California is an agricultural hot-spot of the world, producing large quantities of field crops, fruits, nuts and vegetables. In 2019 the total value of principal crops in California was over $33 billion, the second-most productive state was less than half that amount . There are estimated to be between 1,600 to 2,000 species of bees in California , of which 46 bee species within 17 genera are found commonly in Californian cities . Bees are indispensable drivers of ecosystem pollination, aiding greatly to plant reproductive success and biodiversity , the foundation of an enormous diversity of other organisms. Effective bee pollination across a variety of landscape types helps to ensure self-sustainable cities and human communities . This research focuses on the connection between plants and the attracted foraging bees. This study connects the floral landscape to pollinator foraging events taking place on it. For example, a landscape’s plant community composition is known to be a main predicting factor in the presence or absence of bees .
Many studies focus on bee foraging habitats and have tried to quantify the attractiveness of plants to bees . While plant list short-comings are part of the problem with evaluating bee habitats , french flower bucket understanding how spatial implications play out across a landscape is essential to enhance understanding of patch dynamics and the potential effects of fragmentation. As noted above, in Chapter 1 we determined that actual bee foraging preferences varied greatly from published expected foraging associations. This research builds on Chapter 1’s findings, by examining if spatial and temporal habitat usage was limited by a poor understanding of bee forage plants or not. This research study compares the smaller WHR plant selection with the full plant selection which bees used for forage in Chapter 1. By taking this approach, this research examines spatial habitat utilization and infers potential implications . The study examines whether the differences in plant palette usage made a large difference or not in utilized habitat.Habitat fragmentation, degradation and destruction are cited as the main reasons for declines in California native bee populations .
Drawing from the theories of island biogeography and metapopulation dynamics , fragmentation is defined as suitable habitat patches being too far apart to support sustainable bee populations. On an individual level fragmentation could lead to isolation, or the inability to disperse to another habitat patch for requisite resources, for example, lack of flowers . Spatial isolation of habitat patches has been found to decrease diversity of bees in urban landscapes . Even in naturalistic habitat fragments, there have been shifts of bee abundance and richness due to isolation . Overall, anthropogenic disturbances have significant negative effects on wild bees . However, in areas with less than 50% impervious surface pollinators still seem to provide sufficient pollination services to wild vegetation and crops . Currently bee life history literature does not concur on which scale of habitat fragmentation has the largest impact. For example, some studies concentrate at the entire world scale the North American continent scale , the entire United States country scale , and the smallest studies are said to be at the microsite, consisting of several point locations, several miles across , additionally, Cane et al. compared bee ecological characteristics such as dietary breadth.
Most of the above mentioned research focused more on European honey bees, though studied less often native bees were included in some studies. There are landscape elements which are completely inhospitable to bees and can be defined as habitat destruction, for example: paved surfaces and the footprint area buildings use . Habitat degradation to bees consists of detrimental changes of a site. For example, a dramatic shift in vegetation cover of a formerly naturalistic site will have effects on the bees which utilized the former floral resources. Bees’ responses to such shifts will vary , as their foraging habits, obligate versus generalist, are similar to butterflies in California . In terms of foraging some bees have benefitted from predominantly human shaped and dominated landscapes , while other bees decline . Habitat gaps may also occur temporally, depending on plant phenological patterns, leading to patch isolation or connectivity . Bee foraging preferences, whether polylectic or oligolectic , can also be an origin of habitat fragmentation if a landscape is not suitable. For bees, if sufficient floral resources are not available, that represents a non-foraging area, possibly a population sink. This phenomenon may lead to ecological filtering, reducing bee diversity . Current bee foraging plant lists have limitations in their ability to predict a bee genera’s presence or absence . Nevertheless, measuring bee-to-flower associations is a starting point to understanding the potential that there is habitat fragmentation for bees. Identification of the most basic levels where and when habitat fragmentation occurs is essential to determine before conservation remedies can be prescribed. It is essential to investigate these spatial problems with geographic tools to aid in bee conservation using empirical relationships with which bees experience their world.Bees vary widely in their foraging distance ability from a nest . Bee body size has been shown to be an indicator of forage diameter radii . Based on published body size data , bees may forage up to 2 mi maximum for only European honey bees, 1 mi for large bodied bees such as Bombus and Xylocopa, mid-sized bees are most common and average 0.25 mi , and the smallest bees are estimated at only 0.11 mi from their nests . Bee foraging radii is traditionally measured by the distance between a bee’s nest and its foraging range . However, determining individual nesting locations for solitary native bees is extremely difficult and not attainable or reliable based on current bee research studies , often taking a long time and often not gleaning results quickly enough for this research spatial scale and quantity of data . Given the intractability between locating nests of individual bees observed foraging in gardens, a general assumption is made in this study that foraging instances are relatively closely linked in proximity to nest locations, and therefore the foraging data points are used as a proxy for nesting locations. These foraging radii are for female bees, bucket flower which create and care for nests, rather than males, which utilize the landscape differently . Importantly, maximum foraging ranges represent an extreme limit on travel, as most individual bees will not travel as far as the maximum . In traditional meta population literature, differences between home range movement versus individual dispersal have been studied with more charismatic animals , but these movement dynamics have not been studied thoroughly in relation to bees. Among the limited extant bee dispersal research studies, results align with previously cited research regarding bee body size, degree of host plant specialization and bee sociality .The human landscape’s horticultural gardens can be florally diverse, contributing to an array of potential habitat types for bees . Furthermore, bee foraging preferences are not well understood, but are crucial to mitigate pollinator population declines . Thus, the role that horticultural garden conditions can contribute to increasing bee population numbers needs to be identified. Conversely, horticultural conditions which provide little to no benefit to bees should also be identified and avoided or discouraged. Studies conducted thus far have indicated a variety of responses of bees to managed landscapes, including both increased bee richness in some anthropogenic sites or some have shown decreased bee diversity in anthropogenic sites . However, overall, many land use activities are known to be detrimental to bee communities . Conversely, habitat simplification is known to have a negative effect on bee populations . Furthermore, plant community composition across a spatial gradient has been reported to have an effect on plant-pollinator resilience as a whole .
