Friday 12 July 2019

Taxon Surrogate Profiles North America # 2: Camelidae

         One of only three families of Artiodactyls to have evolved in North America (the others being the Antilocapridae and Tayassuidae), the Camelidae are amongst the most distinctive members of the even-toed ungulates, being more distantly removed from cattle, deer, and pigs than even whales are. Despite having originated in North America, and being found there exclusively for roughly ninety percent of their existence, the Camelidae no longer have native representatives on the continent, and haven’t for over ten thousand years. During the late Pleistocene, both living tribes of Camelids, the Camelini and Lamini, were found in North America, with four to six genera split between the two groups. The camels were represented by Camelops, Paracamelus, and Titanotylopus (possibly distinct from Gigantocamelus, unclear), and the llamas by Hemiaucheniaand Palaeolama
Camelops hesternus, known colloquially as the western camel, would have been roughly the same size as members of the living genus Camelus, and was a typical inhabitant of dry, open habitats in western North America up until the Pleistocene-Holocene transition. Paracamelus, the genus to which the modern species owe their ancestry, could still be found in the more northern areas of the continent, in the form of Paracamelus gigas, during the middle Pleistocene, though their exact date of extinction remains unclear. Paracemelus crossed the Bering land bridge around six million years ago, at which point it quickly spread across the arid and semi-arid regions of the Old World and eventually evolved into the modern Camelus, the genus to which living Dromedary and Bactrian camels belong. Camelops also ranged into these areas during interglacials, but was not present during the colder stages and consequently it never crossed the Bering strait into Eurasia. Titanotylopus nebraskensis was the largest of the Pleistocene camels, standing three and a half meters high at the shoulder, and weighing almost three metric tonnes. The official date of extinction for this group is sometime in the Irvingtonian period, but some recent finds from Alberta may push their occurrence well into the Rancholabrean. All three of these Cameline genera are thought to have been open-country browsers, much like the living genus. Hemiauchenia contained many species very similar to the llamas and alpacas (plus their wild counterparts) that are still with us today, and in fact these animals are the descendants of members of this genus which colonized South America during the Great American Interchange roughly five million years ago. In the late Pleistocene one species, Hemiauchenia macrocephala, which would have resembled a wild llama but about thirty percent larger, was still quite common across western and southern North America. Palaeolama was also a member of the Lamini tribe, but unlike Hemiauchenia or its descendants, which are/were largely mixed feeders adapted to open environments, Palaeolama appears to have been a strict browser adapted to closed or semi-closed forest environments, a niche not filled by any living camelid today. The only species of this genus that made it to the Pleistocene-Holocene transition in North America was Palaeolama mirifica, which was found in the American southeast. Members of both Hemiauchenia and Palaeolama also existed in South America during this period, as did a poorly described genus known as Eulamaops, an alpaca-sized camelid that appears to have been an open-country browser.
Ever since Pleistocene Rewilding first arose as a concept, camels (alongside horses, lions, cheetahs, and elephants), have been touted as a no-brainer for reintroduction to the American west. Generally, most people who subscribe to the idea of trophic rewilding using pre-Holocene baselines believe that camelids belong in North American ecosystems, but correct implementation of said introduction evades common consensus. Some say that Dromedaries (Camelus dromedarius), with their ease of availability, are the best choice. Others say domestic Bactrians (Camelus bactrianus), which are also available commercially (albeit less cheaply) and which originate from very similar habitats and climates to those found in western North America, would be preferable. My belief is that the best options for a combined Camelops-Paracamelus-Titanotylopus substitute is the last wild member of the Camelini, the wild Bactrian camel, Camelus (bactrianus?) ferus, and there are several reasons for this. The first is that the wild Bactrian is heavily threatened in its native habit in China and Mongolia, being considered Critically Endangered by the IUCN, with just over a thousand individuals remaining, split between two or three populations, and only one captive breeding program. The creation of a fourth population on the Great Plains, which is closer to what is generally considered ideal camel habitat (as opposed to some of the extreme desert habitats where human activity has pushed them) and where poaching and hybridization with domestics would largely be a non-issue, could potentially be very beneficial to the future of the species.
The second reason why wild Bactrians might be preferable is that, as a truly wild and non-domestic species, they are probably better prepared for wild-living in a landscape with significant predator densities. It is true that domestic camels go feral quite easily, but their interaction with large predators is not well-documented, with the most famous feral camel population, the Australian Dromedaries, not having to deal with anything larger than a dingo, which is completely ineffectual at controlling camel numbers. Camels in East Africa occasionally have conflicts with lions, but these populations are rarely considered feral, and individuals are generally quite helpless in their behaviour. Wild and domestic Bactrians may deal with wolves occasionally, but these mostly target calves, with the same being true for bears. In the distant past (before the Holocene), wild camels would have had to deal with cave lions (Panthera (leo?) spelaea) and hyenas (Crocuta crocuta spelaea), and in historic times when wild camels still roamed the Caspian region they would have occasionally experienced predation by tigers and leopards. The camel’s size and aggressiveness are its main defences against predators, which will usually target smaller prey when available. 
