Impact of native predators and parasites on Spodoptera exigua, an introduced pest of alfalfa hay in northern California

A long-term study of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) revealed that a complex of native predators and parasites exploit this introduced pest in alfalfa-hay fields in northern California. In field trials, predators typically fed on >50% of sentinel egg masses during a given sample interval; mean predation rate ranged from 40 to 100% and percentage predation per individual egg mass was density-independent (spatial context) for 16 of 17 sample intervals. The egg-predator guild consisted primarily of adults and nymphs of Lygus hesperus Knight & L. elisus Van Duzee (Miridae), Nabis americoferus Carayon (Nabidae), and Orius tristicolor (White) (Anthocoridae); and adults of Collops vittatus (Say) (Melyridae) and Hippodamia convergens Guerin-Meneville (Coccinellidae). In laboratory feeding trials, these species readily fed on eggs, as well as neonate larvae of S. exigua. The parasite guild associated with small- to medium-sized larvae consisted of Hyposoter exiguae (Viereck) and Pristomerus spinator (F.) (Ichneumonidae), both larval endoparasites; and Chelonus insularis Cresson (Braconidae), an egg-larval endoparasite. Total parasitization by these species in field samples ranged from 5 to 75%, and was density-independent (spatial context) for each of four sample dates. A few larvae were infected with a nuclear polyhedrosis virus but no epizootics were observed. These results are consistent with the hypothesis that native natural enemies, especially generalist predators, can maintain populations of S. exigua at levels well below the treatment threshold for this exotic pest of alfalfa grown for hay.     

Seasonality of a Diverse Beetle Assemblage Inhabiting Lowland Tropical Rain Forest in Australia

One of the least understood aspects of insect diversity in tropical rain forests is the temporal structuring, or seasonality, of communities. We collected 29,986 beetles of 1473 species over a 4-yr period (45 monthly samples), with the aim to document the temporal dynamics of a trophically diverse beetle assemblage from lowland tropical rain forest at Cape Tribulation, Australia. Malaise and flight interception traps were used to sample adult beetles at five locations at both ground and canopy levels. Beetles were caught throughout the year, but individual species were patchy in their temporal distribution, with the 124 more abundant species on average being present only 56 percent of the time. Climatic variables (precipitation, temperature, and solar radiation) were poorly correlated with adult beetle abundance, possibly because: (1) seasonality of total beetle abundance was slight; (2) the peak activity period (September–November) did not correspond to any climatic maxima or minima; or (3) responses were nonlinear owing to the existence of thresholds or developmental time-lags. Our results do not concur with the majority of tropical insect seasonality studies suggesting a wet season peak of insect activity, perhaps because there is no uniform pattern of insect seasonally for the humid tropics. Herbivores showed low seasonality and individual species' peaks were less temporally aggregated compared to nonherbivores. Canopy-caught and larger beetles (> 5 mm) showed greater seasonality and peaked later in the year compared to smaller or ground-caught beetles. Thus seasonality of adult beetles varied according to the traits of feeding ecology, body size, and habitat strata.     

Feeding guilds and food resource partitioning in a lake fish assemblage: an ontogenetic approach

Ontogenetic diet patterns and trophic guild structure of a 15 species temperate lake fish assemblage were analysed over wide size intervals (up to seven orders of magnitude in body mass), representing practically the whole life span in most species. A two-step objective clustering technique supplemented with other multivariate statistical tools proved that size-related diet changes clearly played an important role in structuring trophic organization of fishes inhabiting Lake Balaton. As many as 13 out of the 15 fish species showed marked size-related dietary changes with two to four ontogenetic feeding stages. At the assemblage level, 11 trophic guilds were separated. Guild membership was size-dependent in 11 fish species that participated in two to four trophic guilds during their life span. The most complex trophic ontogeny was observed in roach Rutilus rutilus and asp Aspius aspius with four guild memberships. This study showed that trophic status of fishes may be very size-sensitive and thus a universal classification of fish species to general trophic guilds, such as 'planktivore', 'benthivore', 'piscivore' or 'herbivore', should be applied very carefully even in environmental monitoring and fisheries management applications, unless it is supported by relevant results of life span diet analyses.     

