Eversince the reintroduction of wolves revived the Yellowstone National Park towards the end of the 21st Century, the reintroduction of predators have become common. However, one such reintroduction project has proven controversial and that is in the introduction of Eurasian Lnyx in the Scottish Highlands. Despite resistance from local ranchers, scientists are keen on reintroducing wolves to control the spurging ungulate population. Here we talk about a study which attempts to idnetify the most suitable location for lynx reintroduction in Scotland.
A Study of 3 Potential Sites for Reintroduction
A study attempted to understand the relative probability of population persistence across the three sites , which are Kintyre Peninsula, Kielder Forest and Aberdeenshire. Additionally, the impact of founding population size and multi sites reintroductions on the probability population persistence has been investigated.
The Methodology
Individual based modelling was used in this paper. This is in contrast to the Least Common Pathway used by previous studies (Hetherington et al., 2008). A prominent advantage is that IBM incorporates individual heterogeneity into the model (DeAngelis and Grimm, 2014). Each reintroduction was modelled for 100 replicates of 100 years after reintroduction. The mean number of occupied habitat patches, mean number of individuals and extinction probability over time were calculated at the 100th year.
For single site reintroductions, a founding population of 10 lynx were used across all sites. Meanwhile, a founding population size of 32 individuals were used for the multiple site reintroduction model. This model was based on the simultaneous reintroduction of 18 and 14 individuals at Kintyre and Aberdeenshire respectively. The model was then compared to the single site reintroduction models of both sites with founding population sizes of 32 each.
Kintyre Peninsular proved the best for the Reintroduction of Lynx
The probability of population persistence after 100 years was 83%, 35% and 21% of the replicates in Kintyre Peninsular, Aberdeenshire and Kielder Forest respectively. Furthermore, the mean number of patches occupied and the final population size after 100 years was the highest in Kintyre and lowest at Kielder.
The Kielder Forest has underperformed across all metrics. The model hence concludes that this site has an unacceptably low long term population persistence probability for lynx reintroduction. This has been supported by studies based on prey-based data analysis, which predicts that Kielder Forest can only support between 50-100 lynx (Hetherington and Gorman, 2007). This fall short of the minimum viable population criteria set by IUCN (Hetherington et al., 2008).
However, some studies suggest that the potential of the Kielder Forest as a reintroduction site might be underestimated. The site has less fragmentation and greater woodland cover (White et al., 2022)compared to Aberdeenshire. Additionally, in this model Kielder Forest was underrepresented. Thought it expands to England, the study was restricted to the Scottish region of the forest.
Across all three sites, there was a substantial increase in probability of population extinction between 10-30 years post release, which subsequently stabilized. Elevated extinction probability in all sites was probably associated with lower rates of patch colonisation following the saturation of the original reintroduction habitat. Figure 1 aptly depicts the lack of habitat connectivity amongst sites which demeans population viability.
A Lack of Habitat Connectivity a Potential threat to Reintroduction Success
From Figure 2, there is an evident low patch occupancy probability in the connecting habitat network after 100 years, regardless of release sight. This is consistent with a least common path analysis which predicts the low probability of a viable population being established in the landscape linking the proposed Highlands and Southern Upland sight (Hetherington et al., 2008). In figure 1, greater dispersion probability can be inferred when the lynx was reintroduced in the Kintyre Peninsula. This potentially explains why the region had significantly lower extinction probability relative to the other two reintroduction sites.
A lack of connectivity to other populations have threatened population persistence of reintroduced lynx in the Harz Mountains of Germany. This can be attributed to the lack of gene flow between metapopulations (Mueller et al., 2020). In fact, there has been significant inbreeding noted in the lynx population of the Dinaric Mountains, which is considered amongst the most successful for reintroduction projects (Sindičić et al., 2013).
Founding population size was predicted to have a substantial impact on the success of reintroductions. The single site reintroduction of 32 individuals in Kintyre, had a 10% greater population persistence after 100 years compared to that of a reintroduction consisting of 10 founding individuals. This is unsurprising as past studies of reintroductions in Central Europe have found that increase founding population size resulted in greater genetic diversity (Mueller et al., 2020).
Previous studies have considered Lynx reintroduction to be a success only if there was a probability persistence of 95% after 50 years (Kramer-Schadt et al., 2005). According to this benchmark, only a multi-site reintroduction with 32 lynx is the plausible option.