The Canada Lynx (<em>Lynx canadensis</em>) of Isle Royale: over-harvest, climate change, and the extirpation of an island population

Abstract

In the 1930s, the Canada Lynx (Lynx canadensis) was extirpated from Isle Royale, a 535-km 2 island located in western Lake Superior, 22 km from the Ontario and Minnesota shorelines. The first half of the 20th century was a time of change on Isle Royale as Caribou (Rangifer tarandus) disappeared, Coyotes (Canis latrans) briefly appeared, Moose (Alces americanus), Grey wolves (Canis lupus), and Red Foxes (Vulpes vulpes) became established, and the habitat was altered by fire, logging, and over-browsing. although these changes may have contributed to the demise of the Canada Lynx, our results suggest that over-harvest was a primary cause. assuming a peak carrying capacity of 75 Canada Lynx and harvest rates comparable to those reported from 1890-1935, a population viability analysis indicated that the island population had a 0% chance of surviving 50 years. The analysis also indicated that, even in the absence of harvest, the population had only a 14% chance of persistence for 250 years. however, when 10 Canada Lynx were added to the modeled population every 10th year, the probability of persistence increased to 100%. Our analyses suggest that the island's Canada Lynx population maintained itself by periodic immigration across an ice bridge; therefore, natural recolonization should be possible. however, the probability of ice-bridge formation has declined from 0.8 in the winter of 1958-59 to 0.1 in 2012-13, likely as a result of climate change. The Isle Royale situation exemplifies another impact of climate change and the possible need to augment populations to mitigate the loss of connectivity.

Irruptions: evidence for breeding season habitat limitation in Piping Plover (Charadrius melodus)

“…Some storms overwash barrier island habitats and create bayside foraging habitat and can also increase dry sand habitat ( Fig. 2; Leatherman 1979, Maslo et al 2019, Walker et al 2019). On the Missouri River, high outflow from the Gavins Point Dam and flooding created new, unvegetated sandbars (USACE 2012), resulting in a population increase (Fig.…”

“…If densities in available habitat limit a population, improvement of existing habitat or creation of new habitat should increase carrying capacity, thus resulting in population growth. Alternatively, some species declines have been driven by density-independent factors, including climate (Putman et al 1996), pesticides (Grier 1982, Buehler 2000, White et al 2002, Shields 2014, poisons (Nadjafzadeh et al 2013), and overharvest (Chan et al 2014, Wittemyer et al 2014, Hamilton et al 2015, Licht et al 2015. In such cases, when habitat availability remains abundant or is restored, and reproduction and mortality return to more normal levels, populations rebound.…”

Dynamic colonization history in a rediscovered Isle Royale carnivore

“…1966, again going undetected for several decades 34 . Lastly, martens could have colonized Isle Royale in the late 20 th century via Ontario, the closest mainland (35 km), possibly using an ice bridge across Lake Superior, as has occurred for other Isle Royale carnivores 29 , 48 . Our MIGRAINE estimates indicate martens on Isle Royale experienced a significant bottleneck within the last generation (i.e.…”

“…1991. Historical ice data shows numerous ice bridges connected Isle Royale to mainland Ontario in the 10 years preceding marten rediscovery 29 , thereby making a natural colonization possible. It is worth noting, however, that martens are the most widely translocated carnivore in North America 50 and have a history of human-assisted island colonization – both sanctioned and unsanctioned 19 .…”

“…Indeed, historical assemblages of vertebrates have been constructed entirely from museum surveys and anecdotal accounts 27 , 28 . Furthermore, lake ice formation, a primary mode of colonization to Isle Royale, has become increasingly stochastic due to regional climatic warming, potentially disrupting historical connectivity to the mainland 29 . Thus, the restoration of Isle Royale fauna is confounded by uncertainties in both historical community composition and future colonization potential 26 .…”