Windows of opportunity and the temporal structuring of foraging activity in a desert solitary bee

Abstract

Summary 1. Females of the desert solitary bee Anthophora pauperata collect nectar and pollen almost exclusively from Alkanna orientalis (Boraginaceae). The bee and plant are found together in the early spring, living in the bottom of steep‐sided wadis (dry river valleys) at an altitude of 1500 m in Egyptian Sinai. 2. Female A. pauperata showed clear morning and afternoon peaks in foraging activity, separated by a 2–3 h midday period spent in their underground nests. This study analyses the following in order to identify the factors structuring this daily pattern: thermal aspects of the bee and its environment, temporal patterns of resource provision by the plant, and female nectar and pollen foraging behaviour. 3. Although A. pauperata can generate substantial heat endothermically, morning and evening ambient temperatures well below 10 °C defined a thermal window within which foraging occurred. Maximum air temperatures were moderate (25–30 °C), and examination of the physiology and behaviour of A. pauperata suggests that the midday reduction in flight activity was not due to thermal constraints. 4. Alkanna orientalis produces protandrous hermaphroditic flowers. Female A. pauperata collected pollen from male‐phase flowers and harvested nectar preferentially from female‐phase flowers. Although the nectar standing crop was relatively constant throughout the day, pollen availability peaked strongly in the early afternoon. 5. Female A. pauperata visited young male‐phase flowers as soon as they opened, generating an early afternoon peak in pollen foraging activity and depleting the pollen standing crop rapidly. A morning peak in pollen foraging occurred when females gleaned remnant pollen from flowers that had opened the previous day. Pollen availability in the morning was far lower than in the early afternoon, and the time taken to collect a full pollen load in the morning was significantly longer. Collection of pollen in the morning despite very low resource availability suggests that pollen may be a limiting resource for A. pauperata. 6. In contrast to many existing examples of bimodal activity patterns in highly endothermic bees, the bimodal activity patterns of female A. pauperata appear to be driven not by thermal considerations but by daily patterns of pollen release from its principal food source.

Diverse pollinator communities enhance plant reproductive success

“…Furthermore, diversity effects in pollination may be owing to a diverse plant community being pollinated (corresponding to resource heterogeneity) [19] or to differences among pollinators visiting a single-plant species [21,30]. The latter can occur, for example, when different species in a pollinator community partition their foraging activities during different daytimes [31] or among flowers at different positions within plant individuals [16]. However, experimental knowledge of the functional consequences of pollinator niche partitioning in diverse pollinator communities for the pollination success of single-plant species is currently lacking [but see 22].…”

Environmental windows for foraging activity in stingless bees, Melipona subnitida Ducke and Melipona quadrifasciata Lepeletier (Hymenoptera: Apidae: Meliponini)

“…This difference concerning the thermal window between the two meliponine species is presumably related to the bees' physiological adaptations to the climatic situation of their respective natural habitats. Here, a critical factor is the absolute physiological limit of bees, determined by the temperature below which endothermic heating of the flight muscles becomes uneconomic (Heinrich, 1993;Stone, 1993;Stone et al, 1999 (Silva & Pinheiro, 2007). In contrast to M. quadrifasciata, M. subnitida initiated foraging in July and August not before 8:30 am.…”

“…In addition to this direct influence of climatic factors, primarily of ambient temperature, on the foraging activity of a species, climatic factors affect the flowering phenology of plants and, consequently, the availability of floral resources for the bees. Hence, the foraging success of a bee species is restricted to an environmental window (EW), a combination of optimal ambient temperatures and resource availability (Stone et al, 1999;Hilário et al, 2000). Mismatches between flowering and optimal foraging temperature may lead to a dramatic reduction of a colony's food intake and, eventually, of brood production, which depends on the availability of resources within the nest (Ribeiro et al, 2003;Ferreira-Junior et al, 2010).…”

“…Given the necessity of an accurate match between resource availability and foraging temperature (Stone et al, 1999), the breadth of the environmental window of a bee species is determined by its capacity to acclimate to different abiotic conditions, the range of temperatures at which foragers may be active, and the dietary niche breadth. Due to the bigger amplitude of foraging possibilities, the foraging success of species with broad EWs, such as the honey bee Apis mellifera Linnaeus (Apidae, Apini), is bound to be less affected by variations in the abiotic and biotic environment than that of species with narrow EWs.…”

Patterns in diurnal co-occurrence in an assemblage of hoverflies (Diptera: Syrphidae)

“…In particular, we hypothesized differences in the patterns of diurnal species co-occurrences due to the interplay of factors related to the availability of floral resources (e.g., daily timing of flower opening) and species biology (e.g. thermal physiology, sexual interactions and nesting cycles) (Willmer, 1988;Stone et al, 1999;Willmer & Stone, 2004) In addition, we tested for gender differences in patterns of species assemblages. Distinct patterns in the inter-specific relations between genders can be expected due to differences in their reproductive biology and dietary requirements.…”