Spatial and temporal variation in species composition of dung beetle assemblages in southern Ireland

Abstract. 1. This study attempts to identify the main community characteristics that contribute to variability in dung beetle assemblage composition and structure across a range of spatial and temporal scales.
2. Dung beetle assemblages ( Aphodius , Sphaeridium, and Geotrupes species) were monitored by dung-baited pitfall trapping at 10-day intervals during the seasonally active period at eleven sites in southern Ireland. Three of the sites were monitored over at least 2 years between 1991 and 1996.
3. Although the species composition of the above taxonomic groups was comparable among sites and years, relative abundances of component species varied considerably. Detrended correspondence analysis ordinations indicated a similar level of variability in dung beetle assemblage structure among years, and among sites ≈1–180 km apart.
4. Processes that may contribute to spatio-temporal variability in dung beetle assemblages are discussed, and strategies for future research are suggested.     

Spatial and temporal variation of photosynthetic parameters in natural phytoplankton assemblages in the Beaufort Sea, Canadian Arctic

During summer 2008, as part of the Circumpolar Flaw Lead system study, we measured phytoplankton photosynthetic parameters to understand regional patterns in primary productivity, including the degree and timescale of photoacclimation and how variability in environmental conditions influences this response. Photosynthesis–irradiance measurements were taken at 15 sites primarily from the depth of the subsurface chlorophyll a (Chl a) maximum (SCM) within the Beaufort Sea flaw lead polynya. The physiological response of phytoplankton to a range of light levels was used to assess maximum rates of carbon (C) fixation (P _m^*), photosynthetic efficiency (α ^*), photoacclimation (E _k), and photoinhibition (β ^*). SCM samples taken along a transect from under ice into open water exhibited a >3-fold increase in α ^* and P _m^*, showing these parameters can vary substantially over relatively small spatial scales, primarily in response to changes in the ambient light field. Algae were able to maintain relatively high rates of C fixation despite low light at the SCM, particularly in the large (>5 μm) size fraction at open water sites. This may substantially impact biogenic C drawdown if species composition shifts in response to future climate change. Our results suggest that phytoplankton in this region are well acclimated to existing environmental conditions, including sea ice cover, low light, and nutrient pulses. Furthermore, this photoacclimatory response can be rapid and keep pace with a developing SCM, as phytoplankton maintain photosynthetic rates and efficiencies in a narrow “shade-acclimated” range.     

Spatial mechanisms for coexistence of species sharing a common natural enemy

We examine the conditions under which spatial structure can mediate coexistence of apparent competitors. We use a spatially explicit, host-parasitoid metapopulation model incorporating local dynamics of Nicholson-Bailey type and global dispersal. Depending on the model parameters, the resulting system displays a plethora of asynchronous dynamical behaviors for which permanent or transient coexistence is observed. We identify a number of spatially mediated tradeoffs which apparent competitors can utilize and demonstrate that the dynamics of spatial coexistence can typically be understood from consideration of two and three patch systems. The phase relationships of species abundances are different for our model than for some other mechanisms of spatial coexistence. We discuss the implications of our findings relative to issues of community organization and biological conservation.     

Parasitic wasp assemblages associated with native and weedy plant species in an agricultural landscape

Abstract  The establishment and maintenance of suitable habitat on-farm or in the surrounding landscape can enhance the survival of beneficial parasitic Hymenoptera, thus improving the control of pest species. Both endemic and weedy non-crop plant species across a highly modified agricultural landscape supported species-rich and abundant parasitic wasp assemblages with diverse biology and host associations. It was also shown that isolated, recently planted, single-species stands of plants can rapidly accumulate diverse assemblages of parasitoids. Chalcidoidea was the most species-rich and abundant group, egg and larval parasitoids were the most speciose and abundant guilds, and parasitoids of herbivorous insects feeding on and inside plant tissue were the most species-rich and abundant functional groups. The hymenopteran assemblages associated with the majority of plant species were dominated by three parasitoid species: a Trichogrammatidae, a Scelionidae ( Telenomus sp.) and a Eulophidae ( Ceranisus sp.), all genera that contain many important biocontrol agents of pest Lepidoptera, Hemiptera and Thysanoptera. Results show that both native and weedy plant species may potentially provide an important reservoir of mobile parasitic wasps of benefit to crop protection.     

