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The extent to which persisting species may fill the functional role of extirpated or declining species has profound implications for the structure of biological communities and ecosystem functioning. In North America, arthropodivorous bats are threatened on a continent‐wide scale by the spread of white‐nose syndrome (WNS), a disease caused by the fungus Pseudogymnoascus destructans. We tested whether bat species that display lower mortality from this disease can partially fill the functional role of other bat species experiencing population declines. Specifically, we performed high‐throughput amplicon sequencing of guano from two generalist predators: the little brown bat (Myotis lucifugus) and big brown bat (Eptesicus fuscus). We then compared changes in prey consumption before versus after population declines related to WNS. Dietary niches contracted for both species after large and abrupt declines in little brown bats and smaller declines in big brown bats, but interspecific dietary overlap did not change. Furthermore, the incidence and taxonomic richness of agricultural pest taxa detected in diet samples decreased following bat population declines. Our results suggest that persisting generalist predators do not necessarily expand their dietary niches following population declines in other predators, providing further evidence that the functional roles of different generalist predators are ecologically distinct. [ABSTRACT FROM AUTHOR]

Disturbances have long been recognized as important forces for structuring natural communities but their effects on trophic structure are not well understood, particularly in terrestrial systems. This is in part because quantifying trophic linkages is a challenge, especially for small organisms with cryptic feeding behaviors such as insects, and often relies on conducting labor‐intensive feeding trials or extensive observations in the field. In this study, we used stable isotopes of carbon and nitrogen to examine how disturbance (annual biomass harvesting) in tallgrass prairies affected the trophic position, trophic range, and niche space of ants, a widespread grassland consumer. We hypothesized that biomass harvest would remove important food and nesting resources of insects thus affecting ant feeding relationships and trophic structure. We found shifts in the feeding relationships inferred by isotopic signatures with harvest. In particular, these shifts suggest that ants within harvest sites utilized resources at lower trophic levels (possibly plant‐based resources or herbivores), expanded trophic breadth, and occupied different niche spaces. Shifts in resource use following harvest could be due to harvest‐mediated changes in both the plant and arthropod communities that might affect the strength of competition or alter plant nitrogen availability. Because shifts in resource use alter the flow of nutrients across the food web, disturbance effects on ants could have ecosystem‐level consequences through nutrient cycling. [ABSTRACT FROM AUTHOR]

Allochthonous resource movement across ecosystem boundaries creates episodic linkages between ecosystems. The sensitivity of the community to external resources of varying duration can alter the baseline upon which future pulses of allochthony can act. We explored the terrestrial ecosystem response to pulsed inputs of lake-derived resources with a manipulative experiment in a subarctic heathland where we assessed plant community and nutrient availability responses to additions of midge carcasses (Diptera: Chironomidae). Insect carcasses were added as either a one-time pulse or a 4-yr press to simulate differing durations of allochthony, which is common in the area. We found that midge pulses significantly elevated soil inorganic [N] in the first year (7× over background levels) but were significantly diminished (1.5×) by the second year after the initial pulse. The press treatment continued to elevate total soil inorganic [N] to 13× over background levels by the fourth year of midge additions, but then declined to 3.6× background in year 5 when experimental midge additions had ceased. In contrast to the soil inorganic N response, plant biomass was similar in pulse-addition and control plots over the course of the experiment. However, by the second year of the study plant biomass in press-addition plots were significantly higher than controls (>50%), and continued to increase over the 4 yr of the press treatment. Midge addition stimulated dominance of graminoids and thatch litter in plots that had previously been primarily heathland vegetation, a response that persisted 4 yr post-midge addition. Our findings suggest that soil and plant community responses to persistent insect carcass deposition (e.g., press) into heathland vegetation has the potential to carry forward in a way that modifies the baseline ecosystem conditions upon which additional allochthony may act. [ABSTRACT FROM AUTHOR]

Aquatic insects link adjacent ecosystems by transporting nutrients, energy, and material as they move from bodies of water into terrestrial habitats. Insects emerging from streams and rivers are known to benefit arthropod predators such as spiders, but their influence may extend to other arthropod feeding groups as well. We conducted a terrestrial arthropod survey at a series of lakes spanning a strong gradient of midge (Chironomidae, Diptera) emergence. These small, short-lived insects reach high densities in some areas such that their carcasses litter the ground, and serve as a potential resource for non-predatory arthropods. Our study revealed that arthropod assemblages in areas of high midge density were significantly different from those with few midges, the result of an increase of all taxa rather than changes in taxonomic composition. Eight of nine terrestrial arthropod taxa sampled showed a strong positive response to the presence of midges including detritivores and herbivores in addition to predators. Taxa that could consume living or dead midges directly responded especially strongly to midge gradients. Our results strongly suggest that midges enter the terrestrial arthropod food web through multiple pathways, increasing numbers of a wide range of arthropods. Furthermore, they emphasize the importance of lakes as sources of aquatic insects that significantly alter processes in the neighboring terrestrial environment. [ABSTRACT FROM AUTHOR]

