Analysis of climate change effects on Litoria ewingii is inconclusive due to unreliable data

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1 Cygnus (2014) 1: DOI [ , , , ] RESEARCH ARTICLE Analysis of climate change effects on Litoria ewingii is inconclusive due to unreliable data Danica Delaporte Katie Elliott Catie Fowler Matt White Received: 19 May 2014 / Accepted: 29 May 2014 Subject Editor: Audrey Appudurai, Manuscript Editor: Nicola Mitchell Abstract This study was aimed at assessing the impact climate change is having on the distribution and seasonal events of the Southern Brown Tree Frog, Litoria ewingii. Data was supplied from ClimateWatch in the form of observations recorded by citizen scientists for this analysis. The raw data was analysed by creating maps using the Atlas of Australia s spatial and species occurrence tools and maps were used to determine changes in the distribution and seasonal events of L. ewingii. Due to the unreliability and errors in recording; such as incorrect GPS coordinates, insufficient observation detail and the limited quantity of recordings, there was insufficient data to make a concrete analysis of climate change effects on L. ewingii. No observable changes in the northerly or southerly distribution of Litoria ewingii were identified, as well as no changes in seasonal events being evident. Further research and more reliable, complete data is required for a sufficient investigation of the effects of climate change upon L. ewingii. Keywords Litoria ewingii, Southern Brown Tree Frog, distribution, seasonal events, behaviour, Victoria 1 Introduction Litoria ewingii, more commonly known as the Southern Brown Tree Frog is a tree frog common to the South East coast of Australia and Tasmania. (Frogs of Australia, 2010). It requires a moist habitat for reproduction, and occurs in regions with stable rainfall (Museum of Victoria, 2009). L. ewingii tends to migrate to urban areas due to the abundance of suitable habitats these regions provide, such as lakes and drains. They also reside in forests, farmland and alpine environments (Museum of Victoria, 2009). 247

2 Figure 1 A photograph of Litoria ewingii showing its distinctive markings (image from Frogs of Australia, 2010). L. ewingii is generally light brown in colour, although rare green variants do occur (Melbourne Water, 2012). They have a noticeable white stripe along their jawline from the shoulder to below the eye and a visible eardrum (Frogs of Australia, 2010). The underside of the thighs can range from bright orange to a subtle yellow colour, which can be helpful to identify the species (Frogs of Australia, 2010). L. ewingii ranges from mm in length, with the females being larger than the males (Frogs of Australia, 2010). L. ewingii mate all year round, meaning that they are present in all stages of their lifecycle throughout the year (Frogs of Australia, 2010). They have a very distinct call to attract potential mates, described as a cree-cree-cree-cree, which can be used for identification (Melbourne Water, 2012). This calling is particularly prevalent after rains because they need a moist environment to deposit tadpoles, so they are therefore predisposed to mate when conditions are most favourable (Melbourne Water, 2012). L. ewingii are vulnerable fluctuations in temperature and rainfall due to their dependence on a moist environment for successful reproduction. Climate change is a phenomenon that involves global changes in weather patterns and temperatures. Climate change will result in an increase in global average temperatures, lower rainfall and more frequent and severe droughts as well as heat waves (Environmental Protection Agency, 2010). As a result of climate change, Australia has experienced a net daily increase of 0.9 o c (Climate Change in Australia, 2014). In combination with this, weather patterns have been disrupted, becoming more erratic (Climate Change in Australia, 2014). It is projected that climate change will result in less rainfall in southern areas of Australia including the habitat of L. ewingii (Australian Government Department of the Environment, 2012). Numerous scientific articles have outlined the effect that climate change has already had an impact on species of frogs (e.g. Margolis, 2006; Gelloff 2010). A study on Archey s frog (Leiopelma archeyi) in New Zealand found it was could no longer survive in some environments due decreasses in moisture (Haigh, Pledger and Holzapfel, 2007). Biologists from the University of California Los Angeles (UCLA) found in a study on coqui frogs, that climate change was likely to have altered their calling patterns and therefore changed the 248

