Impacts From Climate Change and Other Threats Increase for At-Risk Canadian Wildlife

Increasing importance of climate change and other threats to at-risk species in Canada

Catherine Woo-Durand, Jean-Michel Matte, Grace Cuddihy, Chloe L. McGourdji, Oscar Venter and James W.A. Grant

Summarized by Anna Geldert

What data were used? In this study, researchers assessed threats to biodiversity in Canada. They drew upon the methods of a previous study by Venter et al. (2006), which recognized six primary threats to biodiversity in Canada: habitat loss, introduced (non-native) species, over-exploitation (i.e., excessive hunting or harvest), pollution, native species interactions, and natural causes. They also assessed the threat of climate change. In total, researchers assessed threats to 820 species from 12 taxa, including: vascular plants (e.g., trees, flowering plants, ferns, clubmosses, etc), freshwater fishes, marine fishes, marine mammals, terrestrial mammals, birds, reptiles, molluscs, amphibians, arthropods, mosses, and lichens. All of these species were classified as at-risk (in decreasing severity: extinct, extirpated, endangered, threatened, or of “special concern”) by COSEWIC (Committee on the Status of Endangered Wildlife in Canada).

Methods: Between October 2018 and September 2019, researchers examined the COSEWIC website for evidence of Venter et al.’s six primary threats, where threatened species and the reasons they are threatened are cataloged . They looked at COSEWIC’s “Reason for Designation” statement, as well as details from the Assessment and Status Report. Any mention of any of the six major threats was recorded, so that multiple threats could be identified for each species. This data was compared to data from Venter et al. (2006) to determine changes in prevalence over time. Additionally, researchers noted mentions of climate change threats to species on the COSEWIC website. Climate change threats were classified as current, probable, or future based on a list of keywords. All seven of the biodiversity threats were assessed over time by comparing their prevalence to species with multiple COSEWIC status reports, including a total of 188 species.

Results: 814 of the 820 species studied were impacted by at least one of the six primary threats to biodiversity. Habitat degradation was the most significant threat, affecting 81.8% of species, followed by natural causes (51.0%), over-exploitation (46.9%), introduced species (46.4%), pollution (35.1%) and native species dynamics (27.2%). This represented an overall increase in threats compared to Venter et al., though introduced species and natural causes were the only threats that increased with statistical significance. Climate change impacted a total of 37.7% of species, with 13.3% of species impacted by current climate change, and 14.7% and 9.7% that will likely be impacted by probable and future climate change, respectively.

The figure shows a bar graph comparing the prevalence of the primary threats to biodiversity in the modern 2018 study and the 2005 Venter et al. study. In the top right corner, a legend indicates that white bars represent data from 2005, which included 488 species total, and black bars represent data from 2018, which included 814 species total. The x-axis shows the biodiversity threats, including habitat loss, introduced species, over-exploitation, pollution, native species interactions, natural causes, and current climate change. For each threat category, a pair of historical and modern bars are shown, with the exception of current climate change, which only has a bar for 2018. The y-axis is labeled “percentage of at-risk species,” and ranges from 0 to 90, increasing at increments of 10. For modern data, habitat loss is the most prevalent threat, affecting 81.8% of species, followed by natural causes, over-exploitation and introduced species, which all affected roughly 45-50% of species. Pollution and native species interactions (affecting 35.1% and 27.2% of species respectively) were moderate threats, while climate change was the lowest, affecting only 13.3%. For the 2005 Venter et al. data, habitat loss was also the most significant threat and was slightly more prevalent than it is today, affecting 83.8% of species. Native species interactions were also slightly higher in the 2005 study than the 2018 study, though not enough to be significant. All other threats were higher in the modern study, though introduced species and natural causes were the only categories that increased with statistical significance.
Fig 1. Percentage of at-risk species in Canada that were impacted by the six primary threats to biodiversity, comparing modern data from December 2018 and data recorded by Venter et al. in June 2005. The modern threat of climate change is also included, though there is no corresponding 2005 record. N represents the number of species (n=488 in 2005, n=814 in 2018).

The analysis comparing threats to species with multiple COSEWIC status reports found an average increase from 2.5 to 3.5 threats per species in newer reports. The prevalence of many threats also increased significantly over time, including a 27.6% increase in introduced species, a 13.3% increase in over-exploitation, and a 10.1% increase in pollution. Mentions of the threat of climate change also increased from 11.7% in the oldest reports to 49.5% in the newest reports.

Why is this study important? This study reveals that threats to biodiversity continue to increase today, despite protections that have been put in place. In particular, the threat of introduced species has increased significantly in recent years, reflecting rises in globalization and human-environmental interactions. Overall, researchers were surprised by the relatively low percentage of species currently impacted by climate change (13.3%), as this topic has gained so much global attention. The authors suggested the unexplained increase in death by natural causes compared to the Venter et al. report may actually account for impacts from climate change, as climate change has increased the severity of storms, droughts, and other weather events worldwide.

The big picture: This study emphasizes the importance of wildlife conservation, in Canada and all over the world. On-going threats such as habitat loss, pollution and overexploitation continue to impact hundreds of species in Canada, so it is likely that stricter protections are needed to enact effective change. Additionally, this study indicates that climate change is among the most significant threats to biodiversity and is projected to continue increasing in prevalence in the future. Although it was not considered to be one of the six primary threats by Venter et al. in 2005, it should definitely be recognized as one today.

Citation: Woo-Durand, C., Matte, J.-M., Cuddihy, G., McGourdji, C. L., Venter, O., & Grant, J. W. A. (2020). Increasing importance of climate change and other threats to at-risk species in Canada. Environmental Reviews, 28(4), 449–456.

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