GEOG 560, GIScience I: Introduction to Geographic Information Science, Fall 2024
Michael Baltzley

I am in the early stages of developing a project to examine the microhabitats and potential habitat overlap between the native Pacific sideband snail, Monadenia fidelis, and an introduced snail (Cornu aspersum) in Oregon. Below is an annotated bibliography for my background reading to date.
The references have been grouped into two categories: papers related to “Citizen Science” and papers related to “Snail Distribution and Physiology”. Each abbreviated citation can be expanded to show the full citation, my summary of the paper, and its relevance to my planned project.
Citizen Science
Backstrom, et al. 2024. Ecology and Evolution, 14(2), e10857
Backstrom, L. J., Callaghan, C. T., Leseberg, N. P., Sanderson, C., Fuller, R. A., & Watson, J. E. (2024). Assessing adequacy of citizen science datasets for biodiversity monitoring. Ecology and Evolution, 14(2), e10857. https://doi.org/10.1002/ece3.10857
Summary: The authors assessed the quality of data collected by citizen scientists using two different applications, eBird and Birdata. They examined (1) how complete the citizen data was on inventorying bird species and (2) whether there was a spatial bias in the data collection. The authors then modeled the two data quality metrics against 7 species traits to see if there were predictable patterns in the data collection. The species traits they chose included some that were population level (e.g., threat status, taxonomic uniqueness), some that were physical traits (e.g., body mass), and some that were environmental (e.g., human density). The authors found that species with larger ranges had less complete sampling and a stronger spatial bias. In other words, species with a large range are harder to sample. Additionally, species in areas more densely populated by humans had more complete sampling, but also had a stronger spatial bias. This last finding is consistent with other literature that finds that citizen science data is biased towards areas densely inhabited by humans.
Relevance: I’m interested in trying to map distributions of two snail species using citizen science data. The most important take-home points from Backstrom, et al., 2024 are that (1) data on some species is likely reliable, but data on species that are rare or have large or remote ranges are likely insufficient, and (2) assessment of data adequacy at the species-level is necessary. One of the two species (Monadenia fidelis) that I am interested in is native to Oregon, and can be found throughout the Coastal Range; the findings of this paper indicate that M. fidelis is likely under-surveyed. The other species, Cornu aspersum, is invasive and has generally been reported in the Willamette Valley and coastal Oregon. It is very possible that C. aspersum is found in the Coastal Range, but is under-surveyed. I’ll need to consider how to address this concern in any data analyses.
Bowler, et al. 2022. Scientific Reports, 12(1), 11069.
Bowler, D. E., Bhandari, N., Repke, L., Beuthner, C., Callaghan, C. T., Eichenberg, D., Henle, K., Klenke, R., Richter, A., Jansen, F., Bruelheide, H., & Bonn, A. (2022). Decision-making of citizen scientists when recording species observations. Scientific Reports, 12(1), 11069. https://doi.org/10.1038/s41598-022-15218-2
Summary: The authors surveyed about 900 people about their decision making while collecting data for citizen-science data collection. General findings were that most people were motivated by improving species knowledge and supporting conservation, and that many people participate in active species surveys and also report species opportunistically. When reporting opportunistically, people are more likely to report rare species only. People are also less likely to report a species that they have seen before in the same location. The authors also found that most people look for species in natural or semi-natural habitats, such as wetlands, meadows, and forests, and look less often in urban and agricultural areas.
Relevance: C. aspersum is not a rare species, so might be underreported. However, it is a fairly well-known introduced species, so it is also possible that people might be motivated to report observations. Since people are less likely to report species that they have seen before in a given location, it would be challenging to use iNaturalist data to make conclusions about whether the native snail, M. fidelis, no longer lives in a particular area. In contrast, the finding that people report animals less often in urban and agricultural areas suggests that the prevalence of M. fidelis in the Willamette Valley could be greater than it appears to be in the iNaturalist data.
Di Cecco, et al. 2021. BioScience, 71(11), 1179-1188.