Obviously obtaining wild Bactrians would be difficult (though starting a captive population really should be a priority regardless) but I think it’s alright to play the long-game in this case. Projects in Mongolia have shown that they can be kept and bred in captivity which, regardless of rewilding potential, would possibly represent an opportunity to begin replacing domestic Bactrians and Dromedaries (both of which have little conservation value) in accredited zoological collections with wild Bactrians. A similar process is ongoing with the replacement of captive collared peccaries (Pecari tajacu) with Chacoan peccaries (Catagonus wagneri), due to the Endangered status of the latter species, compared to the Least Concern status of the former species. Breeding the wild Bactrian in Canada, Mexico, and the US would be a great first step for a potential introduction to wild areas in the North American continent, as well as a potentially crucial step in the preservation of the species.
Reintroducing the Lamines to North America is considerably less complicated. Wild llamas (guanacos, Lama guanicoe) and wild alpacas (vicunas, Vicugna vicugna) are both considered Least Concern. Consequently, even though their domestic counterparts would still be easier to obtain, it makes far more sense to acquire wild animals, as it would be completely feasible even in the short-term. There exists already a large population of guanacos both in zoos and in private collections in North America, and a wild population could conceivably be sourced from these institutions. Vicunas do exist in captivity in North America, but in very low numbers, and more would probably have to be sourced either from the wild or from zoological collections in Europe, where the species is more numerous. Both are native to similar habitats to those found in western/southern North America, and guanacos also inhabited similar climates to that of the south-eastern US in prehistoric times. Both species are adapted to predation by large cats, such as pumas and in some places jaguars, and to a lesser extent also bears and large canids (of which there were more species in the past).
I’m kind of abandoning the idea of direct proxies in this case. Camels are being used as a combined proxy for multiple genera that have occupied the continent at various times, with the understanding that its ecological role will be similar but perhaps not directly analogous to these groups. Both guanacos and vicunas are the descendants of Hemiauchenia, but are smaller and, especially in the case of the vicuna, probably differing in their exact dietary choices. The idea here is more about returning the family and its remaining wild representatives to a continent where they were previously prevalent and ecologically important, with the hope that they will create their own unique dynamic with the ecosystem that is similar but not identical to that displayed by their extinct relatives. 
That being said, Camelus ferus and Lama guanicoe would probably be functionally and aesthetically very similar to Camelops hesternus and Hemiauchenia macrocephala respectively. The western camel is often depicted in palaeoart as Dromedary-like in its appearance, but this is likely an incorrect representation. Dromedaries are very derived and have adapted for hot, tropical deserts, an ecosystem not familiar to its ancestors, which were inhabitants mostly of temperate steppes and semi-deserts, such as those occupied by Bactrians. Consequently western camels may have had similar adaptations to these habitats, such as long winter coats. Dromedaries also have only one hump, which has been shown to be a derived trait, with foetal Dromedaries developing and then losing their second hump in the womb, and adult males occasionally displaying a vestigial hump above their shoulders. This has been taken as evidence that one-humped camels evolved from two-humped ones, and that having two humps is consequently the more primitive state. This would mean that if North American Camelines had humps at all, and their spines suggest they did, it would be far more parsimonious for them to have two humps, rather than one. Large-headed llamas (Hemiauchenia macrocephalafor their part, probably looked a lot like tall guanacos, with slightly different skull and leg proportions.
Camelids offer a unique ecological service not common amongst the remaining large mammals. Their extreme lack of selectiveness when browsing allows them to be effective controls and distributors of numerous plant species that other herbivores won’t even touch. Dromedaries employed by the US army in the American southwest during the nineteenth century were observed to eat creosote (Larrea) and mesquite (Prosopis), and camels in this same area are sometimes used to control these species along with cactus (Opuntia), saltbush (Atriplex), and others. Camels and llamas will eat the thorniest, driest, toughest plants around, opening up space for other plants more useful to other herbivores and creating more mosaic ecosystems. After these species are introduced, we might begin see a dynamic develop between Camelids, Equids, and ruminants, where camels and llamas enter overgrown areas first to clear out all the scrubs and brush, and are then followed by horses and onagers to eat all of the taller, tougher grasses that pop up, to then be followed by bison and elk to eat the shorter, more nutritious grasses that grow up when all the other plants have been eaten and trampled. This dynamic would become more complex with the addition of other native and introduced herbivores, and is of course a simplification of how the real process might work, but would nevertheless potentially create some very high biodiversity in comparatively small areas.
There are also just the generic benefits that could possibly be obtained from the introduction of any sort of megafauna to the continent, namely ecotourism, sustainable offtake, and all of the numerous ecological and economic benefits I’ve covered in previous articles.  As large and charismatic animals, with unique appearances and behaviours, camels and llamas should be a huge draw for ecotourism in a rewilded American prairie. Much like the Equids discussed in the last article, camelids would represent the return of a taxon which owes its origins and most of its evolutionary history to the North American continent. I subscribe to the theory that their extinction, and that of numerous others, was ultimately anthropogenic, and it is my belief that filling some of these vacant niches through translocation is one of our greatest potential strategies against the ongoing loss of global biodiversity. North America may potentially have one of the highest diversities of large herbivores in the world someday, with representatives from as many as eight different families having an ecological claim to the continent.