3 times in which they reproduced (University of California Los Angeles, 2014). These articles suggest that climate change will have a similar effect on frog other species. The aim of this article is to determine what effects climate change has or will have on L. ewingii. Potentially, climate change could affect the distribution of L. ewingii as they depend on the presence of water and moisture in their environment to survive. It could also affect the reproductive cycle of Litoria ewingii as they only reproduce when there is a suitable body of water present for them to lay eggs in. As a result, a net decrease in rainfall could cause a decrease in potential water bodies. It is expected that L. ewingii might adapt to deal with this lack of rainfall by firstly changing its distribution, favouring areas with suitable rainfall and temperatures. Northern latitudes receive higher rainfall, due to the increasing topicality, so it is thought that L. ewingii would favour northern latitudes over more southerly parts of Australia. It would be expected that L. ewingii would no longer be present in areas where rainfall has decreased. Secondly it is expected that L. ewingii would change certain behavioural characteristics, perhaps only reproducing during the wetter, colder months of the year, as opposed to all year round, to ensure its continued survival. Here we investigate if the distribution or seasonal events of Litoria ewingii have changed and if so if this is likely due to climate change. 2 Materials and Methods ClimateWatch data ( was supplied to BIOL1130 students at UWA as the basis for evaluating our hypothesis. The raw data consisted of records from 2008 to 2013, containing information on behaviour and distribution of L. ewingii across Australia. Other supplied information included the date and time of the observation, location (latitude and longitude), total observed, behaviour and habitat. Data were analysed using Microsoft Excel and all information aside from the catalogue number, latitude, longitude, date and time being removed to simplify the data. The latitude and longitude columns were rearranged on the spreadsheet, so that longitude appeared before latitude. To be able to assess the validity of the data submitted to ClimateWatch it was first filtered and re-evaluated to remove obvious outliers. To do this, the information was put through a spatial tool, which allows a set of points to be imported onto a map of Australia, accessed via the Atlas of Living Australia (ALA) website (Atlas of Living Australia, 2014). This was used to find any unreliable recordings, such as those within oceans or the arid climate of central Australia. Through this process, the observation with the catalogue number 4f4c9336eebda94d e was disregarded as the location entered occurred approximately 1,000 km off the east coast of Australia. Due to the lack of sightings that fall outside of either the Sydney or Melbourne area, these two clusters of information were the baselines for separating the results into north and south zones. In a latitudinal sense, the northern area were sightings that fall between the coordinates and latitude and the southern area will include sightings that fall between the 249

4 coordinates and latitude. This leaves the data with 33 recordings in the northern zone and 26 in the southern zone. As the records for the northern zone do not occur outside of the years 2011 and 2013, this is the range that was assessed. This was used to determine if there were changes to the frequency of calling or mating observations in each region. Data from the northern and southern areas were used to create pie graphs showing the months that observations occurred. Separating the zones into yearly groups was used to indicate if there had been any changes to the frequency of sightings over time. Mean rainfall data were accessed through the Bureau of Meteorology ( A second copy of the map with the observation points was created and another layer was added using ALA s spatial tool showing all of the historic distribution data ranging from the 1870s to the current time. This allowed the ClimateWatch data to be compared to the ALA s historic distribution data. To gather information on the historic changes in distribution of L. ewingii, the ALA species occurrence tool was used. This data was refined by decade, with each decade being plotted on a map and downloaded. These individual decade maps were then compared for historic changes in distribution. This provided the ClimateWatch data with a context for its analysis. Lastly, only the ClimateWatch data was plotted on another map by year to observe any patterns in the short term as opposed to the long term. To do this the dataset was separated by year. There was limited data for 2008 (only two recordings) so these were not included. These separate files were imported onto the ALA spatial tool as different layers, to enable them to be given different colours on the map. 3 Results Table 1 shows how the frequency of recordings changed on a yearly basis. While both data sets contain a similar number of recordings, the northern zone shows a greater number of calling sightings in What can also be established from these tables is there is no discernable linear progression. During 2011, there were a total of 16 observations, seven from the southern zone, all of which are observations of calling. The other nine recordings were from the northern zone, consisting of eight calling observations and one for mating or courting. The yearly change in rainfall is shown in Figures 2, 3 and 4. While 2011 is predominantly an outliner due to the excessive flooding in January, the figures do show a general decline in the yearly average rainfall of south-eastern Australia. 250

