) and top-down (i.e.consumption-driven) processes.Results:This nine-year study indicated that the Osoyoos Lake food web was strongly influenced by external events These included: large annual variations in river discharge, an earthen dam failure and effluent input from an Okanagan River tributary, and highly variable recruitment ofO. nerkafry given out-of-basin factors (harvest, marine survival) controlling adult salmon returns. Surprisingly, large annual variations inO. nerkarecruitment (0.63 - 7.0 million fry), did not induce significant “top-down” associations in growth, survival or subsequent production among the macro-planktivores (pelagic fish andMysis) and their zooplankton prey. A single significant correlation (p ≤ 0.05) betweenO. nerkafry abundance and their von BertalanffyW∞parameter emerged from a set of 14 potential top-down associations tested. By contrast, we identified several strongly positive “bottom-up” effects in which survival ofO. nerkafry was significantly associated (p ≤ 0.01) with annual variations in total zooplankton biomass,Daphniabiomass andEpischurabiomass. Our results indicate thatMysisplayed a dual role in the Osoyoos Lake pelagic food web. As predators, they accounted for an average (June-October) of 64% of the total prey biomass consumed by fish andMysis. As prey,Mysiscontributed an average of 35% of the prey biomass consumed by fish. Consumption by fish andMysistogether accounted for daily losses of only 4.5% of non-mysid zooplankton biomass and 34% of daily zooplankton production.Conclusion:We conclude that in all years, combined prey consumption byMysisand fish was never high enough, acting alone, to reduce the availability of their potential zooplankton forage base. However, we also estimate that in the absence ofMysis,O. nerkafry could experience a 43% increase in their daily food intake and that fish andMysismight control their principal prey taxa when exogenous factors (e.g.annual discharge) induced major reductions in zooplankton biomass. Finally, althoughMysishas clearly altered the energy flow pathways from plankton to fish in the Osoyoos Lake food-web, mysids have not precluded rebuildingO. nerkaabundance to levels at or exceeding historic maxima.

Spatial and temporal patterns in the diet of barn owl (Tyto alba) in Cyprus

BackgroundThe barn owl, a nocturnal raptor with cosmopolitan distribution, shows a great adaptability to different environments. Regarding prey, the barn owl is a rather selective species, but if changes in the abundance of the selected prey occur, it becomes an opportunistic predator and easily incorporates other prey in its diet, using a wide range of prey species and foraging habitats. Small rodents are usually the prey mostly used. Compared to the populations of north and eastern Europe, barn owl populations in the Mediterranean area have been the least studied. In Cyprus, where barn owl is a common bird species, there are no studies on its diet and feeding ecology. This study was carried out to contribute to the spatial and temporal patterns barn owl diet in Cyprus also providing information on small mammals’ presence and species composition on the island.MethodsThis study was based on 1407 regurgitated pellet analysis that were collected from 26 sites representing six major habitat types on central and southern Cyprus from summer 2013 to summer 2014. The diet of the barn owl was described in terms of seasonal average biomass and numerical percentages of each prey species and compared by Kruskal–Wallis test. Seasonal prey diversity and evenness indices were also calculated. Principal component analysis (PCA) was performed on the prey biomass proportion data assigned to six major habitat types with regard to elevation, vegetation and human uses.ResultsLow prey diversity was found comprised mainly of rodents (overall means 96.2 and 95.7% by number and biomass, respectively). Mice followed by rats were most important prey whereas insectivores, birds and insects were minor components of the owl’s diet. Evenness and diversity values were relatively similar among seasons. PCA differentiated mainly between lowland areas where mice were more abundant prey and mountainous areas where rats dominated in the diet. Insectivores correlated with birds, prey types characterizing several lowland and highland habitats.ConclusionsThe barn owl prey composition in Cyprus suggests an opportunistic foraging behavior, low prey species diversity with variations in the main rodent prey that could be explained by their distribution, seasonal activity and habitat preferences.

Caught in the web: Spider web architecture affects prey specialization and spider-prey stoichiometric relationships.

Quantitative approaches to predator–prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator–prey interactions. Here, we used spider–prey interactions as a model system to investigate whether different spider web architectures—orb, tangle, and sheet‐tangle—affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle‐web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet‐tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle‐web spiders than for orb and sheet‐tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator–prey interactions.

