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Estimated nests in each plot and associated mean detection probability from closed population models, based on model M0 after different numbers of visits to each plot. Points represent median estimates from Bayesian posterior distribution; lines denote associated 95% credible intervals
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For bumble bees and other social organisms, colonies are the functional unit of the population rather than the individual workers. Estimates of bumble bee nest density are thus critical for understanding population distribution and trends of this important pollinator group. Yet, surveys of bumble bee nests and other taxa with sessile life stages ra...
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Citations
... As insects are small and often highly mobile, they can be challenging to detect, potentially impacting inferences made from monitoring (Dennis et al., 2017;Dorazio et al., 2011;Iles et al., 2019;Loffland et al., 2017;M'Gonigle et al., 2015;MacIvor and Packer, 2016;van Strien et al., 2013;Woodcock et al., 2016). For example, failure to observe a species at a site when it is present, known as imperfect detection (Guélat and Kéry, 2018), often results in underestimating the true occurrence of a species (Guélat and Kéry, 2018;Kellner and Swihart, 2014;Kéry and Schmidt, 2008). ...
... To build our MSOM, we used encounter histories (detection or non-detection at a site) for each species from temporal replicates, as well as covariates to account for heterogeneity in occupancy and detection. We defined occupancy as "used for foraging", thus an occupied site was a site used by bumble bees to forage at some time during our survey period (as opposed to a nesting site; see Iles et al., 2019). To address model assumptions of closure to changes in occupancy, we constrained surveys to times and weather conditions when we expected bumble bees to be actively foraging. ...
... Nest building relates to several dimensions of evolutionary and behavioural ecology, such as habitat choice, reproductive effort, sexual selection or offspring survival. Nests can also be used to assess species presence or estimate populations in case of low breeder's detectability (Iles et al., 2019). When each individual builds one nest, and when each nest is built by a single individual, population assessment is straightforward. ...
Nests are widespread in the animal world and aim to protect the young from predation and adverse environmental conditions while being a privileged place to assess sexual selection. These nests, modifications of the habitat in which they are built, influence the environmental conditions and likely affect the communities and
ecological processes. Among the nesting species, the sea lamprey (Petromyzon marinus L.) is an anadromous, semelparous migratory fish, whose nests consist of a mound of coarse elements downstream a pit with a fine substrate. The thesis firstly describes the reproductive behaviour of the sea lamprey by studying the link between the nests and the individuals that built them. A Capture-Mark-Recapture protocol showed that males and females visited up to 10 and 7 nests respectively, and that nests could be built by either pairs or groups of up to 5 individuals, resulting in a clearly polygynandrous mating system. Data obtained during this individual monitoring was used to set up a model providing a population size estimate via a simple nest count, a model that can be easily adapted to other populations and used via an online application. Intrasexual competition and cooperative nest building, as well as the existence of potential alternative reproductive tactics, were monitored at the scale of a nest and of an entire spawning site. Video monitoring within nests showed equal individual contributions to both nest building and mating, although aggressions perpetrated by some males suggested a hierarchy. Experimental injection of eggs into recently built nests indicated that the interaction between variables related to habitat choice (current velocity) and habitat modification (slope between the lower and upper points in the nest) affected egg retention in the nest, a major aspect of egg survival. Measurements of the maintenance of river lamprey (Lampetra fluviatilis L.) eggs in a controlled environment showed a significant role of substrate size. Finally, the link between the nest and its ecosystem was described through the study of the macroinvertebrate communities occupying the different zones and several ecosystem processes. The habitat heterogeneity created by sea lamprey generated biological heterogeneity, with an increased invertebrate diversity in the nest compared to control sites. However, nutrient retention, chlorophyll accretion and litter degradation were not affected. The general objective of this thesis is thus a better understanding of a species whose ecology and place in the ecosystem remain poorly understood, although threatened in its native range while being invasive where introduced, through the use of a characteristic structure of its life cycle: the nest.
... Once we recognize that bees can be identified in the field, we can use old-school methods to study them throughout their life cycles. Methods like mark-recapture, nest excavations, and trap nests, which were commonplace in 20 th century natural history studies of bees (Linsley et al. 1952), are still some of the best suited tools for studying wild bee populations (Iles et al. 2019;Williams et al. 2019;Wong & Forrest 2021) (Fig. 1). ...
