American wildlife ecologist Craig Downer says wild horses and donkeys can make valuable contributions to Australian ecosystems in many different ways. He described them in this poster presentation at the Ecological Society of Australia annual conference in 2014.
Wild horses can complement an ecosystem, or life community, in many direct and obvious as well as more subtle ways. This they do when permitted their natural freedom to move and interrelate over a sufficiently extensive intact habitat and time period.
Dietary benefits, buildings, dispersing viable seeds
Equids possess a caecal, or post-gastric, digestive system. This enables them to take advantage of coarser, drier vegetation and, through symbiotic microbial activity, to break down cellulose cell walls to derive sufficient nutrients from the inner cell without overtaxing their metabolism. In drier regions, this can give equids a distinct advantage.
Consumption by equids of coarser, drier vegetation can greatly benefit sympatric, pre-gastric (ruminant) herbivores, and energize and enrich the ecosystem as a whole. By recycling chiefly the coarse, dry grasses as well as other dry, withered herbs, forbs and bush foliage, the horses and burros expose the seedlings of many diverse species to more sun, water and air, thus permitting them to flourish. The latter can then be consumed by ruminants (see R.H.V. Bell 1970).
Of great importance is the contribution by wild equids of significant quantities of partially degraded vegetation in the form of feces deposited on the land. These droppings provide fodder for myriad soil microorganisms; the resulting fecal decomposition builds the humus component of soils, lending ecologically valuable texture and cohesiveness. As feces slowly decompose, they gradually release their nutrients over all seasons and, thus, feed the fungal garden that exists in soils, thereby increasing the soil’s absorption of water – that vital limiting factor in semi-arid and arid regions.
Equid feces lend more sustenance to decomposers and food webs that involve mutually sustaining exchanges among all classes of organisms. The latter include many diverse insects, birds, rodents, reptiles, etc. This could help bolster many native species in Australia.
The less degraded feces of equids contain many more seeds that are intact and capable of germination and from many more types/species of plants when compared with ruminant grazers. Thus, the horses’ wide-ranging lifestyles can greatly assist many plants, including Australian natives, in dispersing far and wide and, so, in filling their respective ecological niches. This enriches the food web and allows a greater diversity of animal species, including Australian natives.
Horses aid myriad plant and animal species by their physical actions. As an example, breaking of ice with their hooves during winter freezes allows other animals to access forage and water. Many of these would otherwise perish. Similarly, they open trails in heavy snow or through heavy brush, allowing smaller animals to move about in search of food, water, mineral salts, shelter, warmer areas, mates, etc.
A little-recognized fact is that the wallowing habit of wild equids creates natural ponds whose impacted surfaces become catchments for scant precipitation or summer cloudbursts. These provide a longer-lasting source of water for a wide diversity of plants and animals. This can even help to create an intermittent riparian habitat for desert amphibians and many other desert species including those of the Australian Outback. Ephemeral plants that quickly flower and set seed, including many composites, are benefited from these catchments – especially valuable in regions with clayey soils.
Wild horses also locate water seeps through their keen sense of smell and enlarge these through pawing during critical dry periods of the year, even digging down to the sources at rocky fissures. This allows many other species to access water, species whose individual members would otherwise perish. For these and many other reasons, wild equids should be treated as keystone species that contribute positively in a variety of ecological settings.
Role as prey
Wild horses are natural prey of certain carnivores and omnivores including in Australia dingoes, crocodiles, and wild dog packs.
Suitability to arid and semi-arid ecosystems
Wild horses and donkeys are well suited to life in arid and semi-arid ecosystems. One reason is obvious: their great mobility. With their long limbs and sturdy, single-unit (soliped) hooves, they are made for movement. In such semi-arid or arid regions, this extensive movement is vital for survival. In order to obtain enough forage, a wild horse must often roam over several square miles each day, selecting appropriate plants to prune; reaching a water hole may involve traveling over a hundred-mile round trip in a grazing circuit of two or three days. Wild horses do not camp on riparian habitats as do cattle.
During very hot, dry spells, a wild horse band must stay close to water, tanking up every day with about 10 to 12 gallons for a mature horse. A spring can be shared by several bands. These form an orderly hierarchy for watering should more than one band arrive at a source at the same time, often late in the day. When melting snow or fresh cloudbursts paint the land with ephemeral water sources, wild horses can disperse into areas further away from perennial lakes and streams and to these ephemeral sources. Here they employ their keen sense of smell in detecting even very small and hidden water sources. They can also negotiate rougher, steeper, and rockier terrain than domestic cattle, and prevent flammable vegetation from building up there.
Through a hammer-like hoof action upon the ground, wild equids aid vegetation by pushing seeds firmly into the soil where they may successfully germinate. Their feces also provide a fertile bed for the germination of seeds.
Equids’ post-gastric digestive system in relation to global warming
The horse’s post-gastric digestive system does not emit as much gas as is the case with pre-gastric ruminant grazers, and permits them to greatly reduce dry, fire-prone vegetation over vast areas without overtaxing their metabolism. Thus, they help to prevent catastrophic fires that global warming, or more to the point, human civilization’s pollution of the atmosphere, is causing.
By drying out vegetation and provoking catastrophic fires – rampant in western and southern North America, Australia, and much of the world – the catch-all “global climate change” threatens planetary life as we know it. This will especially be the case if global ocean currents stop circulating because of glacial and ice cap melting, etc. Wild equids can greatly help to save the day if allowed to play their own special role in reducing flammable vegetation, in building soils, in seed dispersal, in preventing catastrophic, soil-sterilizing fires, etc. They stand ready to counter imbalances brought on by human civilization and its contamination of the atmosphere, much of which is caused by hordes of domestic livestock (de Haan et al. 2006).
