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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
Source publication
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
... Methods for studying field-identifiable bees throughout their life cycles have their roots in the 20th century (Linsley, MacSwain, & Smith, 1952;Michener et al., 1955). These techniques, including locating and excavating nests, monitoring emergence, and mark-recapture are still some of the best suited tools for studying wild bee populations today (Iles et al., 2019;Williams et al., 2019;Wong & Forrest, 2021) (Figure 1). To facilitate the use of these methods in the 21st century, we have summarized classic field methods for studying bee populations in a step-by-step guide (Appendix S2). ...
In recent years, motivated by widespread declines in wild bees, ecologists have prioritized learning about patterns of wild bee communities across the landscape at the expense of learning about the population‐level mechanisms driving those patterns. In this essay, we seek to revitalize the tradition of studying wild bee populations in a way that both contributes key knowledge for bee conservation and builds a strong conceptual understanding of the processes underpinning bee populations. We address two widespread concerns about investing in population‐level research. First, that population‐level studies are too conceptually narrow to provide broad inference. If population‐level studies are couched in general ecological theory, then findings from a single species can be generalized to many. We highlight how wild bees would make excellent candidates for exploring five areas of general ideas in population ecology, including nutritional ecology, drivers of vital rates, phenology and voltinism, habitat selection, and movement. Second, we address the concern that methods for studying bees at the population level are too difficult to implement. Methods for conducting population‐level studies of bees—specifically, identifying living bees in the field and studying individuals throughout their life cycles—are feasible to implement at the scales appropriate for answering population‐level questions, for example, a few species at a few sites. To facilitate adoption of these ideas, we developed an online field guide (www.watchingbees.com) and a detailed methods manual. More generally, we emphasize the value of linking data‐rich pattern‐oriented approaches in ecology with an understanding of the basic biology and mechanisms that generate those patterns.
... Each site was visited multiple times during the larval prediapause period in late summer, and nests were surveyed using a sight-resight protocol similar to that detailed in Iles et al. [44], as described by Brown et al. [11]. The surveyor slowly walked over the entirety of the site, and when nests of larvae were found they were recorded and geolocated. ...
Background
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 of models that assume homogeneous interactions, leading to the prediction that disease transmission will scale linearly with population density. In this study, we examined how the scale of larval butterfly movement interacts with the resource landscape to influence the relationship between larval contact and population density in the Baltimore checkerspot (Euphydryas phaeton). Our study was inspired by the recent discovery of a viral pathogen that is transmitted horizontally among Baltimore checkerspot larvae.
Methods
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 in different resource contexts to investigate whether heterogeneity in spatially local interactions alters the assumed linear relationship between larval nest density and contact. We used Correlated Random Walk (CRW) models and field observations of larval movement behavior to construct Probability Distribution Functions (PDFs) of larval dispersal, and calculated the overlap in these PDFs to estimate conspecific contact within each population.
Results
We found that all populations exhibited significant spatial clustering in their habitat use. Subsequent larval movement rates were influenced by encounters with host plants and larval age, 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 were typically non-linear. We also found that observed use of available habitat patches led to significantly greater contact than would occur if habitat use were spatially random.
Conclusions
These findings strongly suggest that incorporating larval movement and spatial variation in larval interactions is critical to modeling disease outcomes in E. phaeton. Epidemiological models that assume a linear relationship between population density and larval contact have the potential to underestimate transmission rates, especially in small populations that are already vulnerable to extinction.
... This study adds another piece to the growing body of evidence that also sessile organisms are far from being perfectly detected (Kéry & Gregg, 2003;Cáceres et al., 2008;Garrard et al., 2008Garrard et al., , 2013Chen et al., 2009Chen et al., , 2013Vittoz et al., 2010;Casanovas et al., 2014;Berberich et al., 2016;Morrison, 2016;Vondrák et al., 2016;Brown et al., 2017;Dennett et al., 2018;Dennett & Nielsen, 2019;Iles et al., 2019;Middleton & Vining, 2022;Perret et al., 2023). Yet, detection probability is not commonly accounted for in analyses of occurrence or abundance data from plants, lichens and other sessile organisms. ...
Question
What are the extent and the possible causes of imperfect detection in lichens? Because lichens are sessile and lack seasonality, they should be easier to survey than animals that can move or plants and fungi with seasonal morphology, and one could therefore expect relatively high detection probabilities.
Location
826 standardised sampling plots across Switzerland.
Methods
Using repeated detection/non‐detection data from a national lichen survey conducted by professional lichenologists, we estimated the mean and variation in detectability for 373 tree‐living species with a multi‐species occupancy model. We also quantified the effect of species conspicuousness, identifiability and observer experience on detection probability.
Results
The average detection probability for a single survey was unexpectedly low with an average of 0.49 (range across species: 0.25–0.74). Conspicuous species showed higher average detectability (0.56) than inconspicuous species (0.41), and identifiability as well as previous experience with a species substantially increased the probability of a person detecting it. Accounting for experience, the mean detection probabilities of observers ranged from 0.32 to 0.69.
Conclusions
Our study confirms that detection probability per survey is often far below 1 also in sessile organisms, even when a standardised survey is conducted by experts. When species are seasonal (plants, fungi, etc.), survey areas are larger, or field personnel are less experienced, as is the case for many surveys and monitoring programs, detectabilities are likely to be substantially lower. We therefore argue that imperfect detection should systematically be considered in the survey design and data analysis also for sessile organisms.
... Floral abundance is associated with higher attractiveness to pollinators and thus higher foraging activity (Bartomeus et al., 2013), but other factors can influence pollinator visitation such as predation risk (Jones & Dornhaus, 2011) and competition with other wild pollinators (Ropars et al., 2019). The findings of potential species-specific patterns in detectability highlight the necessity of accounting for imperfect detection to generate accurate and unbiased population estimates in bumble bees and in other pollinator groups (Iles et al., 2019;Kéry & Schmidt, 2008;MacKenzie et al., 2002;Mata et al., 2014) F I G U R E 6 Estimated difference of floral abundance effects in predominantly urban sites relative to predominantly agricultural sites (±85% CI). Positive values represent increase in occupancy in urban sites relative to agricultural sites and negative values represent decrease in occupancy in urban sites relative to agricultural sites. ...
Loss of natural habitat due to increases in agricultural extent raises the question of whether human‐dominated landscape types can support biodiversity, particularly for declining insect pollinators. Compared to more rural agricultural landscapes, urban areas may confer benefits for bumble bee populations by providing stable and diverse floral resources. However, disentangling the effects of local‐ and landscape‐scale characteristics on bumble bee populations in human‐modified landscapes is challenging.
Here, we assessed bumble bee occupancy using a repeated transect sampling design conducted during the summers of 2019 and 2020 within the metropolitan area of Madison, WI, and the surrounding agricultural landscape. We fit hierarchical occupancy models to estimate the detection ( p ) and occupancy () probabilities relative to local habitat quality (floral abundance and floral richness) and landscape (agricultural‐urban gradient) features for eight bumble bee species. We hypothesised that bumble bees were more likely to occupy urban areas, serving as refugia, relative to agricultural sites.
We found that the detection probability of all bumble bee species was seasonal and influenced by maximum floral abundance at survey sites, independent of the surrounding land cover type. After accounting for species‐specific detection probabilities, the effect of urbanisation on bee occupancy was weak, and no species were less likely to occupy urban than rural agricultural areas.
Our findings suggest that bumble bee occupancy is associated with a ‘honeypot effect’ where local resource availability, in the form of higher floral abundance, is most important in limiting the occupancy of bumble bees across urban and agricultural landscapes.
... 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.