Di Cecco, G. J., Barve, V., Belitz, M. W., Stucky, B. J., Guralnick, R. P., & Hurlbert, A. H. (2021). Observing the observers: How participants contribute data to iNaturalist and implications for biodiversity science. BioScience, 71(11), 1179-1188. https://doi.org/10.1093/biosci/biab093
Summary: The authors examined all iNaturalist observations from 2008 through 2019 (31 million observations!!) to examine spatial and temporal biases in the collected data, and to examine taxonomic biases and the taxonomic specialization of observers. The authors found that developed areas were highly over-sampled and deciduous forest areas were slightly over-sampled. In comparison, scrublands, grasslands, and areas of cultivated crops were significantly under-sampled.
The authors grouped users based on their proportion of taxonomic observations. The largest two groups consisted of 80% of observers. These groups made their majority of observations on plants and insects, which is consistent with the findings of Dimson and Gillespie, 2023 (see below). The authors also calculated the proportion of species within different taxonomic classes of organisms that had been observed. They found that as the number of species within a class increased, the proportion of species that were observed decreased. While insects are the most observed class of animals, the proportion of insects that have been observed is much lower than the proportion of birds, reptiles, mammals and amphibians. Gastropods, similar to insects, have a low proportion of observed species.
The authors also found that most observers made only one observation per species, indicating a bias for novel observations.
Relevance: Because C. aspersum lives in highly developed areas and is likely to be observed there by citizen scientists interested in gastropods, they may be less likely to be reported when they are subsequently observed in other areas. The authors suggest that, based on the behavioral patterns of observers, focusing on data collected by more active users should lead to a reduction in spatial bias. They also suggest normalizing observations by the total observations to correct for user behavior if the goal is to monitor species distribution changes.
The authors make a strong case for not using sampling patterns to predict temporal shifts in animal distributions because observers are more active on weekends. Because the day of the week and the date shift by one day every year, and two days on leap years, examining when observations are made over a short time span will create the perception of a temporal shift, when in reality it is an observer behavior shift. For my research interests, this is particularly relevant to consider if C. aspersum and M. fidelis are active at slightly different times of the year.
Díaz-Calafat, et al. 2024. PLoS one, 19(7), e0305757.
Díaz-Calafat, J., Jaume-Ramis, S., Soacha, K., Álvarez, A., & Piera, J. (2024). Revealing biases in insect observations: A comparative analysis between academic and citizen science data. PLoS One, 19(7), e0305757. https://doi.org/10.1371/journal.pone.0305757
Summary: The authors compared the biases in sampling data in a citizen science database compared to academic data. Citizen scientists were biased towards observations of Lepidopterans (butterflies and moths). However, compared to academic data, citizen science data had better spatial coverage. Citizen science data was more biased towards cities and roads, while academic data was biased toward protected natural areas and cities. Both types of data have biases towards certain environmental parameters, but because the environmental parameters were analyzed using a principal component analysis, the data was collapsed into two principal components and specific environmental parameters weren’t identified.
Relevance: This study provides a good argument for using citizen science data to monitor species distribution. Citizen science data has biases, which researchers need to be aware of and to acknowledge…but so does academic data.
Dimson, et al. 2023. Diversity and Distributions, 29(9), 1141-1156
Dimson, M., Berio Fortini, L., Tingley, M. W., & Gillespie, T. W. (2023). Citizen science can complement professional invasive plant surveys and improve estimates of suitable habitat. Diversity and Distributions, 29(9), 1141-1156. https://doi.org/10.1111/ddi.13749
Summary: Recognizing that both structured field observations by professionals and unstructured field observations by non-professionals have strengths and weaknesses, the authors investigated how data on the occurrence of invasive plant species differed between professional observations and citizen observations in iNaturalist. The authors focused on three types of environmental biases: (1) proximity to roads and trails, (2) whether the sampling location was in or near an area of “conservation interest”, and (3) how heavily disturbed the sampling location was. Then then examined how well the different data sets performed in creating habitat suitability models.
