Diverse landscapes have a higher abundance and species richness of spring wild bees by providing complementary floral resources over bees’ foraging periods

Context

Anthropogenic landscape simplification and natural habitat loss can negatively affect wild bees. Alternatively, anthropogenic land-use change may diversify landscapes, creating complementary habitats that maintain overall resource continuity and diversity.

Objectives

We examined the effects of landscape composition, including land-cover diversity and percent semi-natural habitat, on wild bee abundance and species richness within apples, a pollinator-dependent crop. We also explored whether different habitats within diverse landscapes can provide complementary floral resources for bees across space and time.

Methods

We sampled bees during apple bloom over 2 years within 35 orchards varying in surrounding landscape diversity and percent woodland (the dominant semi-natural habitat) at 1 km radii. To assess habitat complementarity in resource diversity and temporal continuity, we sampled flowers and bees within four unique habitats, including orchards, woodlands, semi-natural grasslands, and annual croplands, over three periods from April–June.

Results

Surrounding landscape diversity positively affected both wild bee abundance and richness within orchards during bloom. Habitats in diverse landscapes had different flower communities with varying phenologies; flowers were most abundant within orchards and woodlands in mid-spring, but then declined over time, while flowers within grasslands marginally increased throughout spring. Furthermore, bee communities were significantly different between the closed-canopy habitats, orchards and woodlands, and the open habitats, grasslands and annual croplands.

Conclusions

Our results suggest that diverse landscapes, such as ones with both open (grassland) and closed (woodland) semi-natural habitats, support spring wild bees by providing flowers throughout the entire foraging period and diverse niches to meet different species’ requirements.

     

Agriculturally intensified landscapes are associated with reduced body condition of lady beetles

Landscape Ecology - Agricultural intensification is contributing to a global species decline. Underlying mechanisms include toxic effects of pesticides on non-target organisms and reductions in...     

Tree plantations on a grassland region: effects on methane uptake by soils

We assessed the rates of methane uptake (CH₄) by soils of different tree plantations and a control to provide information regarding potential greenhouse gas sequestration by tree plantations of pines, mixed deciduous species and eucalyptus in a natural grassland around 37S, 59W (Argentinean Pampa). A naturalized pasture was used as control. All sites had been agricultural and livestock lands. Each site was sampled three times from December 2012 to May 2013, using five static chambers randomly distributed across an area of ~100 m² in each site. In the control, methane fluxes were very weak; both negative (uptake) and positive (emission) values were found. Below tree plantations, fluxes were always negative, with statistically significant intersite differences. The highest uptake rates were observed in the mixed deciduous plantation (~10 ng m^?2 s^?1), followed by pines and eucalyptus plantations. Intrasite differences associated with spatial variation were also found. A significant inverse correlation between CH₄ uptake and soil water content was found in the pine and deciduous species plantations (R² > 0.94, p < 0.1).     

Power Requirements of Hemp Cutting and Conditioning

Laboratory experiments were conducted on cutting hemp (Cannabis sativa L.) using a sickle knife section and a countershear to determine the mechanical properties of the stems. The results showed that the cutting force and energy were significantly greater at a higher moisture content and specific mass of hemp stem. The average values of the maximum force and the total cutting energy required for cutting a hemp stem were 243 N and 2·1 J, respectively, which were much higher than those reported in the literature for cutting forage crops and maize stalk. Based on the laboratory results, the cutting power requirement in a field situation was estimated using the specific mass of hemp stem and machine feed rate. Power requirement associated with feed rate was investigated in a field experiment of cutting hemp using a reciprocating cutterbar mower operated at three different feed rates. Field conditioning experiments were also conducted to investigate the power requirement for conditioning hemp and a forage crop (alfalfa). The results showed that conditioning hemp required 10–60% more specific energy than conditioning alfalfa.     

Hypothalamic reward mechanism: two first-stage fiber populations with a cholinergic component

Refractory periods were estimated for fibers of the hypothalamic substrate of brain stimulation reward. Two nonoverlapping populations were evident: a homogeneous fast population and a more heterogeneous slow population. Cholinergic blockade eliminated the contribution of the fast but not the slow fibers, while dopaminergic blockade reduced responding without significantly influencing either directly activated fiber population. These data indicate that the hypothalamic reward substrate is more complex than has been widely appreciated; it contains two or more parallel subsystems, and one of these subsystems has a cholinergic link.     

‘Scalescape’: an R package for estimating distance-weighted landscape effects on an environmental response

Landscape Ecology - Landscape studies often focus on determining how the landscape around a discrete set of field sites affects an abiotic or biotic response measured at those sites. To run this...     

Within-Year Effects of Prescribed Fire on Bumble Bees (Hymenoptera: Apidae) and Floral Resources

Despite the importance of bumble bees (genus Bombus Latreille) for their services to natural and agricultural environments, we know little about the relationship between grassland management practices and bumble bee conservation. Prescribed fire is a common grassland maintenance tool, including in areas where endangered and threatened bumble bees are present. Thus, knowledge of the effects of prescribed fire on bumble bees is essential for designing management schemes that protect and bolster their populations. Using nonlethal surveys to record bumble bee species richness, abundance, and community composition, we evaluated the effects of spring controlled burns on summer bumble bee gynes and workers across five sites in southern Wisconsin. In addition, we explored the effects of fire on floral resources by measuring floral genus richness, abundance, ground cover, and proportion of transects containing blooming flowers in adjacent burned and unburned parcels. Prescribed fire had no measurable effects on bumble bee gyne or worker community composition, species richness, or abundance. However, consistent with previous studies prescribed fire increased floral genus richness and ground cover. The disconnect between bumble bee and floral responses to fire highlights some opportunities for improving our understanding of fire’s effects on bumble bee diapause, nest site choice, and foraging.     

Modeling a cross-ecosystem subsidy: forest songbird response to emergent aquatic insects

Context

Resource movements across ecosystem boundaries are important determinants of the diversity and abundance of organisms in the donor and recipient ecosystem. However the effects of cross-ecosystem movements of materials at broader spatial extents than a typical field study are not well understood.

Objectives

We tested the hypotheses that (1) variation in abundance of 57 forest songbird species within four foraging guilds is explained by modeled emergent aquatic insect biomass inputs from adjacent lakes and streams and (2) the degree of association varies across foraging guilds and species within guilds. We also sought to determine the importance of emergent aquatic insects while accounting for variation in local forest cover and edge.

Methods

We spatially modeled the degree to which distribution and abundance of songbirds in different foraging guilds was explained by modeled emergent aquatic insect biomass. We used multilevel models to simultaneously estimate the responses of species in four different insectivorous guilds. Bird abundance was summarized from point counts conducted over 24 years at 317 points.

Results

Aerial insectivores were more abundant in areas with high estimated emergent insect biomass inputs to land (regression coefficient 0.30, P?<?0.05) but the overall abundance of gleaners, bark-probers, and ground-foragers was not explained by estimated emergent insect abundance. The coursing aerial insectivores had the strongest association with emergent insects followed by willow flycatcher, olive-sided flycatcher, and alder flycatcher.

Conclusions

Modeling cross-ecosystem movements of materials at broad spatial extents can effectively characterize the importance of this ecological process for aerial insectivorous songbirds.