Spatial and temporal variation of fish assemblages in a subtropical small stream of the Huangshan Mountain

Spatial and temporal variation of fish assemblages were investigated seasonally from May 2007 to February 2008 across 11 study sites in a subtropical small stream, the Puxi Stream, of the Huangshan Mountain. Along the longitudinal gradient from headwater to downstream, fish species richness and abundance increased gradually, but then decreased significantly at the lower reaches. The highest species richness and abundance were observed in August and the lowest in February. Based on analysis of similarities (...     

Spatial phylogenetics of the native woody plant species in Hainan,China

To better identify biodiversity hotspots for conservation on Hainan Island, a tropical island in southern China, we assessed spatial variation in phylogenetic diversity and species richness using 18,976 georeferenced specimen records and a newly reconstructed molecular phylogeny of 957 native woody plants. Within this framework, we delineated bioregions based on vegetation composition and mapped areas of neoendemism and paleoendemism to identify areas of priority for conservation. Our results reveal that the southwest of Hainan is the most important hot spot for endemism and plant diversity followed by the southeast area. The distribution of endemic species showed a scattered, rather than clustered, pattern on the island. Based on phylogenetic range‐weighted turnover metrics, we delineated three major vegetational zones in Hainan. These largely correspond to natural secondary growth and managed forests (e.g., rubber and timber forests) in central Hainan, old‐growth forests and natural secondary growth forest at the margins of Hainan, and nature reserves on the island (e.g., Jianfeng and Diaoluo National Nature Reserves). Our study helps to elucidate potential botanical conservation priorities for Hainan within an evolutionary, phylogenetic framework.     

Direct and indirect effects of plant genetic variation on enemy impact

Abstract.

• 1 The Tritrophic and Enemy Impact concepts predict that natural enemy impact varies: (a) among plant genotypes and (b) may depend on the abundance of heterospecific herbivores, respectively. I tested these predictions using three herbivore species on potted, cloned genotypes of Salik sericea Marshall in a common garden experiment.
• 2 Densities of the leaf miner (Phyllonorycter salicifoliella (Chambers)) and two leaf galling sawflies (Phyllocolpa nigrita (Marlatt) and Phyllocolpa eleanorae Smith and Fritz) varied significantly among willow clones, indicating genetic variation in resistance.
• 3 Survival and natural enemy impact caused by egg and larval parasitoids and/or unknown predators differed significantly among willow clones for each of the three herbivore species, indicating genetic variation in survival and enemy impact.
• 4 Survival of Phyllonorycter was negatively density-dependent among clones.
• 5 Survival of Phyllonorycter and Phyllocolpa eleanorae were positively correlated with densities of heterospecific herbivores among clones and parasitism of these species were negatively correlated with densities of the same heterospecific herbivores among clones.
• 6 At least for Phyllonorycter this positive correlation may suggest either facilitation of survival between herbivore species, which do not share natural enemies, or an apparent interaction caused by host plant genetic variation.
• 7 Among clones, egg parasitism of Phyllocolpa eleanorae was weakly positively correlated with density of Phyllocolpa nigrita. Since these species share the same Trichogramma egg parasitoid, this interaction could support the hypothesis of apparent competition.

     

Using variation partitioning techniques to quantify the effects of invasive alien species on native urban bird assemblages

Quantifying the impacts that invasive alien species (IAS) cause on affected systems is not an easy task. Here, we explore the application of variation partitioning techniques to measure and control for the effects of possible confounding factors when studying the impact that feral pigeons, European starlings, and house sparrows cause on native urban bird communities in Mexico. We argue that these IAS are provoking a severe impact on whole assemblages of native passerines only if (a) their marginal effect is statistically significant, (b) it remains so after partialling out other explanatory variables, and (c) is larger than (or similar to) the conditional effect of these covariates. We censused passerine bird assemblages and measured habitat variables in a number of greenspaces in three replicate study areas. Then, by means of partial redundancy analyses, we decomposed the total variability in bird data as a function of IAS, physical variables and vegetation data. In one of the study areas the marginal effect of IAS on native assemblages was significant, but the conditional effect was not. We conclude that this IAS effect was confounded with other explanatory variables. In the other study areas, no (marginal or partial) significant effect was found. Without invoking interspecific competition, our results support the opportunistic hypothesis, according to which IAS can exploit ecological conditions in modern cities that native species cannot even tolerate. Finally, apart from the Precautionary Principle, we found no scientific justification to control the abundance of the three IAS in our study areas.     