The authors found that iNaturalist data was biased against endemic species and towards invasive species. However, the bias against endemic species is likely due to the bias for sampling in areas that are close to roads and trails and areas that are heavily disturbed. The iNaturalist data and the professional data both generated good habitat suitability models, but models that combined the two data sets produced the most comprehensive habitat suitability estimate.
Relevance: The authors chose to use Hawaii as their experimental site because of the extensive availability of professional data on their organisms of interest. I won’t have a similar data set available for C. apsersum and M. fidelis, but the authors found that even the iNaturalist data alone created reasonable habitat suitability models. I didn’t dig very deep into their statistical analysis, but I found it surprising that every one of the comparisons they presented (over 400) was statistically significant.
Dimson & Gillespie. 2023. Applied Geography, 153, 102916.
Dimson, M., & Gillespie, T. W. (2023). Who, where, when: Observer behavior influences spatial and temporal patterns of iNaturalist participation. Applied Geography, 153, 102916. https://doi.org/10.1016/j.apgeog.2023.102916
Summary: The authors studied participation in iNaturalist from 2008 through 2021 in the Hawaiian islands, with a particular interest in how the COVID pandemic affected the collection of data. The studied focused on how observer behavior affected the quality of observations and the spatial pattens of observations, as well as the patterns of observations over time. The authors were interested in the differences in observer behavior for residents compared to visitors to Hawaii, and classified observers as residents or visitors based on the proportion of their iNaturalist observations that were made in Hawaii.
The authors grouped observers into 3 activity levels—enthusiastic, moderate, and short-term. Hawaii residents were more likely to be moderate or short-term observers of Hawaiian wildlife, while visitors were more likely to be enthusiastic or moderate observers. Most observations were made in developed areas, and were within 150 m of a road or a trail. The number of observers and the number of observations increased steadily from 2008 to 2019. During 2020, the number of observers and observations decreased for visitors, but showed little to no change for residents.
Different taxonomic categories of organisms were reported at different rates by observers. Plants and algae were the most commonly reported category, followed (in descending order) by invertebrates, birds, reptiles, fish and amphibians. I’m not sure this finding says much about observer behavior—it likely says as much about how often organisms in those various taxonomic categories are encountered.
Relevance: Regarding the activity level of residents compared to visitors, these findings are consistent what the findings of Bowler et al, 2022 (see above). Bowler et al, 2022, found that people are more likely to report unique observations; if someone is a resident of Hawaii, they are less likely to perceive the local wildlife as unique. While I found the paper interesting, I didn’t find anything particularly relevant to my proposed study of snail populations in western Oregon. It is a good reminder that most observations will be made near roads or trails, and the iNaturalist observations are a very different type of “sampling” than a planned population survey.
Erickson, et al. 2023. Ecology and Evolution, 13(12), e10766.
Erickson, E., Jason, C., Machiorlete, H., de la Espriella, L., Crone, E. E., & Schultz, C. B. (2023). Using community science to map western monarch butterflies (Danaus plexippus) in spring. Ecology and Evolution, 13(12), e10766. https://doi.org/10.1002/ece3.10766
Summary: Even though monarch butterflies have been relatively well-studied, the extent of their spring breeding habitat is unknown because of the relatively small population size in the spring and the potentially large area that could be breeding habitat. The authors developed a citizen science program with the goal of assessing monarch populations and habitats in late Winter and early Spring. The authors used previous iNaturalist records, but also recruited participants through social media platforms, and asked them to submit monarch butterfly photos taken during the target time period. The authors used submitted pictures to identify habitat, but also to age the butterflies based on the extent of wing wear.
The amount of data on monarch butterflies in the study area that was available on iNaturalist increased dramatically after the authors began their citizen outreach program. The data collected supports the hypothesis that monarch spring breeding habitat in California ranges as far inland as the Sierra Nevada mountains. A practical implication of their study is that efforts to create monarch-friendly habitat should include the planting of early season milkweed throughout the Central Valley.