5 Table 1 Distribution of behavioral recordings in the northern and southern zones between 2011 and SOUTHERN ZONE NORTHERN ZONE BEHAVIOUR Calling Mating or courting Presence of eggs No description Totals Calling Mating or courting Presence of eggs No description Totals Figure 2 Annual Rainfall Deciles (classification categories) 2011 based on a 112-year climatology of gridded fields from (map from the Bureau of Meteorology, 2013). 251

6 Figure 3 Annual Rainfall Deciles (classification categories) 2012 based on a 113-year climatology of gridded fields from (map from the Bureau of Meteorology, 2013). Figure 4 Annual Rainfall Deciles (classification categories) 2013 based on a 114-year climatology of gridded fields from (map from the Bureau of Meteorology, 2013). A notable point is also the months in which the sightings were focused for each zone. As figure 5 shows, the southern recordings are spread out across almost the entire year. This is in stark contrast to Figure 6, which shows that 88% of the northern sightings are recorded within the months of March and April. 252

7 January March May July august September October December Figure 5 Frequency of sightings in the southern zone with respect to which month they occurred. March April May August Figure 6 Frequency of sightings in the northern zone with respect to the months that they occurred. The distribution of L. ewingii was consistent between the ClimateWatch data and the historical records from ALA (Figure 7). The observations from ClimateWatch were within the parameters of the historical data, however were not distributed over the entire range demonstrated by the historical data. We do see a concentration of recordings around major cities where there is also the highest density of citizen scientists to record these sightings, see figure 8. By comparing the ClimateWatch (2009 to 2013) to historical records from ALA (1960 to 2000), see figure 9, no change in distribution over time is identifiable. Approximately twenty-four of the 114 observations were unreliable; amounting to a reliability rate of approximately 78.94%. 253

8 Figure 7 Map showing the ClimateWatch data (red) and the Atlas of Living Australia Data (blue) for L. ewingii (Atlas of Living Australia, 2014) Blue 2010 Orange 2011 Teal 2012 Pink 2013 Purple Figure 8 Map showing the ClimateWatch data broken down into the year it was recorded in (Atlas of Living Australia, 2014). Data is broken down into four colours dependent of year recorded: blue (2009), orange (2010), teal (2011) and pink (2012) 254

9 Figure 9 Four maps of Australia showing the distribution of L. ewingii over time (a) ClimateWatch , (b) ALA , (c) ALA , (d) ALA (Atlas of Living Australia, 2014). 4 Discussion The ClimateWatch data recorded in Western Australia was disregarded, as L. ewingii is not present in this part of Australia (Figure 7). This was not taken to be a change in distribution, but rather an error in identification, because there was only a small amount of data observing L. ewingii in Western Australia and the Slender Tree Frogs that are found in Western Australia often look like the pictures provided by ClimateWatch for L. ewingii. As data was provided by citizen scientists, not experts, the identity of the recorded frog may be an error of judgement. Historic data from the ALA shows that the distribution of L. ewingii shows has remained stable from the 1870s to the present day. The habitat of L. ewingii is still primarily located in areas where there is significant rainfall, namely Tasmania and south east Australia. By studying the more recent ClimateWatch data it can be concluded that there has been no shortterm difference in the distribution of Litoria ewingii from 2009 to The observations from each year all remain within the same clustered areas, being mainly Victoria and Sydney. 255

