Niche partitioning based on nest site selection in the small carpenter bees Ceratina mikmaqi and C. calcarata

High temperature sensitivity of bumblebee castes and the colony-level costs of thermoregulation in Bombus impatiens

Physiological thermal limits often reflect species distribution, but the role that ambient temperature (Ta) plays in limiting species within their thermal environment remains unclear. Climate change-linked declines in bumblebees, an important pollinator group, leave questions regarding which aspect of their physiology is hindered under high Ta. As a eusocial species, bumblebees utilize their ability to thermoregulate as a superorganism to maintain nest temperature (Tn) within a narrow thermal window to buffer developing larvae from developmental defects. Thermoregulatory behaviours, such as thermogenesis to warm up and fanning to cool down the nest, are energetically expensive and it is uncertain how successful large colonies are at maintaining Tn within its optimal range. Using a common bumblebee species, Bombus impatiens, our study first established the critical thermal limits (CTmax) of workers, queens, drones and larvae to determine which caste is most thermally sensitive to heat. We found that larvae had significantly lower heat tolerance than adults, highlighting the importance of colonial thermoregulation. We then measured the energy expenditure of large colonies under acute thermal stress (5-40 °C) using flow-through respirometry while simultaneously quantifying Tn. Colonies that experienced Ta at or below optimal Tn (≤30 °C) were successful at thermoregulation. At 35 °C and above, however, Tn increased despite high energetic costs to the colony. Together our results demonstrate that high Ta poses a risk to colonies that fail to buffer thermally sensitive larvae from changes in Tn.

Bee-Plant Interaction Networks in a Seasonal Dry Tropical Forest of the Colombian Caribbean

Mutualistic interactions between bees and flowering plants have been widely recognized as one of the most important for the maintenance of these communities throughout ecosystems. Consequently, understanding how these interactions occur is highly important, especially in seasonal dry tropical forest (SDTF), one of the most endangered ecosystems in northern South America. In this study, we analyzed the changes between interaction networks across two well-defined seasons, dry and wet, in a SDTF of the Colombian Caribbean in Taganga, Magdalena. We also determined changes in species composition and their role in interaction networks. To study this system, we compared two approaches: (1) networks constructed with data from direct collections in flowering plants, and (2) networks constructed with pollen data obtained from bees' bodies. A total of 44 species were collected in 18 species of flowering plants; also, we registered 16 additional plants presented in the records only as pollen types. We found that network metrics, connectance, nestedness, specialization (H2'), and interaction strength asymmetry remain stable through seasons. However, when the two types of approximations were compared, there were significant differences. Networks constructed with pollen data are more connected, less specialized, and with lower values of interaction strength asymmetry. The major difference between seasons relied on the interacting species composition, due to a high species turnover. Bee community was more diverse in dry season. Apidae family, mainly eusocial species, persisted in the community, being more abundant and relevant in wet season. For dry season, Megachile and other solitary species from Apidae and Halictidae families were better represented and relevant for the community. We found that Fabaceae is an important resource for bees in both seasons. In addition, herbaceous species from Asteraceae and Convolvulaceae were preferred in wet season, while shrub and tree species from Fabaceae and Polygonaceae were the main resource in dry season.

'Bee hotels' as tools for native pollinator conservation: a premature verdict?

Society is increasingly concerned with declining wild bee populations. Although most bees nest in the ground, considerable effort has centered on installing ‘bee hotels’—also known as nest boxes or trap nests—which artificially aggregate nest sites of above ground nesting bees. Campaigns to ‘save the bees’ often promote these devices despite the absence of data indicating they have a positive effect. From a survey of almost 600 bee hotels set up over a period of three years in Toronto, Canada, introduced bees nested at 32.9% of sites and represented 24.6% of more than 27,000 total bees and wasps recorded (47.1% of all bees recorded). Native bees were parasitized more than introduced bees and females of introduced bee species provisioned nests with significantly more female larva each year. Native wasps were significantly more abundant than both native and introduced bees and occupied almost 3/4 of all bee hotels each year; further, introduced wasps were the only group to significantly increase in relative abundance year over year. More research is needed to elucidate the potential pitfalls and benefits of using bee hotels in the conservation and population dynamics of wild native bees.

Cavity types and microclimate: implications for ecological, evolutionary, and conservation studies

The abiotic conditions of the immediate environment of organisms are key factors for a better understanding of ecological and evolutionary processes. Yet, information in this regard is biased towards some habitat types, landscapes, and organisms. Here, we present a 2-year comparative study of the microclimatic properties (temperature, relative humidity, and their fluctuation) of three cavity types (nest boxes, cavities in bridges, and burrows in sandy cliffs) in an arid environment. We found marked and consistent months-long differences in microclimate among the three cavity types. Nest boxes were colder than the other cavity types, with temperature oscillations being an order of magnitude higher than in other cavity types. In contrast, microclimate was very stable in burrows and cavities in bridges, the former being generally warmer and drier than the latter. We also discuss the biological implications of microclimatic conditions and its variation in different cavity types by presenting two case studies, namely the temperature-humidity index and water vapor pressure during the hatching period of an endotherm and the chilling period during the diapause of an ectotherm ectoparasite. We stress the need for comparative studies of the same organisms subjected to different microclimates given the important ecological, evolutionary, and conservation implications.