Relevance: While I formatted my annotated bibliography by theme (“Citizen Science” and “Snail Distribution and Physiology”), and then alphabetically within theme, I didn’t read and summarize the references in that order. This paper, while interesting, didn’t add much to my understanding of using iNaturalist as a data source for examining population distributions. The authors use of social media to try to increase iNaturalist submissions could be a useful tool to increase submitted observations of snails.
Hantak, et al. 2022. Biology Letters, 18(12), 20220403.
Hantak, M. M., Guralnick, R. P., Cameron, A. C., Griffing, A. H., Harrington, S. M., Weinell, J. L., & Paluh, D. J. (2022). Colour scales with climate in North American ratsnakes: a test of the thermal melanism hypothesis using community science images. Biology Letters, 18(12), 20220403. https://doi.org/10.1098/rsbl.2022.0403
Summary: According to the thermal melanin hypothesis, when there is color variation within a species, darker animals will be found in colder regions because the dark pigmentation aids in absorption of solar radiation. The authors tested this hypothesis in 3 species of rattlesnakes by examining color patterns in iNaturalist images. The authors found that in all species of snake, black coloration was correlated with annual mean temperature. Annual precipitation and elevation were also predictors of coloration for some species, but not all.
Relevance: This study is superficially similar to my proposed study in that the authors do not need data on abundance of snakes, just photographic evidence of presence or absence (and in their case, color). While I found their study interesting, it’s not directly relevant to my proposed study; however, it is great as proof-of-concept and will be a useful resource for figuring out how and where to get habitat data.
Harman, et al. 2024. Diversity, 16(9), 515.
Harman, A. J., Eori, M. M., & Hoback, W. W. (2024). A comparison of butterfly diversity results between iNaturalist and expert surveys in eastern Oklahoma. Diversity, 16(9), 515. https://doi.org/10.3390/d16090515
Summary: The authors investigated how citizen science data on iNaturalist compared to systematic surveys performed by experts. The experts identified about three-fold more butterflies than were observed in iNaturalist, but both surveys identified about the same number of species (50-55), and each had about 10 unique species. The authors did not find any significant differences between the sampling performed by citizen scientists and the authors.
The authors stated that expert surveys showed a higher Shannon Diversity index, but they incorrectly calculated averages for the Shannon Diversity index across seasons and sampling locations because they calculated 0 when no species were reported by citizen scientists. This method of calculating averages would be like saying students at Oregon State are taller than students at the University of Oregon because OSU students have an average height of 5’ 6”, and students at U of O had an average height of 0’ 0” because no one measured their height. The authors concluded that iNaturalist data needs to be understood in context and does not replicate planned population surveys, but while they pointed out some strengths of iNaturalist, they interestingly did not conclude that planned surveys do not replicate iNaturalist surveys.
Relevance: Citizen science surveys are not the same as transect surveys, but this is not surprising. Every sampling technique has strengths and weaknesses. For identifying presence or absence of butterfly species, iNaturalist performed as well as the transect surveys. For my planned study, the data in this paper supports the argument that iNaturalist should be sufficient for establishing the presence or absence of C. aspersum and M. fidelis.
Neo. 2024. Journal of Molluscan Studies, 90(4), eyae038.
Neo, M. L. (2024). Guardians of the clams: a decadal monitoring effort of endangered giant clams by citizen scientists. Journal of Molluscan Studies, 90(4), eyae038. https://doi.org/10.1093/mollus/eyae038
Summary: The author used photos posted from 2011 to 2020 by citizen scientists to a public blog to estimate the presence and density of giant clams. The author stated that by using mantle patterns and site information, it was possible to avoid double-counting of individuals and to identify new sightings and repeat sightings of clams from year to year. Only two of five giant clam species were sighted during the study period, and the population density of the two species that were sighted was very low. Few juveniles were reported, which could suggest a low recruitment rate…or could be due to the fact that juveniles are harder to spot than adults.
Relevance: This study made good use of citizen science data but isn’t particularly relevant to my project—giant clams are relatively unique in that they are individually identifiable, long-lived and non-motile. My snails of interest are not easily individually identifiable, are short-lived, and are motile (ableit very slow).