10 Through this consistency of the distribution patterns it can be inferred that there has been no change to the reproductive cycle of Litoria ewingii. Reproduction is still occurring under normal conditions in the expected habitat, leading us to conclude that that the species has not been impacted by climate change in any recognisable way. Secondly most records for L. ewingii of calling males have been recorded consistently throughout the year. These records represent a high likelihood of year round breeding, which corresponds to the expected breeding patterns. From the ClimateWatch data it can be concluded that there has been no noticeable effect of climate change on L. ewingii and its distribution or reproductive cycle thus far. However, the lack of data from ClimateWatch affected the reliability of our results. Although there are reasons for the lack of ClimateWatch data outside of urban areas, this meant that our conclusions were inferred rather than be based on actual data points. The results would have been more reliable had ClimateWatch been able to collect more data from the full distribution of L. ewingii, not just urban and peri urban regions, to provide a clearer image of the current distribution. The unreliable data was determined by observing the misappropriation of coordinate points, incorrect identification of the frog species and the occasional lack of useful information in the observations submitted. By filtering the data that met our conditions, those observations that remained could tentatively be considered as reliable. To remedy future mistakes of these kinds, citizens should observe the frog. It is noted that several of the observations were of the calling individuals, where the frog is often not seen. It is possible that relatives of L. ewingii, such as Litoria paraewingi or Litoria verreauxi, are heard instead, resulting in misidentification. Adding to this problem is the lack of information provided in recorded observations that can confirm the reliability of the data. If a record of a frog cannot confirm the behavior, occurrence, number of individuals or habitat, then data is virtually useless as there is virtually no method by which observation can be confirmed as correct. Within the ClimateWatch data, approximately 24 of the 114 observations were unreliable; amounting to a reliability rate of approximately 78.94%. This figure excludes observations where the frog was not visible. Such observations are otherwise detailed in the other categories of information, but it cannot be certain that the species was indeed L. ewingii. Due to problems in the ClimateWatch data for L. ewingii, primarily due to distributional, behavioural or quantitative data recorded that is anomalous for species, the data does not accurately of L. ewingii habits. For example, the data showed an inconclusive relationship between longitude and seasonal events. Table 1 shows that in 2012 there was not a single sighting in the northern zone, while in the very next year we see a jump to 24 sightings. As there were no related weather changes that could account for such a large variation, this change in recordings cannot be reasonably linked to climate change. From this we concluded that L. ewingii sightings in the ClimateWatch data are not an indication of the actual number of frogs present. 256

11 A study on Archey's frog (Leiopelma archeyi) conducted in New faced a similar issue (Haigh, Pledger and Holzapfel, 2007). Simple observations of the frog were not sufficiently reliable to allow hypotheses to be testes as there was too much room for human error. Therefore more concentrated data collection was done over five intensive trips during a twoyear period that resulted in more reliable source of information. As frogs have shown to be harder to identify then most animals, due to similar mating calls and cryptic colouration that can make them almost indistinguishable from other species, data should be sourced from more reputable scientific sources, rather than from casual observers. Another restriction upon concluding whether climate change is affecting L. ewingii, is that ClimateWatch data is restricted to between 2008 and Six years is insufficient time to observe many changes in distribution or in seasonal events. Although ClimateWatch data can be compared to historical data, a longer period of recent data would have improved this investigation. The best gauge would have been 10 to 20 years of ClimateWatch data. This is evident when looking at research conducted by Narins and Meenderink (2014) who s study focused on the altitudinal changes of the Puerto Rican coqui frog (Eleutherodactylus coqui) in response to climate change, in particular temperature increases. A range of 23 years was used to accurately evaluate the changes so that no short term outliers were included in the final results. We believe that this is a more suitable time frame through which to evaluate true climate change consequences. In conclusion we believe that currently the southern brown tree frog is a poor indicator species for ClimateWatch, as the observations have been too sparse in information and credibility to be reliable. This has made it impossible for us to draw any conclusions that can be based on solid scientific principles. Acknowledgements We would like to thank ClimateWatch and the citizen scientists for supplying the data for this analysis. We would also like to thank the Atlas of Living Australia for the use of the mapping functions this resource offers, as well as for the data that was accessed for our study. In addition, we would like to thank the Bureau of Meteorology for supplying annual rainfall maps that were essential to our investigation. Thank you also to the peer reviewers for contributing well thought-out and detailed suggestions. References Atlas of Living Australia Atlas of Living Australia [Online]. Available: [Accessed 03/ ]. Australian Government Department of Environment Rainfall [Online]. Available: [Accessed 18/ ]. Bureau of Meteorlogy Annual climate statement 2013 [Online]. Available: [Accessed 04 April 2014]. Climate Change in Australia Climate Change in Australia [Online]. Available: [Accessed 18/ ]. ClimateWatch Southern Brown Tree Frog [Online]. Available: [Accessed 31/ ]. Environmental Protection Agency Climate Change: Basic Information [Online]. Available: [Accessed 15/04/ 2014]. 257

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