Temporal changes in prey composition and biomass delivery to African Crowned Eagle nestlings in urban areas of KwaZulu-Natal, South Africa

Globally urban areas are expanding rapidly and this usually has negative effects on biodiversity. Despite this, some species manage to persist in urban areas, as is the case with African Crowned Eagles Stephanoaetus coronatus in KwaZulu-Natal, South Africa. As relatively little is known about African Crowned Eagle nestling diet, especially about how it changes with nestling age, we investigated this with nest camera-traps. We analysed temporal changes in prey composition and biomass delivery during the nestling stage. We also recorded which adults provisioned and attended the nest. The main prey fed to nestlings were Rock Hyrax Procavia capensis and Hadeda Ibis Bostrychia hagedash. Adult males did most of the food provisioning, especially at the start of the nestling period. We found a decrease in total prey number and biomass with nestling age. This may be caused by changing requirements of nestlings. Furthermore, delivering fewer prey at later nestling stages may be a facilitating mechanism to enhance fledging of the nestling. Although the total number of prey brought to the nest decreased, we found an increase in numbers of Vervet Monkey Chlorocebus pygerythrus in the diet with nestling age. This indicated an increase in larger prey being delivered to the nests as the nestling aged. We suggest that this could be caused by increased participation in hunting by the larger female as her nest attendance time decreased as the nestling aged. We conclude with emphasising the importance of protecting the Durban Metropolitan Open Space System (D’MOSS) zones for the persistence of this Near Threatened raptor species, and populations of its prey in urban areas for its breeding success.

Reversed predator-prey cycles are driven by the amplitude of prey oscillations.

Ecoevolutionary feedbacks in predator–prey systems have been shown to qualitatively alter predator–prey dynamics. As a striking example, defense–offense coevolution can reverse predator–prey cycles, so predator peaks precede prey peaks rather than vice versa. However, this has only rarely been shown in either model studies or empirical systems. Here, we investigate whether this rarity is a fundamental feature of reversed cycles by exploring under which conditions they should be found. For this, we first identify potential conditions and parameter ranges most likely to result in reversed cycles by developing a new measure, the effective prey biomass, which combines prey biomass with prey and predator traits, and represents the prey biomass as perceived by the predator. We show that predator dynamics always follow the dynamics of the effective prey biomass with a classic ¼‐phase lag. From this key insight, it follows that in reversed cycles (i.e., ¾‐lag), the dynamics of the actual and the effective prey biomass must be in antiphase with each other, that is, the effective prey biomass must be highest when actual prey biomass is lowest, and vice versa. Based on this, we predict that reversed cycles should be found mainly when oscillations in actual prey biomass are small and thus have limited impact on the dynamics of the effective prey biomass, which are mainly driven by trait changes. We then confirm this prediction using numerical simulations of a coevolutionary predator–prey system, varying the amplitude of the oscillations in prey biomass: Reversed cycles are consistently associated with regions of parameter space leading to small‐amplitude prey oscillations, offering a specific and highly testable prediction for conditions under which reversed cycles should occur in natural systems.

Tiger and leopard diets in western Thailand: Evidence for overlap and potential consequences

Interference competition by tigers, Panthera tigris, is widely reported to reduce leopard, Panthera pardus, density or cause its shift to more a marginal habitat. In Southeast Asia, lack of a medium sized prey, spotted deer (Axis axis), and increased consumption of sambar (Rusa unicolor) by leopards amplifies dietary overlap between these two large felids. In our study area in western Thailand, leopard density was 2.4 times that of tigers. Using scat analysis we estimated prey biomass in the diet of each species to examine resource competition between these species. Tigers had a 0.89 spatial overlap with leopards and leopards a 0.92 overlap with tigers. Larger prey in this system (>100 kg) composed 89.8 Ackerman's coefficient, ACF, and 79.3% Chakrabati's coefficient, CCF of the biomass in tiger diet and 47.0% (ACF) and 45.3% (CCF) of the biomass in leopard diet. Dietary overlap of prey >100 kg versus smaller prey (≤37 kg) between these felids was 74.4% (ACF) and 81.2% (CCF). Dense cover at our site may reduce interference competition from tigers. In turn, high leopard density and leopard consumption of young sambar likely increases resource competition with tigers and thus potentially reduces tiger density. Given current small tiger population sizes, it is important to recognize that leopards may compete with and potentially suppress tiger numbers at some locations throughout their range and this topic needs further study.

Predator and prey biodiversity relationship and its consequences on marine ecosystem functioning-interplay between nanoflagellates and bacterioplankton.

The importance of biodiversity effects on ecosystem functioning across trophic levels, especially via predatory-prey interactions, is receiving increased recognition. However, this topic has rarely been explored for marine microbes, even though microbial biodiversity contributes significantly to marine ecosystem function and energy flows. Here we examined diversity and biomass of bacteria (prey) and nanoflagellates (predators), as well as their effects on trophic transfer efficiency in the East China Sea. Specifically, we investigated: (i) predator diversity effects on prey biomass and trophic transfer efficiency (using the biomass ratio of predator/prey as a proxy), (ii) prey diversity effects on predator biomass and trophic transfer efficiency, and (iii) the relationship between predator and prey diversity. We found higher prey diversity enhanced both diversity and biomass of predators, as well as trophic transfer efficiency, which may arise from more balanced diet and/or enhanced niche complementarity owing to higher prey diversity. By contrast, no clear effect was detected for predator diversity on prey biomass and transfer efficiency. Notably, we found prey diversity effects on predator-prey interactions; whereas, we found no significant diversity effect on biomass within the same trophic level. Our findings highlight the importance of considering multi-trophic biodiversity effects on ecosystem functioning in natural ecosystems.