The global distribution of frugivory in birds

Aim To examine patterns of avian frugivory across clades, geography and environments. Location Global, including all six major biogeographical realms (Afrotropics, Australasia, Indo‐Malaya, Nearctic, Neotropics and Palaearctic). Methods First, we examine the taxonomic distribution of avian frugivory within orders and families. Second we evaluate, with traditional and spatial regression approaches, the geographical patterns of frugivore species richness and proportion. Third, we test the potential of contemporary climate (water–energy, productivity, seasonality), habitat heterogeneity (topography, habitat diversity) and biogeographical history (captured by realm membership) to explain geographical patterns of avian frugivory. Results Most frugivorous birds (50%) are found within the perching birds (Passeriformes), but the woodpeckers and allies (Piciformes), parrots (Psittaciformes) and pigeons (Columbiformes) also contain a significant number of frugivorous species (9–15%). Frugivore richness is highest in the Neotropics, but peaks in overall bird diversity in the Himalayan foothills, the East African mountains and in some areas of Brazil and Bolivia are not reflected by frugivores. Current climate explains more variance in species richness and proportion of frugivores than of non‐frugivores whereas it is the opposite for habitat heterogeneity. Actual evapotranspiration (AET) emerges as the best single climatic predictor variable of avian frugivory. Significant differences in frugivore richness and proportion between select biogeographical regions remain after differences in environment (i.e. AET) are accounted for. Main conclusions We present evidence that both environmental and historical constraints influence global patterns of avian frugivory. Whereas water–energy dynamics possibly constrain frugivore distribution via indirect effects on food plants, regional differences in avian frugivory most likely reflect historical contingencies related to the evolutionary history of fleshy fruited plant taxa, niche conservatism and past climate change. Overall our results support an important role of co‐diversification and environmental constraints on regional assembly over macroevolutionary time‐scales.     

An inventory of the foliar,soil, and dung arthropod communities in pastures of the southeastern United States

Grassland systems constitute a significant portion of the land area in the United States and as a result harbors significant arthropod biodiversity. During this time of biodiversity loss around the world, bioinventories of ecologically important habitats serve as important indicators for the effectiveness of conservation efforts. We conducted a bioinventory of the foliar, soil, and dung arthropod communities in 10 cattle pastures located in the southeastern United States during the 2018 grazing season. In sum, 126,251 arthropod specimens were collected. From the foliar community, 13 arthropod orders were observed, with the greatest species richness found in Hymenoptera, Diptera, and Hemiptera. The soil‐dwelling arthropod community contained 18 orders. The three orders comprising the highest species richness were Coleoptera, Diptera, and Hymenoptera. Lastly, 12 arthropod orders were collected from cattle dung, with the greatest species richness found in Coleoptera, Diptera, and Hymenoptera. Herbivores were the most abundant functional guild found in the foliar community, and predators were most abundant in the soil and dung communities. Arthropod pests constituted a small portion of the pasture arthropod communities, with 1.01%, 0.34%, and 0.46% pests found in the foliar, soil, and dung communities, respectively. While bioinventories demand considerable time, energy, and resources to accomplish, the information from these inventories has many uses for conservation efforts, land management recommendations, and the direction of climate change science.     

Spiders as potential indicators of elephant‐induced habitat changes in endemic sand forest,Maputaland, South Africa

Elephant impacts on spider assemblages, and the potential use of spiders as indicators of habitat changes was assessed in central Maputaland, South Africa. Three habitats, namely undisturbed sand forest, elephant disturbed sand forest and mixed woodland, were sampled. To ensure a thorough representation of all spider guilds, spiders were collected by tree beating, sweep netting, active searching, leaf litter sifting and pitfall traps. In total, 2808 individual spiders, representing 36 families, 144 determined genera and 251 species were collected. Spider abundance was highest in the undisturbed sand forest (n = 1129, S = 179), followed by elephant disturbed sand forest (n = 1006, S = 165) and mixed woodland (n = 673, S = 171). Assemblages of the two sand forests were more similar than to the mixed woodland assemblage. Active hunting species were indicators of the more open vegetation of elephant disturbed sand forest (six active hunters, no web‐builders) and mixed woodland (ten active hunters, one web‐builder), whereas web‐builders are indicators of the dense, complex vegetation structure of undisturbed sand forest (six web‐builders, three active hunters). Elephant‐induced changes to the vegetation structure in this high diversity, high endemism region result in changes in the composition of spider assemblages, and may need to be mitigated by management intervention.     

Effect of the Environmental Factors on the Caloric Content of Benthic and Phytophilous Invertebrates in Neotropical Reservoirs in the Paraná State,Brazil

The complexity of the relations between the organisms and the environment are reflected through the energy content. So we tested the hypothesis on body energy content variation in invertebrates and its relation with some environmental factors (season, habitat type, trophic status and trophic guild). We expected higher energy values for phytophilous fauna, rainy season, in reservoirs with higher trophic levels and for herbivorous invertebrates. The results showed the influence of seasonality and trophic status of the reservoir on the energy content of invertebrates, which was higher in the rainy season and in the mesotrophic reservoirs, due to the input of allochthonous material during this season, confirming our initial prediction. A higher caloric content was recorded for carnivorous and detritivorous invertebrates. The differences between the trophic guilds were primarily related to the opportunistic feeding behavior, which may be considered as one of the main factors controlling the energy flow of benthic and phytophilous invertebrates. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Beetle assemblages in ponds: effects of habitat and site age