In recent years, ecologists have focused on describing patterns of change in wild bee communities, but we know little about the population-level mechanisms driving those changes. We believe this emphasis on community-level patterns stems from two misconceptions: the perceptions that population-level studies are too conceptually narrow to provide rigorous inference, and that studying bees throughout their life cycles is prohibitively challenging without pinned specimens. Here, we combat these ideas. First, when population-level studies are couched in ecological theory, they can also have a broad scope of inference. And second, studies of wild bees throughout their life cycles are possible because dozens of species can be identified to species in the field. More generally, we emphasize the need to link data-rich pattern-oriented approaches in ecology with an understanding of the basic biology and mechanisms that generate those patterns.
... By the time we began collecting data, we expected high turnover of foraging workers, as their life span in the wild is short (< 20 days in a field study of an ecologically similar species, B. vosnesenskii . During this 3-week acclimation period, we located four wild B. impatiens colonies during each year of the study by freely searching the study site for workers entering or exiting colony entrances (Iles et al. 2019). Although commercial colonies were located at the edge of our study meadow (see Appendix 1), the field we worked in was quite small, less than half a hectare. ...
Bumble bees (Bombus spp.) have been commercially propagated for over three decades. As the environmental conditions experienced by commercial bumble bees differ greatly from those experienced by wild bumble bees, commercial rearing of bumble bees may cause phenotypic changes. Here, we compare the foraging behavior and size of worker bumble bees (Bombus impatiens) from commercial and wild colonies. For this experiment, we measured worker body size, recorded if the workers returned with pollen, and examined the contents of pollen loads via microscopy. We found that, while commercial and wild bumble bees foraged on similar communities of flowers, wild bumble bees returned to colonies with purer pollen baskets (higher proportion of the most common species) and were more likely to return to the colony with pollen than their commercial counterparts. Commercial bumble bees were also smaller than wild bees. Our work highlights differences between commercial and wild bumble bees, in addition to raising important unanswered questions about the mechanism and drivers of these differences.
... At a set of study sites near Ipswich, Massachusetts, USA, we identified nesting habitat use by locating Bombus nest sites in three different land cover types. For the most commonly sighted species, B. impatiens, we estimated nest densities using mark-resight methods (Iles et al. 2019) to account for imperfect detection of nests and the possibility of habitat-specific differences in detection probability. We also monitored the reproductive output of B. impatiens nests we located in different land cover types by collecting gynes (female social insects with the potential to become queens) outside of nest entrances, as a way to assess habitat quality from a demographic perspective. ...
... Once a potential nest site was located, we confirmed the presence of a nest by waiting for at least four workers to exit or enter (Rao and Skyrm 2013). The first time a nest was located, the nest entrance was marked with an inconspicuous, numbered metal plant tag, and a single worker from each nest was collected to identify the colony to species (Iles et al. 2019). During subsequent searches, we recorded whether the nest was re-sighted to generate a capture history for each nest. ...
... Re-sighting a nest required the nest to be located using the same protocol, rather than by sighting the nest by memory or by locating an ID tag. Nest searches were carried out when B. impatiens colonies were large and when worker traffic at nest entrances was noticeable: from July 13th to August 15th in 2018 and July 12th to August 14th in 2019 (Iles et al. 2019). All surveys were conducted between 8:00 a.m. and 6:00 p.m. when the weather was clear. ...
Understanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at‐risk species. Although it is well known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources. In this study, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output for Bombus impatiens, the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also assessed nesting habitat associations for all Bombus nests located during surveys to tease apart species‐specific patterns of habitat use. We found that B. impatiens nested under the ground in two natural land cover types, forests, and meadows, but found no B. impatiens nests in hay fields. Though B. impatiens nested at similar densities in both meadows and forests, colonies in forests had much higher reproductive output. In contrast, B. griseocollis tended to nest on the surface of the ground and was almost always found in meadows. B. perplexis was the only species to nest in all three habitat types, including hay fields. For some bumble bee species in this system, meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However, B. impatiens might benefit from heterogeneous landscapes with forests and meadows. Results for B. impatiens emphasize the longstanding notion that habitat use is not always positively correlated with habitat quality (as measured by reproductive output). Our results also show that habitat selection by bumble bees at one spatial scale may be influenced by resources at other scales. Finally, we demonstrate the feasibility of direct nest searches for understanding bumble bee distribution and ecology.