Puchałka, et al. 2022. Agricultural and Forest Meteorology, 325, 109133.
Puchałka, R., Klisz, M., Koniakin, S., Czortek, P., Dylewski, Ł., Paź-Dyderska, S., Vítková, M., Sádlo, J., Rašomavičius, V., Čarni, A., De Sanctis, M., & Dyderski, M. K. (2022). Citizen science helps predictions of climate change impact on flowering phenology: A study on Anemone nemorosa. Agricultural and Forest Meteorology, 325, 109133. https://doi.org/10.1016/j.agrformet.2022.109133
Summary: The authors used data from several different databases, including iNaturalist, to determine the factors that drive both the onset and offset of flowering in Anemone nemorosa. A. nemorosa is widespread across Europe and is an important spring food source for many insects. They found that flowering onset and offset were both negatively correlated with mean annual temperature and annual precipitation (i.e., higher temperatures and more precipitation were correlated with earlier flowering onset and offset).
The authors also used projections of future climate to predict changes in onset and offset of flowering in the coming decades. The results suggest, not surprisingly, that flowering onset and offset can be expected to occur earlier in 2041-2080.
Relevance: While I’m interested in snails rather than flowers, this study is similar to my project idea in that they used a flower that is easily identifiable from iNaturalist photos, and both of the snails that I am interested in are easily identifiable from photos. Part of my original idea was to predict how the distribution of snails might change as climate changes. Although, I already have largely dismissed that idea because of the slow dispersal rates of snails (see Bergey, 2019, below), this study suggests that I might be able to use iNaturalist data to determine if snails are active for longer portions of the year as temperatures increase.
Willighagen, L. G., & Jongejans, E. 2024. Insect Conservation and Diversity, 17, 632-641.
Willighagen, L. G., & Jongejans, E. (2024). Mapping wing morphs of Tetrix subulata using citizen science data: Flightless groundhoppers are more prevalent in grasslands near water. Insect Conservation and Diversity, 17, 632-641. https://doi.org/10.1111/icad.12730
Summary: The authors used data from the Global Biodiversity Information Facility to study the habitat distribution of long-winged and short-winged morphs of grasshoppers. Various insect species have multiple wing morphologies, but there doesn’t appear to be a common driver of morphology type because there are many trade-offs for each morphology. For example, long wings allow for increased mobility and more dispersal, but are more energy intensive which can impact survivability and reproduction. The authors examined a number of environmental variables for each observed specimen, including water body type, soil composition, temperature, and precipitation.
The authors found that the long-winged morphs were more common. Long-winged morphs outnumbered short-winged morphs about 4:1 overall, but only outnumbered short-winged morphs less than 2:1 in river areas, fens and hills. Proximity of water, which is considered an indicator of preferred habitat, appeared to increase the proportion of short-winged morphs.
Relevance: This paper is another great example of the ability to use citizen science data to examine species distribution and habitat preferences. As I get further into developing my project idea, it could be a good resource for methods. It also pushed me into thinking about other features that I might be able to examine using iNaturalist. For example, are there differences in shell color or shell shape in snails in different habitats?
Snail Distribution and Physiology
Ansart & Vernon. 2004. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 139(2), 205-211.
Ansart, A., & Vernon, P. (2004). Cold hardiness abilities vary with the size of the land snail Cornu aspersum. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 139(2), 205-211. https://doi.org/10.1016/j.cbpb.2004.09.003
Summary: Ansart and Vernon, 2004, examined the ability of C. aspersum to survive freezing temperatures relative to body size. The authors grouped snails based on whether they were juvenile or adult, and whether they were collected from a region that has an average temperature of 8°C in the winter, but can drop to -5°C at night, or from a region that has an average temperature of 6°C in the winter, but can drop to -10°C at night. The authors found that smaller snails tended to have a lower temperature at which water crystallized, suggesting that smaller snails had mechanisms to resist freezing. As body mass increases, water content increases, so it takes longer for internal water to begin freezing; in other words, smaller snails need to spend energy to actively prevent freezing because they are more susceptible to freezing. Larger snails survived longer at exposure to freezing temperatures (-5°C), but no snails survived longer than 16 hours of exposure to -5°C.