The effect of past natural enemy activity on host‐plant preference of two aphid species

The selection of a host of high nutritional quality is of great importance to the development of offspring of larvipositing aphids, as is the avoidance of natural enemies. Little is known, however, about their ability to select host plants based on these factors. This article tests the preference of aphids Sitobion avenae (Fabricius) and Rhopalosiphum padi (L.) (both Hemiptera: Aphididae) for different winter wheat cultivars, Triticum aestivum (L.) (Poaceae), and their ability to detect and avoid predators in sacrifice of their most preferred host. In both species a preference was observed for nutritionally superior hosts. The preference of both species then exhibited a change towards a nutritionally inferior host after infestations of the harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), that had been consuming conspecific aphids. This investigation opens the door to the interesting prospect of the ability of aphids to make complex decisions regarding a compromise between high‐quality nutrition and avoidance of predation.     

Spatial variation in the ongoing and widespread decline of a keystone plant species

Extensive dieback in dominant plant species in response to climate change is increasingly common. Climatic conditions and related variables, such as evapotranspiration, vary in response to topographical complexity. This complexity plays an important role in the provision of climate refugia. In 2008/2009, an island‐wide dieback event of the keystone cushion plant Azorella macquariensis Orchard (Apiaceae) occurred on sub‐Antarctic Macquarie Island. This signalled the start of a potential regime shift, suggested to be driven by increasing vapour pressure deficit. Eight years later, we quantified cover and dieback across the range of putative microclimates to which the species is exposed, with the aim of explaining dieback patterns. We test for the influence of evapotranspiration using a suite of topographic proxies and other variables as proposed drivers of change. We found higher cover and lower dieback towards the south of the island. The high spatial variation in A. macquariensis populations was best explained by latitude, likely a proxy for macroscale climate gradients and geology. Dieback was best explained by A. macquariensis cover and latitude, increasing with cover and towards the north of the island. The effect sizes of terrain variables that influence evapotranspiration rates were small. Island‐wide dieback remains conspicuous. Comparison between a subset of sites and historical data revealed a reduction of cover in the north and central regions of the island, and a shift south in the most active areas of dieback. Dieback remained comparatively low in the south. The presence of seedlings was independent of dieback. This study provides an empirical baseline for spatial variation in the cover and condition of A. macquariensis, both key variables for monitoring condition and ‘cover‐debt’ in this critically endangered endemic plant species. These findings have broader implications for understanding the responses of fellfield ecosystems and other Azorella species across the sub‐Antarctic under future climates.     

Spatial and temporal variations in nematode assemblages in tropical seagrass sediments

The changes in the community dynamics of infaunal nematodes associated with tropical Australian intertidal seagrasses at 4 estuarine sites were investigated through 3 seasons (autumn, winter and spring). Nematode densities were highest in winter in all but one of the sites, ranging from 1971 to 3084 inds./10 cm², with one site showing a highest density of 3411 inds./10 cm² in spring. Multiple regression revealed significant correlations between nematode density peaks and seasonal changes in temperature, salinity and surface seagrass cover. Non-metric Multi-Dimensional Scaling revealed that the communities were characterised by relatively low within-site spatial variability but relatively high temporal variability through the three seasons. This temporal variability was largely due to significant increases in abundance of epistrate-feeding species in winter and spring. An investigation of the dominant epistrate-feeding nematodes revealed that predominantly infaunal species were responsible for overall winter and spring density increases. This study provides further evidence of the role played by temperature in regulating tropical, intertidal meiobenthic communities but also indirectly provides evidence of micro-scale seagrass canopy effects (micro-algal supply and availability) that may further enhance the impacts of these larger-scale seasonal environmental changes on the infaunal nematode community.     

Spatial and temporal variation in fish assemblages of drying stream pools: The role of abiotic and biotic factors