Ecologists are increasingly interested in how disjunct habitats are connected through the cross-habitat movement of matter, prey, nutrients, and detritus and the implications for recipient systems. The study of lake ecosystems has been dominated by the study of pelagic (open-water) production and processes, though there is growing awareness of the role of terrestrial inputs and benthic trophic pathways. Here, we review the phenomena of airborne fluxes to and from lakes. We assemble published data on terrestrial particulate organic carbon (TPOC) deposition to lakes, insect production, and insect emergence and use these data to simulate how airborne lake-to-land and land-to-lake carbon flux is expected to scale with ecosystem size, while taking into account among-lake variability in emergence and TPOC deposition. Emergent insect flux to land increases as a function of lake size, while TPOC deposition to lakes decreases as a function of lake size. TPOC deposition exceeds insect emergence in small lakes, while in large lakes, insect emergence exceeds TPOC deposition. We present a general framework for considering directional fluxes across habitat boundaries. Furthermore, our results highlight the overarching role of ecosystem geometry in determining insect emergence, airborne carbon deposition, and net carbon flux between adjacent ecosystems. Les écologistes sont de plus en plus intéressés à savoir comment les habitats séparés sont reliés par des mouvements croisés de la matière, des proies, des nutriments et du détritus entre les habitats et aussi à en connaître les conséquences sur les systèmes récipiendaires. L'étude des écosystèmes lacustres a été dominée par la détermination de la production et des processus pélagiques (en eau libre), bien qu'il y ait une perception croissante du rôle des apports terrestres et des voies trophiques benthiques. Nous faisons une rétrospective du phénomène des flux atmosphériques provenant des lacs et y aboutissant. Nous rassemblons les données publiées sur les précipitations de carbone organique particulaire terrestre (TPOC) dans les lacs, sur la production des insectes et sur l'émergence des insectes et nous utilisons ces données pour simuler comment les flux atmosphériques de carbone du lac vers le milieu terrestre et du milieu terrestre vers le lac sont fonction de la taille de l'écosystème, tout en tenant compte de la variabilité de l'émergence et des précipitations de TPOC entre les lacs. Le flux d'insectes émergés vers le milieu terrestre augmente en fonction de la taille du lac, alors que les précipitations de TPOC dans les lacs diminuent en fonction de la taille du lac. Les précipitations de TPOC sont supérieures à l'émergence des insectes dans les petits lacs, alors que, dans les grands lacs, l'émergence des insectes dépasse les précipitations de TPOC. Nous présentons un cadre général pour l'étude des flux directionnels à travers les frontières des habitats. De plus, nos résultats soulignent le rôle prédominant de la géométrie de l'écosystème dans la détermination de l'émergence des insectes, des précipitations atmosphériques de carbone et du flux net de carbone entre les écosystèmes adjacents. [ABSTRACT FROM AUTHOR]

Abstract: Agri-environmental schemes (AES) are hypothesized to enhance biodiversity and ecosystem services in agroecosystems. We investigated how non-crop habitats in one AES influence seed-eating ground beetles (Coleoptera: Carabidae) and post-dispersal weed seed predation, an ecosystem service provided by these beetles. We found that the abundance of beetles was higher in the non-crop habitats than within the crop fields. Species diversity (measured by Simpson''s D), however, was greater in crop fields than in non-crop habitats. In addition, beetle assemblages were distinct between the crop and non-crop habitats possibly due to differences in the frequency and intensity of disturbance between crop and non-crop habitats. Seed predation by small predators (mainly ground beetles) was greater in the non-crop habitat than within the potato field. Moreover, we found a positive association between seed predation and beetle diversity both within the crop and in the non-crop habitat which provides evidence of a relationship between biodiversity and ecosystem services. Yet, differences in species assemblages suggest that species identity also affects rates of seed predation. [Copyright &y& Elsevier]

Recently, food web studies have started exploring how resources from one habitat or ecosystem influence trophic interactions in a recipient ecosystem. Benthic production in lakes and streams can be exported to terrestrial habitats via emerging aquatic insects and can therefore link aquatic and terrestrial ecosystems. In this study, we develop a general conceptual model that highlights zoobenthic production, insect emergence, and ecosystem geometry (driven principally by area-to-edge ratio) as important factors modulating the flux of aquatic production across the ecosystem boundary. Emerging insect flux, defined as total insect production emerging per meter of shoreline (g C·m-1·yr-1) is then distributed inland using decay functions and is used to estimate insect deposition rate to terrestrial habitats (g C·m-2yr-1). Using empirical data from the literature, we simulate insect fluxes across the water-land ecosystem boundary to estimate the distribution of fluxes and insect deposition inland for lakes and streams. In general, zoobenthos in streams are more productive than in lakes (6.67 vs. 1.46 g C·m-2yr-1) but have lower insect emergence to aquatic production ratios (0.19 vs. 0.30). However, as stream width is on average smaller than lake radius, this results in flux (F) estimates 2 Y2 times greater for lakes than for streams. Ultimately, insect deposition onto land (within 100 m of shore) adjacent to average-sized lakes (10-ha lakes, 0.021 g C·m-2yr-1) is greaterthan for average-sized streams (4 m width, 0.002 g C·m-2yr-1) used in our comparisons. For the average lake (both in size and productivity), insect deposition rate approaches estimates of terrestrial secondary production in low-productivity ecosystems (e.g., deserts and tundra, ≈0.07 g C·m-2yr-1). However, larger lakes (1300 ha) and streams (16 m) can have average insect deposition rates ,(≈0.01-2.4 g C·m-2yr-1) comparable to estimates of secondary production of more productive ecosystems such as grasslands. Because of the potentially large inputs of emerging aquatic insects intoterrestrial habitats, ecosystem processes and terrestrial consumers can be influenced by insect inputs. The relative contribution of lakes and streams to this flux will vary among landscapes depending on the number and size of these ecosystems types on the landscape. [ABSTRACT FROM AUTHOR]

