Pollinators and Agroecology: new research directions for 2014

A lot of great research on wild pollinators and agroecosystems has been published this year. In particular, the pollinator conservation literature seems to be moving on from simple abundance/richness comparisons to other ecological contexts that are potentially more relevant to policy and management decisions, such as nutritional and commercial qualities of insect-pollinated fruits.

Below is nice round list of four articles published this year that got me excited. All four are ‘firsts’ for their particular topics and use great study design and insight to lead current knowledge on the subject matter gently in a new direction. They are also pertinent reading as we balance on the cusp of the UN’s international years of Family Farming and Soils.

Nesting habitats for wild bees

Sardiñas & Kremen. ‘Evaluating nesting microhabitat for ground-nesting bees using emergence traps.’ Basic and Applied Ecology

Background: Wild bees are critical to ecosystem function, but we still know very little about one of their keystone resources, nesting substrates. Only about 15% of bee species nest in cavities, and they certainly benefit from all the great trap nests being installed in farms and gardens. Most of the rest of the world’s bees nest in the ground. Nesting resources have only recently been acknowledged to influence wild bee community composition, persistence and response to disturbance. From previous studies and observations we know the basics of nest substrate 101, but ground nests are obviously more challenging to locate than cavity nests and so are understudied. Where researchers have considered ground nesting resources when sampling bees with other methods, they often only consider nesting substrates in the system based on known preferences, rather than known nesting locations (I did this myself in my paper on keystone resource availability in almond plantations).

Results: The authors used emergence traps to sample bees emerging from ground nests in Californian chaparral pine habitat (a Mediterranean habitat similar to Australian mallee habitats). They compared samples from the emergence traps with bee samples caught with pan traps and sweep netting at the same locations and looked at bee-habitat relationships. A total of 54 species were caught across all samples and only 4 species were shared by all three sampling methods. Fewer native bees were collected in emergence traps placed on soil that was compacted, contained pre-existing holes, and had a slope less than 30°.

Key messages:

Multiple sampling methods are better where studies are focused on overall species richness or inventories of species using a particular habitat.
Negative relationships between bee communities and compacted soil and flat ground show that ground nesting bees will be less likely to build nests where intensive management has compacted and flattened the soil surface – a common occurrence in agricultural and urban systems.

Best quote: These kinds of direct, rather than correlative, studies are necessary to assist in conserving and promoting ground-nesting bee populations in natural and managed landscapes.

Resource diversity for pollinators

Drescher et al. ‘Diversity matters: how bees benefit from different resin sources.’ Oecologia. (Also see my F1000 recommendation with Gary Luck for this article)

Background: Wild bees need resource diversity, but few studies have looked beyond the obvious – flowers. Resin is a crucial resource for many bee species, particularly the social stingless bees. Resins are used by many bees as a nest building material. Stingless bees also incorporate chemical compounds from the resins into their body’s chemical signals. These chemicals are used for communication and defence, and so ultimately influence colony fitness.

Results: The authors collected plant resins from native plants known to be major sources of resin for stingless bees in the study area. Through lab-based behavioural trials and microbiological assays, they tested for repellent effects on common predators, parasites and pathogens of bee colonies for each individual resin and resin mixtures. Repellent effects varied between resin concentrations and test groups, but a mix of all resins had a stronger repellent effect on the small hive beetle, a parasite of stingless and honey bee colonies, than any of the individual resins tested alone. Repellent effects were also found on some pathogens and a predatory meat ant.

Key messages:

New insights for biology and ecology. Resin diversity has rarely been considered as a key influence on wild bee communities, so this study is a first in that regard. Also, the study region, the Sunshine Coast in Queensland (my own home range!), is a rarely studied ecological wonderland.
Survival of individual bees, and their colony, can depend on the availability of diverse resins in the bee’s home range. What if they live in a landscape dominated by monoculture resin sources, such as pine plantations?
Pollinators rely on many other resources besides flowers, and it is critical for pollinator management and research to consider the diversity and distribution of multiple resources across a pollinator’s life cycle.

Best quote: Our results [stress] the importance of not only resin collection itself but also the availability of various resin sources within the foraging range of bee colonies, which is likely reduced in the highly agricultural areas of many industrialized countries.

Conservation in agroecosystems

Gonthier et al. ‘Biodiversity conservation in agriculture requires a multi-scale approach.’ Proceedings of the Royal Society B

Background: Although hundreds of studies have looked at local or landscape effects on different wildlife groups using farmland, most have focused on one species group and generally only consider either landscape or local factors, not both. This much-needed synthesis compares results from studies that look at both factors within the same system, in an attempt to identify patterns useful for management.

Results: Low-intensity farms mostly had higher abundance and richness of wildlife species than high-intensity farms. However, plant richness responded more strongly to local management practices than insect or vertebrate (birds & animals) richness did. For landscape factors, on-farm abundance and species richness also increased with landscape complexity. However, at this scale, insect and vertebrate richness were positively related to landscape complexity, while plant richness was not.

Key messages:

This may seem like common-sense, but a broad-scale synthesis of all these results has not been published before, so this article is good news for science-based policy and management decisions.
Everything has a context and ‘one size fits all’ policies are not realistic for balancing conservation and production in agroecosystems. Multi-scale approaches and long-term regional planning need to be coupled with local management changes.

Best quote: ..our results suggest that the losses of species in agricultural plots owing to local management and landscape-level intensification are very often associated with the loss of beneficial invertebrate diversity.

Sustainable yields

Ponisio et al. ‘Diversification practices reduce organic to conventional yield gap.’ Proceedings of the Royal Society B

Background: The organic vs conventional agriculture debate has been going for decades. Many pro-conventional arguments claim that organic agriculture produces lower yields, so is not a realistic option for addressing growing food demands. Previous meta-analyses that have attempted to identify yield gaps between the two kinds of agriculture have come up with varying results.

Results: Overall, organic yields were 19.2% lower than conventional yields, a smaller yield gap than that found in previous analyses. However, the yield gap varied considerably across crop types and management practices. Within individual groupings of crop types and management practices, some yield gaps were smaller. Over-representation of some crops and systems in the comparison studies also affects the overall average – cereal crops were the focus of 53% of the studies the authors found, and these crops show the greatest difference in yield between organic and conventional agriculture, partly because of more historical investment in breeding high-yielding cereal varieties for conventional ag. Yield gaps dropped to 8-9% when farm diversification practices (rotations, multi-cropping) were used in both agriculture types.

Key messages:

Perfect example showing how relying on ‘overall’ averages can potentially misinform policy and management decisions.
Agroecological and socio-economic research is needed to address yield gaps. This can be done by focussing on how specific management practices (e.g. multi-cropping, rotations, biocontrol etc.) can be used in different crop types to address the yield gaps, rather than the unrealistic ‘organic vs conventional’ argument.

Best quote: … environmentally sustainable, resilient production systems will become an increasingly urgent necessity in a world where many planetary boundaries have already been reached or exceeded.