Feeding ecology of invasive lionfish (Pterois volitans and Pterois miles) in the temperate and tropical western Atlantic

Numerous location-based diet studies have been published describing different aspects of invasive lionfish (Pterois volitans and Pterois miles) feeding ecology, but there has been no synthesis of their diet composition and feeding patterns across regional gradients. 8125 lionfish stomachs collected from 10 locations were analyzed to provide a generalized description of their feeding ecology at a regional scale and to compare their diet among locations. Our regional data indicate lionfish in the western Atlantic are opportunistic generalist carnivores that consume at least 167 vertebrate and invertebrate prey species across multiple trophic guilds, and carnivorous fish and shrimp prey that are not managed fishery species and not considered at risk of extinction by the International Union for Conservation of Nature disproportionately dominate their diet. Correlations between lionfish size and their diet composition indicate lionfish in the western Atlantic transition from a shrimp-dominated diet to a fish-dominated diet through ontogeny. Lionfish total length (TL) (mm) was found to predict mean prey mass per stomach (g) by the following equation mean prey mass =0.0002*TL1.6391, which can be used to estimate prey biomass consumption from lionfish length-frequency data. Our locational comparisons indicate lionfish diet varies considerably among locations, even at the group (e.g., crab) and trophic guild levels. The Modified Index of Relative Importance developed specifically for this study, calculated as the frequency of prey a × the number of prey a, can be used in other diet studies to assess prey importance when prey mass data are not available. Researchers and managers can use the diet data presented in this study to make inference about lionfish feeding ecology in areas where their diet has yet to be described. These data can be used to guide research and monitoring efforts, and can be used in modeling exercises to simulate the potential effects of lionfish on marine food webs. Given the large variability in lionfish diet composition among locations, this study highlights the importance of continued location-based diet assessments to better inform local management activities.

Acoustic backscatter at a Red Sea whale shark aggregation site

An aggregation of sexually immature whale sharks occurs at a coastal submerged reef near the Saudi Arabian Red Sea coast each spring. We tested the hypothesis that these megaplanktivores become attracted to a prey biomass peak coinciding with their aggregation. Acoustic backscatter of the water column at 120 kHz and 333 kHz –a proxy for potential prey biomass – was continuously measured spanning the period prior to, during, and subsequent to the seasonal whale shark aggregations. No peak in acoustic backscatter was observed at the time of the aggregation. However, we observed a decrease in acoustic backscatter in the last days of deployment, which coincided the trailing end of whale shark season. Organisms forming the main scattering layer performed inverse diel vertical migration, with backscatter peaking at mid-depths during the day and in the deeper half of the water column at night. Target strength analyses suggested the backscatter was likely composed of fish larvae. Subsurface foraging behavior of the whale sharks within this aggregation has not been described, yet this study does not support the hypothesis that seasonal peaks in local whale shark abundance correspond to similar peaks in prey availability.

Avian predator buffers against variability in marine habitats with flexible foraging behavior

How well seabirds compensate for variability in prey abundance and composition near their breeding colonies influences their distribution and reproductive success. We used tufted puffins (Fratercula cirrhata) as forage fish samplers to study marine food webs from the western Aleutian Islands (53°N, 173°E) to Kodiak Island (57°N, 153°W), Alaska, during August 2012–2014. Around each colony we obtained data on: environmental characteristics (sea surface temperature and salinity, seafloor depth and slope, tidal range, and chlorophyll-a), relative forage fish biomass (hydroacoustic backscatter), and seabird community composition and density at-sea. On colonies, we collected puffin chick-meals to characterize forage communities and determine meal energy density, and measured chicks to obtain a body condition index. There were distinct environmental gradients from west to east, and environmental variables differed by ecoregions: the (1) Western-Central Aleutians, (2) Eastern Aleutians, and, (3) Alaska Peninsula. Forage fish biomass, species richness, and community composition all differed markedly between ecoregions. Forage biomass was strongly correlated with environmental gradients, and environmental gradients and forage biomass accounted for ~ 50% of the variability in at-sea density of tufted puffins and all seabird taxa combined. Despite the local and regional variability in marine environments and forage, the mean biomass of prey delivered to puffin chicks did not differ significantly between ecoregions, nor did chick condition or puffin density at-sea. We conclude that puffins can adjust their foraging behavior to produce healthy chicks across a wide range of environmental conditions. This extraordinary flexibility enables their overall success and wide distribution across the North Pacific Ocean.