... Nest building relates to several dimensions of evolutionary and behavioural ecology, such as habitat choice, reproductive effort, sexual selection or offspring survival. Nests can also be used to assess species presence or estimate populations in case of low breeder's detectability (Iles et al., 2019). When each individual builds one nest, and when each nest is built by a single individual, population assessment is straightforward. ...
Nest building relates to reproductive effort, sexual selection, intersexual conflict and cooperation and may be linked to individual phenotype and interindividual interactions. In particular, larger individuals having more energy reserves are expected to build more, larger nests, without having to trade intrasexual competition for cooperative nest building. Capture–mark–recapture and nest survey of sea lamprey (Petromyzon marinus L. 1758) were combined to assess the relationship between individuals and nesting activity on a spawning ground, throughout a breeding season, during which 202 nests were observed and 114 individuals were captured. On average, males and females stayed 8.33 ± 1.02 and 3.57 ± 1.04 days on the spawning ground, visited 2.26 ± 1.72 and 1.67 ± 1.17 nests and encountered 2.33 ± 2.13 mates for males and 2.29 ± 1.32 mates for females, respectively, and the number of mates encountered increased with the number of nests visited. Body size had no effect on the duration of presence on spawning ground, number of nests visited, number of individuals per nest and sex ratio on nest or nest volume. Bigger nests were found at the end of the season and were not necessarily built by more individuals. This work brings insights on the mating system and cooperative nest building in sea lamprey and may inform managers who want to estimate sea lamprey populations via nest surveys.
... Bombus nests are much harder to find than foraging worker bees, they are not harder to find than some other taxa that have been widely studied with these basic demographic tools, e.g., groundnesting birds. At a set of landscapes near Ipswich, Massachusetts, USA, we identified nesting habitat use by locating Bombus nest sites across three land cover types, using mark-resight methods (Iles et al. 2019) to account for imperfect detection of nests and the possibility of habitat-specific differences in detection probability. After locating nests, we evaluated nesting habitat quality by estimating the reproductive output of colonies of the most common species, B. impatiens in different land cover types. ...
... Once a potential nest site was located, we confirmed the presence of a nest by waiting for at least 4 workers to exit or enter (Rao and Skyrm 2013). The first time a nest was located, the nest entrance was marked with an inconspicuous, numbered metal plant tag, and a single worker from each nest was collected to identify the colony to species (Iles et al. 2019). During subsequent searches, we recorded if the nest was re-sighted to generate a capture history for each nest. ...
... During subsequent searches, we recorded if the nest was re-sighted to generate a capture history for each nest. Nest searches were carried out when B. impatiens colonies were large and when worker traffic at nest entrances was noticeable: from July 13 th to August 15 th in 2018 and July 12 th to August 14 th in 2019 (Iles et al. 2019). All surveys were conducted between 8:00 AM and 6:00 PM when the weather was clear. ...
Understanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at-risk species. Although it is well-known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources.
Here, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output for Bombus impatiens , the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also recorded nest site characteristics, e.g., the position of each nest site, for all Bombus nests located during surveys to tease apart species-specific patterns of habitat use.
We found that B. impatiens nests exclusively underground in two natural land cover types, forests and meadows, but not in hay fields. B. impatiens nested at similar densities in both in meadows and forests, but colonies in forests had much higher reproductive output.
In contrast to B. impatiens, B. griseocollis frequently nested on the surface of the ground and was almost always found in meadows. B. bimaculatis nests were primarily below ground in meadows. B. perplexis nested below ground in all three habitat types, including hay fields.
For some bumble bee species in this system, e.g., B. griseocollis and B. bimaculatis , meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However, B. impatiens might benefit from heterogeneous landscapes with forests and meadows. Further research would be needed to evaluate whether hay fields are high-quality nesting sites for the one species that used them, B. perplexis .