Humus and soil building
Equid feces build the humus content of soils to a substantial degree. This humus allows soil to gain more texture and retain more water, which dampens out fires; humus promotes more productive and bio-diverse plant and animal communities. Because their feces are not as thoroughly degraded in the gut as those of ruminant grazers, they contribute more to food chains/webs, e.g., dung beetles to birds and lizards to higher trophic predators such as cats and eagles, etc.
Equine feces aid the watershed by creating damper conditions, because the soil particles to which they reduce (micelles) retain more moisture, i.e., more water adheres to the surface area of these particles. Hence ground water tables are replenished, feeding more seeps and springs more continuously. And upon these springs and seeps, many species of plants and animals depend. Some fire is of benefit to an ecosystem, but fires that over-consume, over-extend, and over-intensify can set the evolution of a terrestrial life community way back and result in a very sterile environment that could take thousands of years of “peace” to recover.
Upper incisors and further insights
Equids possess both upper and lower incisors that permit them to selectively nip pieces of vegetation, such as grass or the leaves of bushes or trees. Major ruminant grazers such as cattle and sheep do not have upper incisors and consequently can and do rip up plants by their roots more frequently with the action of their lower teeth and tongue against their hard upper palates. This often exposes soils to destructive wind and rain erosion, especially when too many of the ruminants are placed upon any given area of land. And wild horses are much more mobile in their daily and seasonal feeding rounds than are cattle.
Equids’ relationship to biodiversity
Equid species diversify and strengthen the community they inhabit in a variety of ways when allowed to achieve population stability over time and when not over-imposed upon by humanity. The process of natural selection must be allowed to operate sufficiently long for this to be the case. Then these equids can and do create a greater variety of environmental conditions that make possible a greater variety of niches that can be occupied by the species that are coevolving with them.
Being large, powerful animals, equids can push their way through thickets of brush to form trails. Specifically, they open thick vegetative understories to light and air, and the more diverse exposures resulting from equine activities create conditions intermediary to the extremes of wind, temperature, and various soil conditions. This physically defines a greater variety of niches fillable by a more diverse array of species.
Equids’ relationshop to vegetative productivity and natural cycles
When allowed to integrate into wilderness, the individual life histories of wild equids come to reflect natural oscillations, such as annual seasons and more long-term cycles. This they do along with the plants and animals that share their habitat. They harmoniously blend over time. As large animals that eat relatively large quantities and disperse their grazing and browsing activity over broad areas as semi-nomads, equids can become the harvesters and the renewers over vast ecosystems, true to their keystone role.
Their cropping of vegetation, often dry and coarse, reduces the possibility for major, soil-sterilizing fires. This cropping sparks vegetative renewal, the re-budding of new and tender shoots of greater nutritional value, especially to ruminants whose digestive and metabolic systems are over-taxed by the coarse, dry vegetation that equids can better handle. And thus the overall productivity of the land is annually increased, as studies prove (Fahnestock, JT and Detling, JK. 1999 [both]).
Natural self-stabilization of population and reserve design
Wild horses form tight-knit stallion and elder-mare-governed bands. Over time, each band searches out and establishes its own home range, which may cover hundreds of square miles annually in drier regions. The ecological mosaic that results among all such particular band home ranges in a given area prevents over-crowding and overgrazing. Once available habitat is filled, the horse, as a climax species, limits its own population as density-dependent controls are triggered.
In the immediate future, true wild-equid-containing sanctuaries need to be established. Here livestock should be excluded or at least greatly minimized and wild equids allowed to establish viable populations in the thousands of individuals (Duncan 1992). These fairly populated sanctuaries will be viable in the long-term. They will preserve the vigor of the horses and burros they were designed to conserve.
Employing principles of Reserve Design, the following directives will serve as guides in achieving the above goals:
- Allow each wild equid herd to fully fill its ecological niche space within each given area bounded by natural or where necessary artificial barriers, and by buffer zones. Then allow each specific herd to self-stabilize, or auto-regulate, its population, within this area. Such auto-regulation can happen if we humans allow. Equids are “climax species,” which is to say, members of the “climax successional sere,” or stage, and do not expand out of control to destroy their habitat and ultimately themselves. Each band within a herd population is usually governed by a lead stallion (patron). He watches out for and defends the band and does most of the breeding. A usually older, lead mare also aids in this role. This mare is very wise as to where the best foraging, watering, mineral procurement, sheltering areas, etc., are located. She leads the band along paths uniting these habitat components. These include longer seasonal migratory routes between higher summering and lower wintering habitats. Both patron and lead mare socially inhibit reproduction among younger members of their band. As resources become limiting, physiological and social responses result in decreased reproduction in any given band or herd (Rogovin and Moshkin 2007).
- Employ natural barriers where possible, or, where such do not exist, semi-permeable, artificial barriers, where necessary, in designing each wild horse sanctuary.
- Design and employ buffer zones around the wild horse sanctuaries. Here a gradual tapering off of wild horse presence would occur through the implementation of discouragements to their transiting into areas where danger exists for them, such as in farms or cities. This may involve the use of what wildlife managers term “adverse conditioning” as well as “positive reinforcement”.
- In order to realize healthy, balanced wild-horse-containing ecosystems, as full a complement of plant and animal species should be allowed. Wherever possible, this should include large carnivores/omnivores native to the region in question, such as the dingo. These will provide an additional limitation on wild horse populations (and wild donkey), one that will act through natural selection to make any given population more fit for survival in the wild and more harmoniously adapted to its particular ecosystem.
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