Proximity of breeding and foraging areas affects foraging effort of a crepuscular, insectivorous bird

When complementary resources are required for an optimal life cycle, most animals need to move between different habitats. However, the level of connectivity between resources can vary and, hence, influence individuals’ behaviour. We show that landscape composition and configuration affect the connectivity between breeding (heathlands) and foraging habitats (extensively-grazed grasslands) of the European Nightjar (Caprimulgus europaeus), a crepuscular insectivorous bird. On a daily basis, nightjars connect breeding and foraging sites by rapidly crossing unsuitable habitats in order to exploit a higher prey biomass in foraging sites. However, low availability of foraging habitat near breeding sites and clustered landscapes greatly increase foraging distance. Birds occupying these sub-optimal breeding areas compensate for longer travels by increasing foraging duration, and their physiology shows increased stress levels. All findings suggest that landscape heterogeneity can affect population dynamics of nightjars. Therefore, we recommend an integrated management approach for this EU-protected bird species.

Relationships between indicators of acid-base chemistry and fish assemblages in streams of the Great Smoky Mountains National Park

The acidity of many streams in the Great Smoky Mountains National Park (GRSM) has increased significantly since pre-industrial (∼1850) times due to the effects of highly acidic atmospheric deposition in poorly buffered watersheds. Extensive stream-monitoring programs since 1993 have shown that fish and macroinvertebrate assemblages have been adversely affected in many streams across the GRSM. Matching chemistry and fishery information collected from 389 surveys performed at 52 stream sites over a 22-year period were assessed using logistic regression analysis to help inform the U.S. Environmental Protection Agency’s assessment of the environmental impacts of emissions of oxides of nitrogen (NOx) and sulfur (SOx). Numerous logistic equations and associated curves were derived that defined the relations between acid neutralizing capacity (ANC) or pH and different levels of community richness, density, and biomass; and density and biomass of brook trout, rainbow trout, and small prey (minnow) populations in streams of the GRSM. The equations and curves describe the status of fish assemblages in the GRSM under contemporary emission levels and deposition loads of nitrogen (N) and sulfur (S) and provide a means to estimate how newly proposed (and various alternative) target deposition loads, which strongly influence stream ANC, might affect key ecological indicators. Several examples using ANC, community richness, and brook trout density are presented to illustrate the steps needed to predict how future changes in stream chemistry (resulting from different target deposition loads of N and S) will affect the probabilities of observing specific levels of selected biological indicators in GRSM streams. The implications of this study to the regulation of NOx and SOx emissions, water quality, and fisheries management in streams of the GRSM are discussed, but also qualified by the fact that specific examples provided need to be further explored before recommendations concerning their use as ecological indicators could be proposed.

The importance of fine-scale breeding site selection patterns under a landscape-sharing approach for wolf conservation

For large carnivores persisting in human-dominated landscapes, conservation planning is often hindered by the large spatial requirements of these species, availability of protected areas, and human land uses. Protected areas are usually too small to support viable populations, and scattered across a human land-use matrix. Therefore, large carnivore conservation should be planned at large spatial scales under a land-sharing approach (allowing the coexistence between large carnivores and people in the same landscape), which means increasing the focus on the human-dominated matrix. Most of the critical factors determining large carnivore persistence (i.e., those related to food availability and vulnerability to humans) interact synergistically in space and time during the breeding season. Here, using as a case study a wolf population in NW Iberia, we studied fine-scale breeding site selection patterns (1 and 9 km2) in relation to human pressure, and the availability of food and refuge. The selection of wolf breeding sites in this human-dominated landscape was not determined by potential availability of prey biomass in the immediate vicinity (1 km2). However, wolves selected breeding sites with high availability of refuge (concealing vegetation), and low human accessibility and activity levels. Paved roads showed the highest proportion of independent contribution to explaining breeding site selection patterns (negative influence), being followed by refuge availability (positive influence) and the remoteness of breeding sites in relation to the surrounding spatial context (positive influence). Refuge availability, even at very small spatial scales taking into account the spatial requirements of wolves, may compensate for moderate levels of human activities in the vicinity of breeding sites. The strength of breeding selection patterns varied along a hierarchical process at different spatial scales. Under a landscape-sharing approach, integrating key processes observed in the human-dominated matrix, such as breeding site selection patterns, into landscape planning is of paramount importance for carnivore conservation. By temporally restricting human use on breeding sites and small portions of surrounding lands (~ 1 km2), and by maintaining several small refuge areas interspersed within the human-dominated matrix, we could favor wolf persistence without reducing land availability for other uses, improving the conditions for coexistence between wolves and humans.