Droughts and summer drying create unusual temporary aquatic habitats in the form of isolated pools in many small streams around the world. To examine spatial and temporal variation in fish community structure of drying stream pools, their relation to abiotic environmental variables, and associations among species, fish were sampled during summer 1995 and 1996 from pools of four streams in the Ozark mountains, Arkansas, USA. Redundancy analysis of physical-chemical variables showed significant differences among stream sites, but no significant difference between years or stream site by year interaction. Stream sites separated consistently along axes one (habitat heterogeneity) and two (temperature/canopy cover) in both years. Redundancy analysis of fish species-size class densities showed a significant stream site by year interaction. Groupings of stream sites based on fish assemblages were not well explained by physical-chemical variables measured at the pool scale, but were related to location within the drainage basin, and these groupings differed between years. There were 27 (15.8%) and 10 (5.8%) significant associations found among fish species-size classes in 1995 and 1996, respectively, and all but two significant associations in 1995 were positive. Pool depth, habitat heterogeneity, pool size and dissolved oxygen/canopy cover were important local abiotic factors depending on response variables examined. In both years, large fish total density, large central stoneroller density (80 mm TL), and small sunfish (<80 mm TL) density were positively related to pool depth. Otherwise, there was no consistent relationship between physical-chemical variables and dependent variables (fish density and species richness) within a year or between years for a given dependent variable. These results support the hypothesis that local abiotic factors are important in structuring fish assemblages in harsh environments, but the importance of those factors varies temporally, and regional influences appear to override local abiotic conditions as factors structuring fish assemblages in drying stream pools. Predation by terrestrial vertebrates may also be an important factor structuring these fish assemblages that has been largely overlooked.     

Plant characteristics associated with natural enemy abundance at Michigan native plants

Habitat management is a type of conservation biological control that focuses on increasing natural enemy populations by providing them with plant resources such as pollen and nectar. Insects are known to respond to a variety of plant characteristics in their search for plant-provided resources. A better understanding of the specific characteristics used by natural enemy insects in selecting these resources could greatly improve efficiency in screening plants for habitat management. We examined 5 previously tested and widely recommended resource plants and 43 candidate plants to test whether the number and type of natural enemies and herbivores at each plant were predicted by plant characteristics including: period of peak bloom, floral area, maximum flower height, hue, chroma, and corolla size. Natural enemy abundance increased with week of peak bloom and greater floral area across all plants tested. Ordination of plant characteristics indicated that increasing floral area, period of peak bloom, maximum flower height, and decreasing corolla width grouped together into a single principal component. Both natural enemy and herbivore abundance increased significantly with the principal component for this set of characteristics, but the relationship with herbivore abundance was weaker. These results indicate that, for a given time of the season, selection of plants with the largest floral area has potential to increase natural enemy abundance in habitat management plantings and streamline plant selection for habitat management.     

Spatial and temporal variation of consanguinity in Italy

Genetic structure of Italian population is described as regards the level of inbreeding measured through the frequency of consanguineous marriages during a long period of time in different geographical areas. Analyses of spatial and temporal variation of the different types of marriages between close biological relatives allow us to point out the major factors responsible for the availability of cousins to marry within a specific area: population size, fertility, mortality and migration rates and, in general the demographic structure, changing over time and greatly affected by variation in the socio-economic structure. A deepened analysis, within each consanguinity degree, of the various pedigrees differing in the sex of ancestors, give information on the type of migration (patrilocal or matrilocal) occurred in various parts of Italy, as probable consequence of differential type of economy (for instance: pastoral or agricultural in Sardinia). Moreover, a cultural factor of varying intensity could be recognized in the greater observed frequency of marriages in which the nearest ancestors are females, interpreted as a tendency to maintain family ties by mothers of consanguineous mates.     

Spatial and temporal variability of antibiotic resistance in freshwater bacterial assemblages

Abstract Spatial and temporal variability in antibiotic resistance was examined in bacterial assemblages from streams and ponds on the US Department of Energy's Savannah River Site (SRS) in South Carolina. Sites sampled have been impacted to varying degrees by contamination with organic compounds, heavy metals, and radioactive materials because of production of nuclear materials on the site. Antibiotic resistance in the culturable portion of the bacterial assemblage was determined from coloby formation on media containing antibiotics. Eight antibiotics, chloramphenicol, cycloserine, kanamycin, neomycin, novobiocin, rifampicin, streptomycin, and tetracycline, were used at concentrations of 50 and 200 μg ml⁻¹. Statistically significant differences in frequency of antibiotic resistance were observed among sites and among dates at a single site. Bacterial densities (total and culturable), dissolved organic carbon (DOC) concentration, and human impact also varied among sites but bore no overall relationship to resistance frequency. SRS operations did not have a detectable impact on antibiotic resistance.     

