Human‐mediated species introductions provide real‐time experiments in how communities respond to interspecific competition. For example, managed honey bees In this study, we investigate impacts of increasing honey bee abundance on native bee visitation patterns, pollen diets, and nectar and pollen resource availability in two Californian landscapes: wildflower plantings in the Central Valley and montane meadows in the Sierra. We collected data on bee visits to flowers, pollen and nectar availability, and pollen carried on bee bodies across multiple sites in the Sierra and Central Valley. We then constructed plant‐pollinator visitation networks to assess how increasing honey bee abundance impacted perceived apparent competition (PAC), a measure of niche overlap, and pollinator specialization (d'). We also compared PAC values against null expectations to address whether observed changes in niche overlap were greater or less than what we would expect given the relative abundances of interacting partners. We find clear evidence of exploitative competition in both ecosystems based on the following results: (1) honey bee competition increased niche overlap between honey bees and native bees, (2) increased honey bee abundance led to decreased pollen and nectar availability in flowers, and (3) native bee communities responded to competition by shifting their floral visits, with some becoming more specialized and others becoming more generalized depending on the ecosystem and bee taxon considered. Although native bees can adapt to honey bee competition by shifting their floral visits, the coexistence of honey bees and native bees is tenuous and will depend on floral resource availability. Preserving and augmenting floral resources is therefore essential in mitigating negative impacts of honey bee competition. In two California ecosystems, honey bee competition decreases pollen and nectar resource availability in flowers and alters native bee diets with potential implications for bee conservation and wildlands management.
Pesticides and parasites have each been linked to increased mortality in western honey bees ( Here, we use a hierarchical meta‐analysis of 63 experiments from 26 studies to gain a clearer view of the combined effects of parasites and pesticides on honey bee health. We found that combined pesticide–parasite treatments do tend to be deadlier than uncombined treatments but are significantly less deadly than predicted additive or multiplicative effects. In other words, combined treatment effects are not synergistic, but antagonistic. Much of the previous uncertainty about the combined effects of pesticides and parasites on honey bee health can be attributed to a bias in the previous research against stressor antagonism; many researchers have excluded the possibility of antagonism a priori.
- Award ID(s):
- 1744552
- PAR ID:
- 10435724
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Applied Ecology
- Volume:
- 58
- Issue:
- 5
- ISSN:
- 0021-8901
- Page Range / eLocation ID:
- p. 997-1005
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Evidence of exploitative competition between honey bees and native bees in two California landscapesmore » « less
Abstract Apis mellifera (L.) have been widely introduced outside their native range and may compete with native bees for pollen and nectar. Indeed, multiple studies suggest that honey bees and native bees overlap in their use of floral resources. However, for resource overlap to negatively impact resource collection by native bees, resource availability must also decline, and few studies investigate impacts of honey bee competition on native bee floral visits and floral resource availability simultaneously. -
more » « less
Abstract Pollinators are introduced to agroecosystems to provide pollination services. Introductions of managed pollinators often promote ecosystem services, but it remains largely unknown whether they also affect evolutionary mutualisms between wild pollinators and plants.
Here, we developed a model to assess effects of managed honey bees on mutualisms between plants and wild pollinators. Our model tracked how interactions among wild pollinators and honey bees affected pollinator and plant populations.
We show that when managed honey bees have a competitive advantage over wild pollinators, or a greater carrying capacity, the honey bees displace the wild pollinator. This leads to reduced plant density because plants benefit less by visits from honey bees than wild pollinators that coevolved with the plants.
As wild pollinators are displaced, plants evolve by increasing investment in traits that are attractive for honey bees but not wild pollinators. This evolutionary switch promotes wild pollinator displacement. However, higher mutualism investment costs by the plant to the honey bee can promote pollinator coexistence.
Our results show plant evolution can promote displacement of wild pollinators by managed honey bees, while limited plant evolution may lead to pollinator coexistence. More broadly, effects of honey bees on wild pollinators in agroecosystems, and effects on ecosystem services, may depend on the capacity of plant populations to evolve.
-
more » « less
Abstract Most pesticide research has focussed on risk to managed honeybees, but other managed and wild bees are also exposed to pesticides. Critically, we know little about the magnitude and sources of risk to honeybees compared with other bees during crop pollination.