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plantPhragmites australisand if the restoration of the native vegetation in brackishSpartina alternifloramarshes results in the reestablishment of the arthropod community. The invasion ofPhragmitesinto a coastalSpartinamarsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free-living specialists (e.g., planthoppers) inSpartinato concealed feeders inPhragmites(stem-feeding cecidomyiids). Moreover, free-living arthropods inPhragmitesbecame dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web-building linyphiids, were significantly reduced inPhragmiteshabitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages inPhragmites, as seen in the large shifts in feeding guilds, was significantly different from that inSpartina. Removal ofPhragmiteswith the herbicide glyphosate resulted in the rapid return ofSpartina(≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated withSpartinaalso quickly returned to its preinvasion state and was not distinguishable from that in uninvadedSpartinareference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat. [ABSTRACT FROM AUTHOR]

Pulsed resources, such as natural and anthropogenic inputs of nutrients into natural communities, can have important consequences for primary productivity, as well as for consumers and their predators. Little, however, is known of how a resource pulse influences community assemblages for periods longer than one growing season. This study, repeated twice and in two different habitats on a mid-Atlantic Spartina alterniflora salt marsh, showed that a one-time nitrogen (N) subsidy can have not only significant within-year effects on plant primary production and herbivore and natural enemy abundance, but can also have long-term effects on plants and arthropod food web structure. Spartina plants exhibited significantly greater biomass for 2-3 yr and elevated percentage of N for up to two years following the nutrient pulse, an effect that had direct positive effects on herbivores that were sensitive to variation in plant N content. Populations of Prokelisia planthoppers (Hemiptera: Delphacidae) were elevated in fertilized plots for up to three years following the nutrient addition. However, Trigonolylus uhieri, an herbivorous mind (Hemiptera: Miridae), was more abundant on previously fertilized plants only for a brief time, either within the same season as the nutrient addition, or for only one year after the pulse. The carryover effect of the nutrient pulse on plants and herbivores also propagated to the third trophic level. Both non-lycosid spiders (mostly linyphiids) and a specialist egg predator of Spartina planthoppers (Tytthus vagus) were more abundant in previously fertilized plots for up to two years following the nutrient pulse. In contrast, wolf spider (Lycosidae) densities were elevated in fertilized plots only within the same season as the initial fertilization pulse. Food web structure, as indexed by herbivore:predator ratio, was altered in plots that received a one-time N subsidy, with the arthropod food web in fertilized Spartina taking three years to resemble that of unperturbed Spartina. The response of particular herbivores and predators to the nutrient pulse was in part habitat dependent (contiguous Spartina meadows vs. isolated islets), suggesting that habitat heterogeneity combined with the differential dispersal ability of arthropods can influence the long-term response of a food web to a nutrient pulse. [ABSTRACT FROM AUTHOR]

Abstract: Cultivation of biofuel crops could change agricultural landscapes, affecting natural enemies at multiple scales. We sampled five natural enemy families with sticky cards in three model biofuel habitats (corn, switchgrass and prairie; n =60) across southern Michigan and Wisconsin, comparing captures between habitats and relating them to the area of forest, annual crop and herbaceous perennial habitat in the landscape within 2km of sites. In a first analysis, we compared Coccinellidae assemblages between habitats and examined the impact of habitat type and landscape composition on species richness and abundance. Results showed that, at the habitat scale, perennial grasslands supported a greater abundance of uncommon, native coccinellids and hosted distinct species assemblages compared to corn. At a broader scale, abundances of exotic and uncommon native ladybeetles responded differently to landscape composition, decreasing with the area of herbaceous perennials and annual crops, respectively. In a second analysis, we related family-level abundances of Anthocoridae, Syrphidae, Dolichopodidae and Chrysopidae to habitat type and landscape composition. Dolichopodids were more abundant in grasslands, while anthocorid and syrphid abundance increased over fivefold with the area of herbaceous, perennial habitat in the landscape surrounding corn, but not grassland, sites. These findings suggest that perennial grasslands used for bioenergy production could conserve natural enemies which are less abundant in corn, the dominant biofuel in existing landscapes. Moreover, cultivating annual cropland with herbaceous, perennial habitats could affect the abundance of natural enemies in existing crops and alter the suitability of entire landscapes for these beneficial taxa. [Copyright &y& Elsevier]