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Variation of the Refuge Depth of Salamanders at the Morgan Arboretum

Overview

Although they are hidden amongst the leaf litter and often hard to spot, salamanders are key subjects in many ecological studies. While clearing out rocks from a site at the Morgan Arboretum, one of our team members noticed an abundance of salamanders underneath rocks located deeper in the soil. According to studies completed about the vertical distribution of salamanders within the soil, they were found to take refuge at an average depth of 5 inches. [12] Our team of five undergraduate students at McGill University set out to find a correlation between the occurrence of salamanders at the Morgan Arboretum and the depth of refuge within the soil.  Through our twitter page (@Redsalamanders), we received tips and guidance from Salamander experts along the way!

General natural history of salamanders

Salamanders are classified as amphibians and belong to the order of Caudata. They generally possess long bodies, long tails, short and weak limbs, as well as thin skulls. They are recognized as a monophyletic group, meaning they arise from a single ancestor. More than 400 species of salamanders are distributed within Northern, Central and Southern America, Europe and temperate Eastern Asia [7].

Most species of salamanders in North America belong to the Plethodontidae family and lack gills and lungs. Therefore their skin must be kept moist to allow gas exchanges to occur. Thus, many species belonging to this family living on the woodland floor seek moist habitats and hunt invertebrates in the leaf-litter during rainy conditions. In dry conditions they tend to take refuge underground or underneath logs and rocks. The skin of Salamanders also contains many colour-producing pigments, making some species brightly-coloured, having spots or other markings on their bodies. In general, Salamanders are carnivores and depend heavily on vision and smell in order to hunt their prey. However, they are also a source of prey to many other species, and use the toxic mucous layer on their skin to make them toxic to defend against predators. [7].

Salamanders are believed to play a role in carbon storage and the nutrient cycle within temperate forests due to their large number and biomass [6].  For example, salamanders uptake nutrients and energy through the consumption of their prey; some of this is used to create new tissue, while the rest is given to their environment through dead tissue, excreted waste, heat and respiration. This waste is easily used by microbes and primary producers. It can increase decomposition and plant growth in some systems. Since they can achieve surprisingly high densities in these forests, these salamanders also regulate invertebrate populations, as well as leaf-litter decomposition [6].

Salamanders of interest

 

Of the eight salamander species present in southern Quebec, the arboretum has recorded sightings of only two, the eastern red-backed salamander (Plethodon cinereus) and the blue-spotted salamander (Ambystoma laterale) [1, 10]. These two species are the focus of our study, and although they have similar diets, distributions, and habitats there are differences between them that are worth discussing.

The Eastern Red-backed Salamander

The eastern red-backed salamander is a member of the lungless salamander family (Plethodontidae). Adults are between two to four inches and have a clearly defined red stripe that runs from the base of its neck to the beginning of its tail [5] (Fig. 1).

salamander-figure1

Fig.1. Photo of Red-backed Salamander that was found underneath a rock in a deciduous stand at the Morgan Arboretum.

Similar to most salamanders, the eastern red-backed is an insectivore that feeds on several insect orders including flies (Diptera), beetles (Coleoptera), and ants and wasps (Hymenoptera) [4]. The redback diet is very restricted by prey size, as juveniles they feed on notably smaller prey than adults because of the size of their jaw [9]. Eastern red-backed salamanders feed in the leaf litter and under refuges such as rocks and logs. Unlike the blue-spotted salamander, the eastern red-backed is a purely terrestrial species and even lays its eggs on land. [5] See our video showing a Red-Backed Salamander moving through the leaf litter of a deciduous stand.

The Blue-Spotted Salamander

The blue-spotted salamander can be found between the southern tip of the Hudson Bay and southern New Jersey and throughout areas surrounding the great lakes [11]. Comparably to the eastern red-backed, the blue-spotted salamander lives on the floor of temperate rainforest. However, they live on land and in water at different stages of their lives, and therefore spend their terrestrial life beside breeding ponds [2]. Its physical appearance is also drastically different from the red-backed. The blue-spotted is between four to five inches long with distinctive bluish-white spots along the side of the body and tail and has relatively long toes [5] (Fig. 2). Although the blue-spotted salamander also feeds on invertebrates, much of its diet is made of woodlice relatives (Isopoda), snails and slugs (Gastropods) and terrestrial worms (Oligochaeta) which is very different from the red-backed’s diet [3].

salamander-figure2

Fig.2. Photo of a rare Blue-spotted Salamander that was found hiding underneath a log in a deciduous stand at the Morgan Arboretum.