Relevance: C. aspersum is an invasive species in Oregon, particularly in the Willamette Valley and the Pacific Coast. C. aspersum has generally been introduced accidentally by recreational gardeners and the agriculture industry. Presumably, snails are more likely to be introduced in areas with higher densities of humans. The snails have not spread much into the Coastal Range or Cascade Range. The restriction of their distribution could be due to their physiological abilities, or due to an inability to disperse rapidly, or a combination of both factors. This study suggests that freezing tolerance might be a factor in the distribution of C. aspersum. For example, the average January low temperature (https://www.usclimatedata.com/climate/oregon/united-states/3207) in Salem, OR, and Newport, OR, are 2°C and 4°C, respectively, while the average January temperature in Sisters, OR is -5°C.
Ansart, et al. 2014. Evolutionary Ecology, 28, 471-493.
Ansart, A., Guiller, A., Moine, O., Martin, M. C., & Madec, L. (2014). Is cold hardiness size-constrained? A comparative approach in land snails. Evolutionary Ecology, 28, 471-493. https://doi.org/10.1007/s10682-013-9680-9
Summary: Ansart et al., 2014, examined multiple factors that might predict survival in freezing temperatures in snails. There are two general strategies for surviving freezing temperatures, freezing avoidance and freezing tolerance. Freezing avoidance involves employment of supercooling strategies to prevent water from freezing because the formation of ice is lethal. Freezing tolerance involves allowing the slow freezing of tissues with protective measures that prevent the ice from causing damage. In snails, small species have been shown generally to be freezing avoidant, while large snails are generally freeze tolerant.
The authors examined 31 species of snails from 13 families. The 31 species represented a large range in body sizes and were collected from diverse geographical regions. They examined whether water content, natural distribution areas, maximum altitude, and various climatic indices could predict the temperature of crystallization. They found that water content was correlated with temperature of crystillisation, but environmental variables were not. The authors did not find differences due to phylogenetic relatedness, but argued that their study design does not rule out different cold tolerance strategies between species.
Relevance: The Pacific sideband snail, M. fidelis, is native to Oregon, and is similar in size to the invasive snail C. aspersum. If M. fidelis is more tolerant of cold temperatures than C. aspersum, this study suggests that C. aspersum could be geographically restricted to warmer areas and that climate change could result in C. aspersum expanding its range further into the Coastal Range and Cascade Range.
Bergey. 2019. Urban Ecosystems, 22(2), 325-334.
Bergey, E. A. (2019). Dispersal of a non-native land snail across a residential area is modified by yard management and movement barriers. Urban Ecosystems, 22(2), 325-334. https://doi.org/10.1007/s11252-018-0815-1
Summary: This study was an Investigation of how the invasive snail C. aspersum disperses after it is introduced. The author surveyed snail populations in a residential neighborhood 6 years after presumed introduction. The study included a survey of snail populations and of various yard features such as vegetation, supplemental watering, dog presence, and pesticide use. The author ran several different distribution models and compared the models to the observed distribution of snails. The greatest distance the author found snails from the site of introduction was 110 m, which represented a dispersal rate of about 18 m/yr. Several other studies with other species of snails were mentioned—one reported a dispersal rate of about 30 m/yr, and the other reported a rate of about 120 m/yr.
The observed density of snails was predicted by the number of contiguous yards with snails, yard watering, water features, and lower shade temperatures. The author concludes that it is unlikely that C. aspersum could establish populations outside urban areas because of associations with moderated temperatures in microhabitats (housing foundations, water features) and access to supplemental water. Importantly, the study supports the conclusion that roads are barriers to dispersal for C. aspersum.
