Competition from honey bees on wild bees

1. Competition from honey
bees on wild bees
- effects, knowledge gaps and interventions
SANDRA LINDSTRÖM, CENTRE FOR ENVIRONMENTAL AND
CLIMATE SCIENCE

2. Status and trends for wild bees
• 1/3 of the 299 wild bee species is on the swedish red-list
• Indications that many species' populations are declining nationally
- Ranges are greatly reduced
• Specialists are over-represented
• Arable and urban landscapes
• Several causes, lack of forage potentially one
(Borgström m.fl. 2018. Pollinatörer och pollinering i Sverige – värden, förutsättningar och påverkansfaktorer. Naturvårdsverket)

3. Number of honey bee hives
(Potts m.fl. 2010. Journal of Apicultural Research)
(IBPES 2016 chapter 3)
Year 2019: 160 000-170 000 honey bee hives in Sweden
(SJV, 2019. Det ekonomiska värdet av honungsbin i Sverige)
2019

4. Food resource competition
(Mallinger et al. 2017)
When does competition between bees
have negative effects on the long-term
development of populations?

5. (Kleijn et al. 2018, Science)
Bees have a lot in common
-
Joint efforts to benefit the bees have
greater potential to be successful!

6. Records identified in
data base search:
(n=891)
Title and abstract
screening
(n=875)
Full-text screening
(n=609)
Exkluded records,
based on criteria
(n=266)
Exkluded records,
based on criteria
(n=549)
Duplicates excluded
(n=14)
For analysis
(n=57)
European empirical
records
(n=33)
Systematic map of the
European empirical
evidence

7. NO
IMPACT
Wild bees
Honey bees
Floral resource
overlap
Unchanged wild
bee visitation
rate
Reduced wild
bee visitation
rate
Unchanged
resource
harvest
Reduced
resource
harvest
Alternative
floral
resource
Reduced
survival
Reduced
fecundity
Reduced
population
size/extinction
NEGATIVE
IMPACT
(Following Fig. 1 in Paini et al. 2004)
Competition mechanisms

8. Empirical evidence for competition
• 24 reviews & 33 empirical European studies
- Floral resource overlap
- Effects on foraging and resource intake
- Effects on densities and diversity
- Effects on reproduction and survival
Negative effects shown on several aspecs of wild bees resources, foraging and
abundance.
Lack of strong evidence on effects on reproduction, survival and populations.

9. Empirical findings
Critical levels of honey bees:
Few studies, depends on flower resource availability.
Modifying factors:
A few studies on landscape character and flower resource availability.
Sensitive species and species traits.

10. Number of wild bee species that has foraging
overlap in % with honey bees in intervals of 10
Rasmussen C, Dupont YL, Madsen HB, Bogusch P, Goulson D, et al. (2021) Evaluating competition for forage plants between honey bees and wild bees in Denmark. PLOS ONE 16(4): e0250056.
https://doi.org/10.1371/journal.pone.0250056
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0250056

11. Competition from a Swedish perspective
• Generally low densities of honey bees (0,4 honey bee hives per km2)
• Average European density (4,2 honey bee hives per km2)
• But ~70% of the Swedish honey bee hives is in the south of Sweden
• Batavsandbi Andrena batava, fältsandbi A. morawitzi are oligolectic
on sälg Salix and red-listed species.
• A danish study identified that the red listed bees Vialsandbi Andrena
lathyri, monkesolbi Dufourea halictula, klocksolbi Dufourea inermis,
stengnagbi Hoplitis anthocopoides guldbyxbi Dasypoda suripes had
very large (>90%) overlap with honey bees. (Rasmussen et al. 2021)

12. Potential interventions
Suggestions:
- Increase floral resources (no studies)
- Adjust the distance to protected areas (Henry & Rodet 2020)
- Adjust densities or avoid honeybees in protected areas
- Apply the precautionary principle in areas with threatened wild bee species (Mallinger et al. 2017)
- or threatened wild bee species with high overlap with honey bees (Rasmussen et al. 2021)
Evaluation tools:
- “HUM” – Hive units monthly (Cane & Tepedino 2017)
- Parameterized models (Sörensen et al. 2020)
- “AIR” – Apiary Influence Range (Henry & Rodet 2020)

13. Knowledge gaps
• More studies on reproduction and survival are needed for more species
• Context dependent effects
- Honey bee distances and densities
- Floral resource availability
- Networks of wild bees and plants
- Spatial and temporal scales
- Interactions with nest sites
- Interaction with other stressors, e.g. pesticides
• What regulates bee populations? How important is competition in relation to other
threats?

14. Summary
• Plenty of studies relating to food choices and abundance
- mixed effects
• Few studies examine effects on reproduction - the
knowledge gaps are large
• Long-term effects studies - completely missing
• Species specific studies – lacking
• Correlative studies – weak evidence
• WANTED: Experimental, well-replicated studies with
controls, several levels of honey bee densities and
floral resources measuring reproduction.

16. Extra slides

17. Photo: Mårten Sjöbeck. 1934… … 90 years later
Spjutstorp 1940 Spjutstorp 2014
Altered landscapes

18. Nectar availability in relation to bumble bee needs over the season
on four british farms
Journal of Applied Ecology, Volume: 56, Issue: 7, Pages: 1585-1596, First published: 19 April 2019, DOI: (10.1111/1365-2664.13403)

19. Heterogeneous landscape
Small scales
More flowers
Short distances between nest-sites and flowers
More homogenous landscape
Larger scale
Fewer flowers
Longer distances between nest-sites and flowers