To compare pesticide exposure and risk across wild and managed bees, we sampled the main bee groups present during bloom in 20 apple orchards, including managed honeybees (
Apis mellifera ), managed bumblebee workers (Bombus impatiens ), wild mining bees (Andrena spp. andAndrena [Melandrena] spp.), bumblebee foundress queens (Bombus impatiens ) and eastern carpenter bees (Xylocopa virginica ). We screened all bees for 92 pesticides and computed a Risk Quotient using available toxicity data (honeybee LD50s), adjusting for differences in toxicity known to scale with body mass. To gain insight into exposure origin, we compared residues in bees to those in focal orchard apple and dandelion flowers.Nearly all bee samples contained pesticides (95%), with the average contamination level ranging from 7.1 ± 2.8 parts per billion (ppb) in
B. impatiens workers to 388.4 ± 146.2 ppb inAndrena . Exposure profiles were similar for all bees exceptA. mellifera , whose unique exposure profile included high levels of the neonicotinoid insecticide thiamethoxam.All bee groups except wild
B. impatiens queens had at least one sample exceeding a US Environmental Protection Agency or European Food Safety Authority exposure level of concern.Apis mellifera experienced significantly greater risk than other bee groups, with 63% and 81% of samples exceeding an acute or chronic exposure level of concern, respectively. Risk to honeybees was driven primarily by high thiamethoxam levels not found in focal orchard flowers and likely originating outside the orchard.Synthesis and applications : We find that pesticide exposure and risk differ between honeybees and other managed and wild bees during apple pollination. Furthermore, pesticide exposure is a landscape‐scale phenomenon and therefore measures to reduce exposure must consider the surroundings beyond focal farms. Limiting orchard sprays, while reducing on‐farm exposures, will not protect far‐foraging bees from off‐farm exposures such as thiamethoxam, which we hypothesize is coming from nearby seed‐treated corn fields planted during apple bloom. -
Abstract Honey bees are critical pollinators in ecosystems and agriculture, but their numbers have significantly declined. Declines in pollinator populations are thought to be due to multiple factors including habitat loss, climate change, increased vulnerability to disease and parasites, and pesticide use. Neonicotinoid pesticides are agonists of insect nicotinic cholinergic receptors, and sub-lethal exposures are linked to reduced honey bee hive survival. Honey bees are highly dependent on circadian clocks to regulate critical behaviors, such as foraging orientation and navigation, time-memory for food sources, sleep, and learning/memory processes. Because circadian clock neurons in insects receive light input through cholinergic signaling we tested for effects of neonicotinoids on honey bee circadian rhythms and sleep. Neonicotinoid ingestion by feeding over several days results in neonicotinoid accumulation in the bee brain, disrupts circadian rhythmicity in many individual bees, shifts the timing of behavioral circadian rhythms in bees that remain rhythmic, and impairs sleep. Neonicotinoids and light input act synergistically to disrupt bee circadian behavior, and neonicotinoids directly stimulate wake-promoting clock neurons in the fruit fly brain. Neonicotinoids disrupt honey bee circadian rhythms and sleep, likely by aberrant stimulation of clock neurons, to potentially impair honey bee navigation, time-memory, and social communication.more » « less
-
more » « less
As native bee populations decrease, there is a need to better understand their nutritional requirements to sustain healthy pollinator populations. A common native bee to eastern North America is the small carpenter bee,
Ceratina calcarata . Previous studies have shown that the primary pollen sources forC. calcarata consist of clover and rose.The aim of this study is to compare the effects of diet composition on body size, development and survival. Artificial pollen diets were created using five different ratios of commercially available clover and rose pollen.
Diets containing higher ratios of clover pollen produced larger individuals with increased survival rates and faster development times. To examine this further, the macronutrient profiles of clover and rose pollen were characterised comparing: protein, sugar, fatty acid, and amino acid content. Results indicated that rose pollen contained significantly higher protein and sugar content, while clover pollen had higher concentrations of essential amino acids. These are crucial to bee health and development, which helps to explain the increased survivorship observed on high clover diet treatments.
Taken together, these results show that clover pollen provides a higher quality diet for larval development and survival of the native small carpenter bee. This research indicates that diet has a significant effect on the health of the native pollinator community and more research is needed to further explore the balance between pollen quality and availability, including essential macronutrients and the availability of these floral sources for wild bees.