Relevance: Any rapid expansion of C. aspersum in the Willamette Valley and coastal Oregon is more likely to be due to passive transport by humans, rather than spreading from the area of introduction. Using the dispersal rate reported in the paper of 18 m/yr, and estimating the linear distance from Dallas, OR, to the Pacific Ocean as approximately 56 km, it would take about 1500 years for a population of C. aspersum in Dallas to reach the mid-point of the Coastal Range between Dallas and Lincoln City, OR. However, the Willamette Valley is likelier to be a suitable habitat for snails than the study site of Norman, OK: the average January low temperature in Norman is -3°C, and the average July high temperature is 33°C, while the respective averages for Dallas, OR, are 2°C and 28°C. The more moderate temperatures in Dallas, OR, would mean that snails are (1) more likely active for a longer time each year, (2) are more likely to survive cold winter periods and hot, dry summer periods, and (3) are more likely to find suitable habitat that is not associated with urban areas. Nonetheless, even if C. aspersum is more likely to disperse naturally in the Willamette Valley than in central Oklahoma, a bigger concern than dispersal of C. aspersum might be its competition with M. fidalis in natural habitats that are near densely populated areas.
Brown & Durand. 2007. Habitat assessment for the Fraser Valley Conservancy Society, Abbotsford, BC.
Brown, D., & Durand, B. R. (2007). Habitat assessment of the Pacific Sideband (Monadenia fidelis) In the Lower Fraser Valley British Columbia. Fraser Valley Conservancy Society, Abbotsford, BC.
Summary: The authors surveyed the biotic and abiotic conditions where M. fidelis were found near Abbotsford, British Columbia. They measured biotic factors such as forest type, age, canopy cover, herb cover, etc., and abiotic factors such as slope and substrate. The authors found that snails were generally located in leaf litter in deciduous forests that had big leaf maple, red alder, vine maple, salmonberry, and sword ferns. The snails were more likely to be found in areas that had not undergone significant “disturbance” in 20 years, and were generally not found in lowland areas.
Relevance: The authors finding that M. fidelis prefers undisturbed areas aligns fairly well with the data on iNaturalist which generally shows M. fidelis in undeveloped Coastal and Cascade Range forests. The iNaturalist data on M. fidelis seems like it provides the opportunity to examine broader microhabitat preferences for M. fidelis. Many of the features that the authors examined—such as the types of plants found at each sample location—will not be available on a larger scale, but forest types, rainfall, elevation, slope, and substrate might be.
Oswald, et al. 2021. Conservation Genetics, 23, 299-311.
Oswald, J. A., Roth, B., Faske, T. M., Allen, J. M., Mestre, C., Rivers-Pankratz, D., Van Norman, K., & Guralnick, R. P. (2022). Population genomics of Monadenia (Gastropoda: Stylommatophora: Xanthonychidae) land snails reveals structuring but gene-flow across distinct species and morphotypes. Conservation Genetics, 23, 299-311. https://doi.org/10.1007/s10592-021-01410-w
Summary: There are 5 species in the genus Monadenia that are found in western North America, from northern California to British Columbia. M. fidelis is composed of 8 recognized subspecies. The authors used genetic data to determine the diversity of the various species and subspecies in California, Oregon and Washington. The authors found that the various populations of Monadenia demonstrated significant gene flow across taxanomic groups and little genetic distinctness. Additionally, the authors argue that the genetic data indicates that Monadenia in Oregon have large effective population sizes.
Relevance: Data in iNaturalist generally doesn’t distinguish between M. fidelis subspecies. This study suggests that an analysis of M. fidelis microhabitat preference compared to C. aspersum doesn’t need to include subspecies or minor morphological variation. Additionally, if M. fidelis is occasionally misidentified as one of the other Monadenia species, those errors should not significantly impact the data analysis.
Perea, et al. 2007. Journal of Molluscan Studies, 73(1), 39-43.
