by Mark Lawler
The impacts of contemporary climate modify on biodiversity are undeniable too emphasize the critical demand for understanding biotic responses to past times shifts inwards climate, too inwards applying that cognition to guide electrical current dry ground management decisions [1, 2]. The basis is experiencing human-induced global ecological transformations. These changes accept led to a global biodiversity crisis where the species lost charge per unit of measurement exceeds the electrical current background charge per unit of measurement of 0.1–1.0 extinctions/million species years [3, 4, 5, 6]. Mathematically speaking, this way that if at that topographic point are a 1000000 species on the earth, i would larn extinct every year, piece if at that topographic point was exclusively i species it would larn extinct inwards i 1000000 years, etc. [6]. One of the species currently threatened past times these ecosystem changes is caribou, which are members of the cervid (deer) family, known inwards Europe equally reindeer (Figure 1). Caribou accept a Holarctic distribution too incorporate v recognized subspecies: R. t. granti; R. t. groenlandicus; R. t. pearyi; R. t. tarandus too R. t. caribou, which has iii ecotypes the migratory barren-ground, the mount or woodland (montane), too the forest-dwelling [7].
Caribou survived the tardily Pleistocene extinction, but today, inwards the confront of a warming planet which increases the sensibility of the surface area together alongside the induced ecosystem changes, it has an uncertain future. Over the past times xxx years, of import changes were observed inwards the caribou community of Canada. For example, the Labrador George River herd had 800,000 animals at their peak inwards the tardily 1990s, but now, xxx years subsequently the position out declined past times 99% to only 5,500 animals. In Newfoundland, numbers of woodland caribou accept declined from 95,000 to nigh 30,000 today [8, 9]. What is causing this decline? Is it a natural "boom/bust" cycle, anthropogenically driven, or a combination of anthropogenic too natural causes? How tin the fossil tape assist shed lite on these questions?
Fig. 1: Woodland caribou (Ryan Hodnett / CC BY-SA )
Caribou Decline Today
The woodland (boreal) caribou (R. t. caribou) is listed equally a threatened species inwards Newfoundland too Labrador [9]. A 2015 written report produced past times the Department of Environment too Conservation of Newfoundland concluded that the rapid turn down too slow-to-recover numbers of Newfoundland's caribou are role of a long, natural wheel of unsustainably high populations during the 1990s followed past times a rapid turn down [8]. The reasons for these changes were the wide shifts inwards habitat use, e.g., diet became less selective alongside to a greater extent than poor-quality foods. Body size was reduced, too inwards some herds, calf recruitment (the per centum of calves that hold out to i yr of age) decreased. Within 10 years, the Newfoundland caribou population was reduced past times half.
The National Recovery Strategy for Labrador's caribou developed past times the authorities of Labrador suggests that ranges (areas inwards Labrador where caribou are industrial plant life today) alongside less than 10% disturbance accept a greater than 90% likelihood of stable or increasing population growth based on the disturbance–recruitment human relationship derived from ranges throughout Canada [9]. In other words, the lesser the amount of human disturbance, the greater the odds that caribou populations tin increment too stabilize. Despite hit disturbance betwixt 5–9%, iv out of v populations of woodland caribou inwards Labrador were inwards turn down [9]. A combination of factors from disturbance to contest too range-specific environmental atmospheric condition may accept the most explanatory power.
Caribou inwards Prehistorical Times
The speedily changing climates of the Pleistocene-Holocene Transition (PHT) re-organized ecosystems, altered species abundances, too forced large-scale movements of taxa, thereby changing biodiversity distribution patterns [10, 11]. The PHT is defined hither equally the fourth dimension betwixt fifteen ka cal BP (thousand years earlier present) too eleven ka cal BP. While straight analogs cannot live made betwixt the global environmental changes that took house at the PHT too what is occurring today, assessments of how fauna reacted to these rapid ecosystem changes tin live made.
Fig. 2: Late Pleistocene fossil caribou localities, courtesy of Mark Lawler
In North America, caribou are believed to accept congregated inwards a refugium (favorable surface area where species accept survived periods of glaciation too ecological transitions during the tardily Pleistocene) due south of the Laurentide H2O ice canvass (LIS) during the lastly glacial maximum (LGM) too early on retreat of the LIS (20 ka cal BP-2 ka cal BP) (Fig. 2). At around 12 ka cal BP, the population dissever into a northern too southern ecotype equally it recolonized late deglaciated terrain [13]. It had been presumed that this late-glacial refugium was located along the southern border of the LIS inside the tundra/taiga ecozone. However, few fossils accept been industrial plant life inwards this location, alongside most caribou remains industrial plant life hundreds of kilometers due south of the LIS, some equally far due south equally Alabama [14]. Late-glacial caribou remains accept been industrial plant life inside the Appalachians leading some to require that the principal concentration of caribou prior to eleven ka cal BP was inwards an Appalachian refugium [13]. A montane strategy of height migrations was employed to avoid contest too predation at lower elevations decreasing the potential of resources contest too option prey scenarios [7; 13; B. Gordon, personal communication, Feb 18, 2019].
Outlook & Future Work
We may non live able to decide how all species, populations, too clades volition respond to
anthropogenic perturbations, but nosotros tin predict how some species tin respond to
anthropogenically forced ecological modify past times examining those that survived the PHT [12]. Caribou inwards eastern North America tin live considered i of these extant winners. Analysis of the paleobiology too ecology of caribou is needed to empathize why this species survived the PHT piece other megafauna (mastodon too mammoth, for example) did not.
What was unique well-nigh caribou that allowed them to hold out the terminal Pleistocene extinctions inwards eastern North America too hold out at that topographic point until existence extirpated from the part inwards the 19th century? Unlike mastodons, alongside which caribou shared the landscape inwards the tardily Pleistocene of eastern North America, caribou remains are far less numerous, fragmentary, too oftentimes consist of calcined os [15]. The lack of well-provenienced, feasible (for analysis), tardily Pleistocene caribou remains makes it challenging to respond the interrogation above.
The interrogation of caribou persistence at the PHT continues to live investigated equally role of my dissertation research. In a futurity spider web log post, I volition verbalize over how using the fossil tape tin assist address the interrogation of caribou persistence inwards the past, too their survival into the futurity inwards a speedily warming world. I volition verbalize over the importance of assessing the energetic requirements of R. t. caribou, an essential metric equally temperatures move along to rise, placing high latitude taxa such equally caribou nether to a greater extent than meaning threat of ecological disturbance including loss of habitat, increased harassment from oestrid flies leading to reduced calf recruitment, increased contest from other megaherbivores, too increased predation. I volition also verbalize over how analyzing the life-history traits (e.g., fecundity, gestation length, dispersal, adult size, mass) volition Pb to a ameliorate understanding of how these traits helped caribou hold out the tardily Pleistocene extinction too tin assist them too other taxa persist through the electrical current biodiversity crisis.
Stay tuned…
Mark Lawler, a paleobiologist/paleoecologist completing his doctorate inwards Environmental Studies
at Antioch University New England, USA
If you lot accept questions or comments concerning Mark's post, delight move out a comment below, or shipping him an email. You tin also follow his enquiry on ResearchGate, LinkedIn or Twitter.
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