Saturday 6 July 2019

Taxon Surrogate Profiles North America # 1: Equidae


            Hey everyone. I’ve hit a bit of a writer’s block with the European series, so I’ve decided to start the next one and come back to it later. The next five articles are going to be explorations of the rewilding potential for five taxonomic families that have been completely (or partially in one case) extirpated from temperate North America. These are, in order of discussion, the Equidae, Camelidae, Tayassuidae, Tapiridae, and Elephantidae. For today’s article we will be starting with the Equidae, a family which owes its origins and much of its evolutionary history to North America, and yet is no longer found there in a truly wild state, having been extirpated sometime during or after the Pleistocene-Holocene transition. I will discuss the taxonomic identity of the mid-late Pleistocene  equids of North America, and the reintroduction possibilities for this group.
            The taxonomic history of the North American horses has been long and complex. It has been repeatedly confused by the presence of feral European animals, repeated prehistoric migration between North America and Eurasia, and the tendency of palaeontologists to radically overclassify. In the past few decades. We’ve gone from having dozens of recognized native North American equids, with taxonomic affinities variously ascribed to horses, asses, and zebras, to having only two legitimate species, one of which is still very much with us. Basically all fossil equids from the mid-late Pleistocene of North America can be placed into two groups. The first is the caballine group, which is now known to be of the same species as the living Equus caballus, which includes many extant and extinct groups of animals from Eurasia, including the modern domestic horse (which descends from the extinct European wild horse or tarpan) and the wild Przewalski’s horse, or takhi, from Asia. The second group is the stilt-legged equids, which were originally thought to be members of the living Asinus (sub)genus, which includes the Eurasian and African wild asses (Asinus hemionus and Asinus asinus), as well as the domestic African ass, or donkey. This conclusion was arrived at through morphological analysis, but genetic studies have since shown that this group is distinct and deserves its own genus. Consequently all stilt-legged equids from the mid-late Pleistocene of North America are referred to as variations of the single species Harringtonhippus francisci. With this information we can now refer any equid remains from this time period to one of these two groups.
            The caballines have been, in a sense, already reintroduced. Areas of North America once occupied by various extinct subspecies or varieties of Equus caballus (ex. complicatus, conversidens, niobrarensis, lambei, occidentalis, scotti, etc) were very quickly recolonized by feral Spanish horses, Equus caballus caballus, after said horses were brought to North America by the conquistadors. These populations resulted in the modern mustang, which was quite happily able to recolonize its former range through a combination of natural migrations and trading by First Nations peoples. These days however, mustangs are quite rare, and have been severely reduced in number and frequently crossed with other breeds. Some herds have purposely had individuals with certain colourations removed in order to create a more “primitive” appearance in the remaining herds, leading some to assert that the animals have always looked this way and that their primitive markings are the result of natural selection, when in reality the breed remains quite domestic and can easily be brought back into captivity. Knowing this, and considering their reduced population, I think other options could be explored when selecting horses for an experimental rewilding site. Considering their truly wild status (which has been unsuccessfully challenged in recent years), their truly primitive appearance and behaviour, and their adaptations to (semi-)arid steppes and semi-deserts, which represent much of the available habitat in central North America, I believe the Asiatic wild horse (Equus caballus przewalski) would be an excellent choice for introduction to North American rewilding areas. Having made a considerable recovery from their near-extinction in the first half of the twentieth century, there exists a sizeable captive population in North America which could be used to establish a free-living breeding population on the Great Plains or adjacent habitats.