Perea, J., Garcia, A., Gómez, G., Acero, R., Peña, F., & Gómez, S. (2007). Effect of light and substratum structural complexity on microhabitat selection by the snail Helix aspersa Müller. Journal of Molluscan Studies, 73(1), 39-43. https://doi.org/10.1093/mollus/eyl031
Summary: The authors studied the microhabitat preferences of C. aspersum (formerly Helix aspersa) with respect to light levels and substratum complexity. The snails preferred to rest during the day in the more brightly lit area of the observation chamber and preferred a complex substratum over a smooth substratum. The authors speculated on why the snails might prefer the complex substratum, suggesting it might be because complex substrata retain more moisture or helps snails hide from predators. The finding that the snails preferred the more brightly lit area of the arena was surprising, but could be explained by the fact that the additional light did not elevate the temperature or reduce the humidity.
Relevance: The finding that C. aspersum prefers moderate light over dimly lit areas could partially explain why the snails thrive in residential lawns and gardens. Gardens are typically planted in well-lit areas, but are also regularly watered and therefore are more consistently damp and humid compared to non-maintained areas. If M. fidelis has a different response to light, they might prefer to stay out of residential areas. There may be lots of M. fidelis in the Willamette Valley, but they just aren’t observed in developed areas. As noted in the studies on observer bias in iNaturalist, animals in developed areas are more likely to be observed and recorded.
Severns. 2005. Journal of Molluscan Studies, 71(2), 181-187.
Severns, P. M. (2005). Response of a terrestrial mollusc community to an autumn prescribed burn in a rare wetland prairie of western Oregon, USA. Journal of Molluscan Studies, 71(2), 181-187. https://doi.org/10.1093/mollus/eyi021
Summary: Wetland prairies in the Willamette Valley were historically burned by Native Americans to aid in hunting and farming. Prescribed fires are still used in grasslands to maintain ecosystem structure. Native prairie wetland species may have evolved strategies that allow them to positively respond to prescribed burns, not just survive the burns. For example, a species might rapidly invade burned areas and replace the population that was lost in the burn. The author used a prescribed burn as an opportunity to study the impact on gastropod populations.
M. fidelis was not found in the burned region in any of the 3 years of the study, but 31 individuals were found in the unburned region. Overall, the burned area had fewer gastropods in all three years, suggesting that migration is limited.
Relevance: The finding that M. fidelis did not colonize the burn area suggests that M. fidelis does thrive in disturbed habitats. As the Willamette Valley was developed, it is possible that the preferred habitat of M. fidelis was largely eliminated and that, unlike the introduced snail C. aspersum, it was unable to thrive in residential developments.
Severns. 2006. Veliger, 48(3), 220-227.
Severns, P. M. (2006). Seasonality, habitat preference and life history of some Willamette Valley wet prairie terrestrial molluscs in Western Oregon, USA. Veliger, 48(3), 220-227.
Summary: As of 1994, Oregon wetland prairie in the Willamette Valley was estimated to represent less than 1% of its range in the mid-1800’s, and was considered to be an endangered ecosystem. The wetland prairies have standing water from November through May with small islands that can serve as terrestrial refuges for gastropods. The author used plywood boards to sample snails and slugs, and sampled the plywood boards from October through July for 3 years.
The author found that more snails and slugs were captured as precipitation increased, with snails being active earlier in the fall and later in the spring than slugs. M. fidelis was relatively rare, with only 29 observations over the study period, and were more likely to be found under dry plywood than under plywood in partially inundated areas. M. fidelis were highly motile, often being found at a given site only once, then not found again. The author also reported that M. fidelis was common in a wet prairie site about 0.3 km from the study site, and often found inside the opening of small mammal burrows.
The author discussed comparisons between the wetland prairie gastropod diversity and the diversity of gastropods in the Douglas-fir forests in the Coastal and Cascade Ranges. M. fidelis is one of the few species found in both habitats, but the snails found in wetland prairies are about half the size of snails found in the forests. The author also noted that M. fidelis was also found feeding during the day, although they are reported in the literature as being nocturnal.
Relevance: While M. fidelis is not common in wetland prairies in the Willamette Valley, this study suggests that it was probably much more common in the Willamette Valley historically than it is today. Is the relative absence of M. fidelis in developed areas of the Willamette Valley due to its incompatibility with the landscaping associated with residential areas, or is it being out-competed by C. aspersum in residential areas?