 

Methodology & Question

Taking into account our preliminary observations and research, our group proposed the following research question: Is the occurrence of Caudata related to depth of refuge within the soil? Based on initial observations, it was hypothesized that the occurrence of Caudata increase with increasing depth of refuge in the soil. In order to answer our question, we randomly selected 12 plots at different locations in the Morgan Arboretum that measured 8m X 8m. Experimentation took place during three-hour lab periods once a week for three consecutive weeks. Once the plots were located using a GPS, the boundaries of the plot were measured by two people using an 8m measuring tape and the extremities marked with flagging tape. The rocks and logs within the plot were then flipped over and their depths were measured from the deepest point in the soil. The objects that were flipped were subsequently returned to their original positions. If a Salamander was located, it was placed next to its original rock or log to prevent injury.

figure3-map-good

Fig. 3. Map of the arboretum. Shown above are the 12 plots that were randomly chosen, in order to obtain results that were not biased. Plots were chosen on a variety of trails with various soil types, as well as a combination of deciduous and coniferous stands.

salamander-figure4

Fig. 4. Group member using a ruler to measure the depth of a rock that had been flipped over. A Red-backed Salamander was spotted underneath the rock.

Results:

There have not been any outstanding trends in our results thus far comparing abundance of salamanders to the depth at which they were found.  However, an obvious correlation can be seen between amount of salamanders found and the area of the plot studied; some plots had little to no salamanders and others had one under almost every rock.  The observed trend is due to the randomness in location of our plots as the areas having different properties.  These include abundant tree type, soil type, soil acidity, moisture, density of soil, amount of leaf litter, etc. [8] These factors, along with temperature and rainfall, explain this trend as samples were taken on separate days.

Problems faced while collecting data

Some of the problems faced while collecting data include the amount of leaf litter on the floor making it difficult to locate rocks and logs to turn over, rocks and logs being too heavy or large to move, and rocks and logs sitting directly on top of soil making a measurement of depth impossible. Furthermore, some plots did not have enough rocks or logs to come to an accurate conclusion about the relationship of depth to number of salamanders in that area. Lastly, some salamanders were either dead or immobile at the time when they were found and others were too difficult to see or escaped before an accurate observation could be made.

 

References

  1. Atlas des amphibiens et des reptiles du quebec. 2014. Qc: Société d’histoire naturelle de la vallée du Saint-Laurent; [updated 2014 Sep 30; accessed Oct 31 2017]. http://www.atlasamphibiensreptiles.qc.ca/.
  2. Belasen A, Burkett E, Injaian A, Li K, Allen D, Perfecto V. 2013. Effect of sub-canopy on habitat selection in the blue-spotted salamander (ambystoma laterale-jeffersonianum unisexual complex). Copeia[Internet]. [cited 2017 Oct 30]; (2):254-261. Available from: http://www.bioone.org/doi/pdf/10.1643/CE-12-051
  3. Bolek MG. 1997. Seasonal occurrence of cosmocercoides dukae and prey analysis in the blue-spotted salamander, ambystoma laterale, in southeastern wisconsin. The Helminthological Society of Washington [Internet]. [cited 2017 Oct 30]; 64(2):292-295. Available from: http://bionames.org/bionames-archive/issn/1049-233x/64/292.pdf
  4. Burton TM. 1976. An analysis of the feeding ecology of the salamanders (amphibia, urodela) of the hubbard brook experimental forest, new hampshire. Journal of Herpetology [Internet]. [cited 2017 Oct 30]; 10(3):187-204. Available from: https://www.jstor.org/stable/pdf/1562980.pdf
  5. Conant R, Collins JT. 1998. A field guide to reptiles & amphibians : Eastern and central north america. NY: Hought Mifflin Company.
  6. Hickerson C.M., Anthon, C.D., & Walton B.M. (2017). Eastern Red-backed Salamanders Regulate Top-Down Effects in a Temperate Forest-Floor Community. Herpetologica [Internet]. [cited 2017 Oct 30]; 73(3), 180-189. Available from: doi:10.1655/HERPETOLOGICA-D-16-00081.1
  7. Holman JA. (2006). Fossil Salamanders of North America.Bloomington [Internet]. IN: Indiana University Press. [cited 2017 Oct 30]. Available from: http://www.iupress.indiana.edu/product_info.php?products_id=22803
  8. Jaeger RG. (1980). Microhabitats of a Terrestrial Forest Salamander. Copeia.[Internet]. [cited 2017 Oct 30]; 2(1980): 265-68. Available from: doi:10.2307/1444003.
  9. Maglia AM. 1996. Ontogeny and feeding ecology of the red-backed salamander, plethodon cinereus. Copeia [Internet]. [cited 2017 Oct 30]; (3):576-586. Available from: https://www.jstor.org/stable/pdf/1447521.pdf
  10. Reptiles & amphibians. 2010. Qc: Mcgill Morgan Arboretum; [updated 2010 Jan 22; accessed Oct 31 2017]. http://www.morganarboretum.org/nature-fr/104-nature.html.
  11. Ryan KJ, Zydlewski JD, Calhoun AJK. 2014. Using passive integrated transponder (pit) systems for terrestrial detection of blue-spotted salamanders (ambystoma laterale) in situ. Herpetological Conservation and Biology [Internet]. [cited 2017 Oct 30]; 9(1):97-105 Available from: http://www.herpconbio.org/Volume_9/Issue_1/Ryan_etal_2014.pdf
  12. Frieda FB. (1961). The Distribution of the Red-Backed Salamander, Plethodon C. Cinereus, within the Soil. Journal of Ecology [Internet]. [cited 2017 Oct 30]; 42(2):681-698. Available from: doi:10.2307/1933498

 

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