Side effects of flonicamide and pymetrozine on five aphid natural enemy species

The effects of flonicamide and pymetrozine, on inert and natural substrates, on the rove beetle Aleochara bilineata (Gyll.), the parasitic wasp Aphidius rhopalosiphi (DeStefani-Perez), the ladybird Adalia bipunctata (L.), the carabid beetle Bembidion lampros (Herbst), and the hoverfly Episyrphus balteatus (DeGeer) were assessed in the laboratory. Deltamethrin and pirimicarb were also tested as toxic reference compounds. The results indicated high selectivity of flonicamide and pymetrozine for all the species tested. No significant effects on B. lampros and A. bilineata were recorded for sand or on E. balteatus for plants. Pymetrozine on inert substrates had no effects on A. bipunctata larvae, whereas flonicamid was slightly toxic on glass plates but harmless on plants. Both compounds were toxic to adult A. rhopalosiphi on glass plates and on plants in the laboratory, but no effects were observed on plants treated in the field. In comparison, the toxic reference products were always more toxic. Compared with classical insecticides tested on the same species using similar methods, flonicamide and pymetrozine seem to be promising insecticides for aphid control in terms of selectivity for aphid antagonists.     

An exotic species is the favorite prey of a native enemy

Although native enemies in an exotic species'' new range are considered to affect its ability to invade, few studies have evaluated predation pressures from native enemies on exotic species in their new range. The exotic prey naiveté hypothesis (EPNH) states that exotic species may be at a disadvantage because of its naïveté towards native enemies and, therefore, may suffer higher predation pressures from the enemy than native prey species. Corollaries of this hypothesis include the native enemy preferring exotic species over native species and the diet of the enemy being influenced by the abundance of the exotic species. We comprehensively tested this hypothesis using introduced North American bullfrogs (Lithobates catesbeianus, referred to as bullfrog), a native red-banded snake (Dinodon rufozonatum, the enemy) and four native anuran species in permanent still water bodies as a model system in Daishan, China. We investigated reciprocal recognition between snakes and anuran species (bullfrogs and three common native species) and the diet preference of the snakes for bullfrogs and the three species in laboratory experiments, and the diet preference and bullfrog density in the wild. Bullfrogs are naive to the snakes, but the native anurans are not. However, the snakes can identify bullfrogs as prey, and in fact, prefer bullfrogs over the native anurans in manipulative experiments with and without a control for body size and in the wild, indicating that bullfrogs are subjected to higher predation pressures from the snakes than the native species. The proportion of bullfrogs in the snakes'' diet is positively correlated with the abundance of bullfrogs in the wild. Our results provide strong evidence for the EPNH. The results highlight the biological resistance of native enemies to naïve exotic species.     

Spatial and temporal variation in a suite of life-history traits in two species of wolf spider

Abstract.  1. Life-history traits and density were assayed in seven populations of two sympatric species of wolf spider for three consecutive years. The goal of the study was to quantify population dynamics and its relation to spatial and temporal life-history variation.
2. Adult female body size and fecundity varied significantly, among field sites and among years, in both species. Female spiders of both species differed in mean relative reproductive effort among sites, but not among years. The size of offspring was invariable, with no significant differences due to site or year.
3. All populations of both species tended to either decrease or increase in density during a given year and this was tightly correlated with changes in prey consumption rates.
4. Since life-history patterns are determined primarily by selection, it is concluded that size at sexual maturity for females is phenotypically plastic and responds to changes in prey availability. Offspring size however is not plastic and it is likely that other selection forces have determined offspring size. Temporal fluctuations in population size are correlated over a large area relative to dispersal capabilities for these species and conservation efforts for invertebrates must take this into consideration.     

Floral neighborhood influences pollinator assemblages and effective pollination in a native plant

Pollinators represent an important intermediary by which different plant species can influence each other’s reproductive fitness. Floral neighbors can modify the quantity of pollinator visits to a focal species but may also influence the composition of visitor assemblages that plants receive leading to potential changes in the average effectiveness of floral visits. We explored how the heterospecific floral neighborhood (abundance of native and non-native heterospecific plants within 2 m × 2 m) affects pollinator visitation and composition of pollinator assemblages for a native plant, Phacelia parryi. The relative effectiveness of different insect visitors was also assessed to interpret the potential effects on plant fitness of shifts in pollinator assemblage composition. Although the common non-native Brassica nigra did not have a significant effect on overall pollinator visitation rate to P. parryi, the proportion of flower visits that were made by native pollinators increased with increasing abundance of heterospecific plant species in the floral neighborhood other than B. nigra. Furthermore, native pollinators deposited twice as many P. parryi pollen grains per visit as did the nonnative Apis mellifera, and visits by native bees also resulted in more seeds than visits by A. mellifera. These results indicate that the floral neighborhood can influence the composition of pollinator assemblages that visit a native plant and that changes in local flower communities have the potential to affect plant reproductive success through shifts in these assemblages towards less effective pollinators.