Landscape structure and climate seasonality affect the amount, richness and diversity of pollen collected by honeybees in a Neotropical region of Colombia

Pollen is the main food for honeybee broods and young workers and so colony development and reproduction rely heavily on pollen availability, both spatially and temporally, in the environment. Intensification of agriculture and climate seasonality are known to alter honeybee foraging patterns and pollen intake through changes in resource availability in temperate regions; however, little is known about how honeybees respond to such environmental factors in tropical regions. Pollen species collected by honeybees in a Neotropical agricultural region of Colombia were identified. The effects of landscape structure (landscape Shannon Diversity Index, forest area in 1000 m around the apiary) and climate seasonality (mean monthly precipitation) on the amount, richness and diversity of pollen collected by the honeybees were evaluated for all pollen species together and pollen species segregated according to forest and anthropic areas (croplands, grasslands, woodlands, urban areas). Honeybees were found to be much more associated with anthropic than forest pollen species regardless of landscape structure or precipitation. However, the amount, richness and diversity of pollen from all species and forest species responded positively to landscape diversity and forest area, suggesting an advantage for honeybees in obtaining small quantities of pollen from forest species, in spite of being well-adapted to forage in anthropic areas. Precipitation was found not to be related to the overall amount and overall richness of pollen collected by honeybees, suggesting that climate seasonality was not an important factor for pollen foraging. Nonetheless, overall pollen diversity was negatively affected by precipitation in less diverse landscapes, while anthropic pollen diversity was negatively affected in more forested landscapes. These findings are compared with those from temperate regions, and the implications for honeybee productivity and survival, and their interactions with Neotropical native species, are discussed.


Introduction
Pollen is essential for the development and sustainment of honeybee colonies 47 because it provides the proteins necessary for the development of broods and young 48 workers [1]. The quantity and quality of pollen acquired by honeybees positively influences 49 their health and survival by improving their longevity and immune function [2,3]. 50 Therefore, understanding the factors that affect honeybee pollen intake and foraging 51 patterns is fundamental to enhancing their well-being and productivity. 52 Honeybees select among different pollen species according to their abundance in 53 the surroundings, their attractiveness and the ease of collection and handling [4,5]. In spite 54 of this selectivity, however, honeybees forage on diverse resources, including some that are 55 not particularly attractive or efficiently gathered, in order to fulfill the great pollen demands 56 required for successful colony development and reproduction (~20 kg year) [6], and to 57 obtain different nutrients that may be segregated among plant species [2,7]. Given such 58 great pollen requirements, the amount and diversity of pollen collected by honeybees are 59 expected to vary in response to changes in pollen availability due to agricultural 60 intensification and flowering periods that are driven by climate seasonality. However, 61 contradictory results have been found regarding the relationship between the amount and 62 diversity of pollen and landscape structure in temperate agricultural regions [7,8,9, 10, 4 63 11], as honeybees seem to compensate for resource scarcity by increasing foraging 64 distances to obtain sufficient quantities of diverse pollen for their colonies [10,11,12,13]. 65 However, temporal resource shortages resulting from flowering seasonality have also been 66 found to considerably impact honeybee colony survival, especially in cases of landscapes 67 with low diversity where pollen availability cannot be compensated for by extending 68 foraging range [2, 10, 11]. 69 How honeybees use pollen resources among different spatial and temporal 70 conditions in tropical regions has been barely studied. Most such studies have been local 71 and descriptive and, to the extent of our knowledge, there has been no study that explicitly 72 related landscape structure and climate seasonality to the amount, richness and diversity of 73 pollen collected by honeybees. This issue is of particular concern in the Neotropics, where     comprise 95% of total pollen amount and were found in more than 10% of pollen samples.

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The overall pollen amount collected by honeybees mainly corresponded to 180 anthropic species (Fig 2a), and was positively related to forest area (explained variance =   Response variables were the amount, richness and diversity of pollen from species in the 207 overall landscape, and from species segregated as from forest areas and from anthropic  Overall pollen richness was dominated by anthropic species (Fig 2b) and was 221 explained by forest area (explained deviance = 0.14, p = 0.002, Fig 3d).  Fig 3f). Anthropic 225 pollen richness was not explained by any of the studied variables.

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The most important anthropic species (i.e., Brassicaceae Type, Trifolium species apiaries, as originally predicted (Fig 3a, d, g). These results suggested an advantage for total land cover (Fig 4a), seemingly corroborating the idea that honeybees rely principally 277 on anthropic species even when forest species could represent an additional advantage.

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Regarding climate variability, no relationship was found between precipitation and 291 the amount of pollen collected by honeybees (Fig 3c), probably because monthly Nonetheless, a negative effect was found for precipitation on the richness of pollen from 298 forest species and the diversity of pollen from all species (Fig 3f, i) As with the effect on overall pollen diversity, pollen diversity from anthropic 316 species was found to be positively related to precipitation (Fig 3i), although the interaction 317 between precipitation and forest area showed that the increase in anthropic pollen diversity 318 occurred just in landscapes with small forest areas (Fig 4c), where the availability of 319 anthropic cover types was probably sufficient to provide more diverse anthropic species. In 320 contrast, anthropic pollen diversity in forested landscapes tended to decrease, probably 321 because smaller anthropic areas hindered pollen gathering on diverse anthropic resources.

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In conclusion, we found that honeybees in this Neotropical region were especially