Synthesis and applications . In the past, Bombus nesting studies have been perceived as prohibitively labor-intensive. This example shows that it is possible to directly measure nesting habitat use and quality for bumble bee species. Applying these methods to more areas, especially areas where at-risk Bombus spp. are abundant, is an important next step for identifying bumble bee habitat needs throughout their life cycles.
... However, these methods are limited to species that maintain persistent nesting aggregations for long periods, whereas other species move nesting areas in subsequent years despite nesting in huge aggregations (e.g., a population of 423,000 female Centris caesalpiniae Cockerell; Rozen and Buchmann 1990). Nest counting and detection methods have also been used to quantify the number of bumble bee colonies in the landscape (Harder 1986, Lye et al. 2012, Iles et al. 2019) and these methods could be expanded to monitor populations over time. ...
Effective monitoring is necessary to provide robust detection of bee declines. In the United States and worldwide, bowl traps have been increasingly used to monitor native bees and purportedly detect declines. However, bowl traps have a suite of flaws that make them poorly equipped to monitor bees. We outline the drawbacks of bowl traps, as well as other passive sampling methods. We emphasize that current methods do not monitor changes in bee abundance. We then propose future approaches to improve bee monitoring efforts, which include improving our understanding of the efficacy and drawbacks of current methods, novel molecular methods, nest censusing, mark-recapture, sampling of focal plant taxa, and detection of range contractions. Overall, we hope to highlight deficiencies of the current state of bee monitoring, with an aim to stimulate research into the efficacy of existing methods and promote novel methods that provide meaningful data that can detect declines without squandering limited resources.
While interactions in nature are inherently local, ecological models often assume homogeneity across space, allowing for generalization across systems and greater mathematical tractability. Density-dependent disease models are a prominent example that assumes homogeneous interactions, leading to the prediction that disease transmission will scale linearly with population density. In this study, we examined how larval butterfly contact rates relate to population density in the Baltimore checkerspot ( Euphydryas phaeton ). Our study was partly inspired by a viral disease that is transmitted horizontally among Baltimore checkerspot larvae. First, we used multi-year larvae location data across six Baltimore checkerspot populations in the eastern U.S. to test whether larval nests are spatially clustered. We then integrated these spatial data with larval movement data. We used a Correlated Random Walk (CRW) model to investigate whether heterogeneity in spatially local interactions alter the assumed linear relationship between population density and contact. We found that all populations exhibited significant spatial clustering in their habitat use. Larval movement rates were influenced by encounters with host plants, and under many movement scenarios, the scale of predicted larval movement was not sufficient to allow for the “homogeneous mixing” assumed in density dependent disease models. Therefore, relationships between population density and larval contact rates were typically non-linear. We also found that observed use of available habitat patches led to significantly greater contact rates than would occur if habitat use were spatially random. These findings strongly suggest that incorporating spatial variation in larval interactions is critical to modeling disease outcomes in this system.
Movement of foraging animals can be used as an indirect index of habitat quality because movement patterns are expected to shift in association with resources resulting in increased time spent in high‐quality habitat. Here, we observed movement of bumblebee ( Bombus impatiens ) queens as an indirect metric of nesting habitat quality.
At a farm in Massachusetts, we recorded flight paths by visual observation of nest‐searching B. impatiens queens in three land cover types (hay fields, meadows and forests). According to previous research at this field site, these land cover types represent both high‐quality (meadows, forests) and low‐quality habitat (hay fields) for nesting bumblebees. Using flight path data, we estimated diffusion coefficients of nest‐searching queens (i.e., the rate at which queens explore habitat during nest‐searching), as an integrative measure of movement.
We found that nest‐searching queens explored meadows and forests more slowly than hay fields; we calculated diffusion coefficients of 0.198, 0.272, and 0.762 m ² s ⁻¹ for bees searching for nests in meadows, forests, and hay fields, respectively. In hay fields, nest‐searching queens had smaller step lengths and straighter flightpaths than in other land cover types.
Nesting ecology of bumblebees is a key knowledge gap. We showed that nest‐searching queens search more thoroughly in areas associated with previously reported high nest densities. Therefore, our research suggests that behaviour of nest‐searching queens can also be a proxy for nesting habitat quality. Extending these methods to other Bombus species in other landscapes would be a valuable direction for future research.