• 1 Water beetle assemblages were sampled in each of 18 freshwater ponds, including 11 recently constructed sites designed to provide mitigation for wetlands destruction elsewhere, and seven older reference sites. There were three objectives: (a) to relate taxon richness and biomass of the beetles to the same properties of the wider aquatic invertebrate community, (b) to evaluate changes in beetle assemblage structure over time, and (c) to determine habitat effects on taxonomic composition, mean body size and trophic guild structure of the beetle assemblage.
• 2 Forty‐seven beetle genera were identified, representing 77 species. The beetles represented an average of 21.5% of total generic richness, but only 3.7% of total wet biomass of the wider invertebrate community.
• 3 Of all variables evaluated using canonical correspondence analysis (CCA), site age had the greatest influence on the beetle assemblage. Predatory dytiscids were early colonists at younger sites, while herbivorous curculionids and chrysomelids associated with particular types of vegetation typically occurred in older ponds. Mitigation ponds and reference ponds supported similar numbers of species. Reference sites, however, harboured substantially more unique species found at only a single site within the study area.
• 4 The presence of fish was also strongly related to beetle assemblage structure. Ponds with few or no fish contained about 3‐fold higher biomass and 3‐fold greater mean wet weight per individual compared to ponds with substantial fish assemblages.
• 5 Beetle assemblage composition varied among sites and sampling years, but beetle biomass, richness and species composition may be useful tools in evaluating the success of wetland mitigation efforts.

     

El Niño events,the lean versus fat scenario,and long‐term guild dynamics of vertebrate predators in a South American semiarid ecosystem

Abstract Predator assemblages are complex systems in which asynchrony in the dynamics of resources and consumers, and the idiosyncratic perception of environmental conditions by the predators may obscure the detection of expected patterns. We disentangle the specific effects of these variables on the guild structure of a vertebrate predatory assemblage in a semiarid ecosystem of western South America. Over 16 years, this system faced dramatic fluctuations in prey availability associated with four El Niño events. After controlling for other sources of variation, we tested if increased resource availability is associated with higher niche overlaps, as expected from the lean/fat scenario. We determined the existence of two trophic guilds of predators (specialized mammal‐eaters and omnivorous species with emphasis on arthropods) and found that they responded to increased productivity both at the guild and whole assemblage levels. However, the population response of arthropod prey (almost simultaneous) and of different small mammal prey (delayed by 1 or 2 years) to productivity imposed a degree of asynchrony in prey availability and in the response of predators. This resulted in the between‐guilds exchange of predator species depending on mammal prey scarcity or abundance. As a consequence, the observed pattern was an apparent lack of response at the assemblage level. Despite differences in the perception of prey levels by predators, we conclude that each one of them responded accordingly to theoretical predictions following a simple rule: if prey resources are not limiting, predators behave opportunistically converging over the most abundant resources, thus increasing niche overlap; if prey shortages occur, predators specialize on those prey resources that they gather most efficiently, thus lowering niche overlap; if resources become even scarcer, all predators converge again upon the few prey resources still available, thus increasing overlap – out of necessity.     

Species of street tree is important for southern hemisphere bird trophic guilds

Abstract Urban environments are highly modified with unique assemblages of bird species. Much of the research on urban bird assemblages comes from the northern hemisphere. Southern hemisphere bird assemblages differ from northern hemisphere assemblages in that they contain a large proportion of nectarivores. In this study we focus on bird use of street trees in Australia. We investigate the relative influence of tree species (plane tree, Platanus x acerifolia; red gums, Eucalyptus camaldulensis; jacaranda, Jacaranda mimosifolia; bottlebrush, Callistemon citrinus), season and the environment surrounding street trees, on the abundance and species richness of birds in Adelaide, South Australia. Our study considers birds in terms of granivore, nectarivore and insectivore trophic guilds. Nectarivores accounted for the greatest proportion of observations, in terms of abundance, in each of the tree species investigated. Species of street tree was a significant influence on bird use of the trees for all birds and each dietary guild. Red gums were used more than the other tree species by nectarivores, while plane trees were used more than the other trees by insectivores. Use of the tree species by granivores varied with the season. The measures of the environment surrounding street trees were largely unimportant with the exception of traffic for nectarivores in some cases. Urban avifauna use street trees and the species of tree will strongly influence its use by birds. However, the pattern of use of street tree species varied at different times of year and differed between different trophic guilds of birds. The dominance of nectarivores in the southern avifauna will likely produce different patterns of urban environment use to northern hemisphere avifaunas.