The relationship between non-suicidal self-injury and suicidality

The overall purpose of this study was to explain the overlap and distinctiveness of non-suicidal self-injury (NSSI) and suicidality from a diathesis-stress perspective. The first part of this study evaluated the third variable theory as an explanation for the high rates of lifetime co-occurrence between NSSI and suicidality. Specifically, it was hypothesized that these forms of self-harm share a common vulnerability profile comprised of five affective, cognitive and behavioural diatheses. The second part of this study tested the hypothesis that NSSI and suicidality become distinguishable on the basis of immediate, proximal stressors, namely psychache and survival and coping beliefs (SCB). Participants (N = 262) were community individuals aged 16-24 years who reported either no history of self-harm (i.e., no history of NSSI, suicidality, or both), a history of NSSI, suicidality or both, or current NSSI-only or current NSSI+suicidality. They were recruited online to complete an online battery of questionnaires. Using a set of discriminant function analyses, it was found that the vulnerability profile was unable to distinguish between the three self-harm groups, but was able to differentiate the no self-harm group from a collated self-harm group. Result patterns were also analyzed for gender differences. It was also found that a current NSSI+suicidality group exhibited significantly higher psychache and lower SCB (for women only) than a current NSSI-only group. These results suggest that NSSI and suicidality may tend to co-occur because they have similar long-term diatheses, but that they may become more distinct with respect to immediate psychological stressors.

The effects of the non-native invertebrate predator Bythotrephes longimanus and declining aqueous calcium on crustacean zooplankton communities in Canadian Shield lakes

Over the last several decades, human activities have resulted in environmental changes that have increased the number of stressors that can act on a single environment. In Canadian Shield lakes, two recent stressors, the invasion of Bythotrephes longimanus and calcium decline, have been documented. Widespread acidification of hundreds of North American lakes has resulted in the precipitous decline of lake water calcium concentration. Crustacean zooplankton with high calcium demands are likely to be vulnerable to calcium decline, especially <1.5 mg Ca/L, where survival and reproduction rates are reduced. These taxa are also vulnerable to predation by Bythotrephes that has been implicated in the loss of pelagic biodiversity in soft water lakes. Despite laboratory and field studies aimed at understanding the independent impact of these stressors, it is unclear how their co-occurrence will influence community response. Using a combination of data from a large regional lake survey and field experiments, I examined the individual and joint effects of Bythotrephes and calcium decline on native zooplankton community structure. Results demonstrated that much is known about Bythotrephes and our findings of reduced total zooplankton and species richness, due to the loss of Cladocera, are consistent with field surveys and other experimental studies. While we did not detect strong evidence for an effect of calcium on zooplankton using the lowest calcium concentration among invaded lakes (1.2 mg Ca/L), there is evidence that, as lake water calcium concentrations fall <1 mg Ca/L, per capita growth rates of a broad variety of taxa are expected to decline. At the regional scale, negative effects of Bythotrephes and calcium on abundances of small cladocerans and Daphnia pulicaria, respectively, were in agreement with my experimental observations. We also observed significant interactions between Bythotrephes and calcium for a broad variety of taxa. As Bythotrephes continues to spread and invade lakes that are also declining in aqueous calcium, both stressors are likely to amplify negative effects on Cladocera that appear the most vulnerable. Loss of these important zooplankton in response to both Bythotrephes and calcium decline, is likely to lower zooplankton productivity, with potential effects on phytoplankton and higher trophic levels.