This would run contrary to my suggestions for rewilding domestic horses or crossbreeds in Europe. This is for two reasons: the first being that domestic horses are more closely related to the European wild horse (Equus caballus ferus) than is the Asiatic wild horse, and the second being that most of the available habitat in Europe is different from what takhis are adapted to, and more easily occupied by native horses which have developed appropriate ecotypes. Genetic evidence suggests that the two living horse subspecies are about equally related to Equus caballus lambei/lenensis, which occupied the Bering strait, and are consequently likely to be equally related to the other North American horse subspecies, since Beringia would have represented the migration corridor between Eurasia and North America. Knowing this, it seems more appropriate to select the taxon that is already considered wild, could use the conservation support, and will not require any significant selection. The fact that takhis already look like primitive wild animals will also be useful for rewilding projects funded by ecotourism. Their ability to occupy non-steppic habitats is established from their introduction to conservation areas in Europe with varying levels of forest cover. Probably the best course of action is to begin with the central plains, where most American rewilding projects are focused/planned anyway, and work outwards from there. Their ability to thrive in colder climates, such as those that might be experienced in rewilding areas in the far north, will need to be assessed. However, considering we now have the whole genome of an extinct relative adapted to these areas, genetic hybridization might be an angle. Hybridization with existing domestic breeds adapted to these areas, such as the Yakut pony, would certainly be easier, but it would also potentially introduce some less desirable behavioural traits. The best course of action will be decided when relevant.
As to the replacement for Harringtonhippus, the substitute used will be a generic proxy, rather than a subspecific one. Based on morphological and chromosomal differences, I think it appropriate that the various Equus subgenera be elevated to genus level, including Asinus, the group that includes the wild asses. Although not actually a member of this group, the North American stilt legged equids shared some remarkable morphological similarities with Old-World stilt-legged horses surviving today, and seem to have occupied similar open and arid habitats based on fossil records. Knowing this, I think the best proxies would be various subspecies of Asinus hemionus, the Eurasian wild ass, which were once widespread across multiple habitat types in Europe and Asia. While the kulan and onager subspecies have been proposed for redistribution in Europe and western Asia, and the khur subspecies is in the process of being reintroduced to new sites in India, the Mongolian hemionus subspecies and the Tibetan kiang subspecies might potentially be used in North American rewilding projects, with the former being well suited to the prairies and deserts of northern Mexico, the central/western United States, and southern Canada, and the latter being adapted to colder habitats such as those found in northern Canada and Alaska. These two subspecies are the most populous of any of the Eurasian wild ass varieties, with almost 70,000 of the kiang subspecies remaining in the wild, and almost 20,000 of the hemionus subspecies. Oddly enough however, they are also the least studied taxa, and the rarest in captivity. Consequently, individuals used in rewilding projects in North America would probably have to be wild-caught, which would be advantageous for acclimatization purposes, but expensive due to the capture and transportation costs.
There are many potential benefits to equid reintroduction in North America. Horses are an important part of the grazing regime in any ecosystem where they occur. Their ability to eat tougher and poorer quality forage allows them to open up habitats for more selective herbivores. Feral mustangs were often followed by herds of bison for this exact reason, in a dynamic mirroring that of zebras and wildebeest in Africa. Something worth considering however is that predation by wolves and pumas would likely be insufficient for population control and human intervention would possibly be necessary to keep numbers in check. The main predator of the horse in the Pleistocene was the American lion (Panthera (leo) atrox). North America probably has a better chance of returning lions to its ecosystems, at least in fenced game reserves, than does Europe, and I for one would be very excited to see that particular predator-prey relationship first-hand. A truly rewilded Great Plains could potentially become one of the greatest ecotourism destinations on Earth.

Island Rewilding Series #1: Reunion Island

            The most common usage of purposeful taxon substitution in non-hypothetical situations thus far has been for the purpose of cons...