Therefore, it is important to assess both composition and configuration ofanthropogenic landscapes to determine why pollination ecosystem services occur in greater or lesser frequency across the landscape . Floral abundance, richness and spatial distribution have been noted to affect native bee communities , but the effect of these variables needs to be explored in more detail, and across a larger variety of garden types. Presence of weeds seems to enhance bee presence as well . Overall, bees respond differently to anthropogenic conditions and it is essential to study the variety of responses to maximize conservation efforts . Overall, current habitat remedies involve providing adequate floral resources and increasing floral diversity . Reconciliation ecology, a conservation science technique used in human dominated habitats , has been promising for other organisms and is highly applicable for bees.In recent years, scientists have used the term “Anthropocene” to describe the current geological epoch which by definition states how far humans have influenced Earth’s global biogeochemistry. Similarly, at the landscape scale, humans have dominated and changed Earth’s terrestrial ecosystems dramatically, leading to the term “anthroscape” . Notable in recent times, our infrastructure often excludes wildlife and represents an ecological sink or void. For example, paved roads offer no value to bees. Buildings and their footprints aid in reducing viable bee habitat. Notably, some horticultural planting schemes may represent opportunities to bees. Waterways, ponds, pools represent sinks to nearly all bees, the exception being Apis melifera which has low tolerance for critical water content and need fresh water to survive whereas native California bees have very high tolerance for critical water content and do not need fresh water bodies regardless of being in urban or rural ecosystems . The degree to which bees living in human-dominated areas act as source habitats to adjacent landscapes should be explored further.This research study aims to pinpoint when and where various bee genera experience habitat patch dynamics versus habitat fragmentation . Though bee and flower phenology are discussed at length in the literature, it has not been formally explored from an explicitly spatial perspective at the landscape scale. As such, this is the first study to document bee habitat spatial and temporal dynamics providing important novel insight for future bee conservation efforts or further studies in bee habitat fragmentation. The main research questions covered in this paper include: What constitutes a gap in native bee pollinator habitat? How do bees’ annual spatial patterns of potential versus realized habitat function over a year? How can bee foraging maps be used to conduct conservation gap analysis at a local scale? How do partial and full WHR plant palettes compare in terms of habitat modeling for bees? and, What are the implications of this research for bee habitats?To help solve these complicated topics, the wildlife-habitat relationship models developed for bees in Chapter 1 are used here to spatially estimate and measure gaps in bee genera pollination networks. The spatial analyses presented in this study shed light on the degree of real-world bee habitat fragmentation. Monthly observed bee georeferenced data which were compiled in Chapter 1, are here analyzed via GIS maps. Seasonality of both bees and flowers were integrated in the mapping model analysis in an effort to identify where and when bee potential habitat gaps and potential fragmentation might occur The spatial distribution patterns of suitable, insufficient, or unsuitable habitat for bees are still poorly understood, yet essential to understand for native bee conservation purposes. This study investigates if bee foraging maps can be used to conduct both spatial and temporal habitat gap analysis.The UC Davis Arboretum and Public Garden , located in California’s Central Valley, is a unique environment to study bee patch dynamics and potential habitat fragmentation. The curated plant collection is fully mapped and contains 35 gardens along the linear Arboretum landscape . Each themed garden has a distinct geographically defined border, and plants are identified/labeled to the plant species, subspecies, or cultivar level. Arboretum maps are spatially accurate within two meters .Computer geographic information systems technology, using ArcGIS version 10.7.1 , was employed to investigate and calculate where and when habitat gaps occur for bees in the anthroscape. The theoretical framework was based on wildlife-habitat relationships conservation science modeling . In Chapter 1, monthly WHR foraging models were developed for each bee genus observed in the Arboretum. This chapter applies the predictive foraging models spatially, using the Arboretum’s geodatabase of mapped plants. Using this approach, a GIS predictive bee foraging model was developed and tested on-site with fieldwork to verify and quantify differences .