All the World's Antelopes: Gemsbok and Oryx

Gemsbok

As I have discussed previously, there is no such thing as an antelope, in the strict scientific sense. That is to say, they do not form a natural group of organisms, being defined only as those members of the cattle family that aren't sheep, goats, or obviously cow-like. This covers a wide range of animals, some closely related, but others much less so.

I've previously looked at the various species of gazelle, and at the spiral-horned antelopes (which are actually "bovines"). Now it's time to look at the others.

Linnaeus' original catalogue of scientific names, published in 1758, included five species that we would now call antelopes. In that catalogue, they are listed as goats, based primarily on the shape of their horns, and therefore sit alongside the chamois and ibex. Two of these, the dorcas gazelle and the blackbuck, are now placed within the gazelle subfamily, while two others are relatively small "dwarf antelopes", which I will cover later.

Hedgehogs versus Killer Robots

Hearing is a key sense for just about any mammal species. While humans, and primates in general, place particular importance on vision, this isn't true for many other mammals. Granted, that's usually because of the significance of scent, which we humans are particularly bad at, but hearing can hardly be discounted, even for us. 

The range of hearing, however, varies dramatically between different species. For humans, the typical range is from about 20 to 20,000 Hertz, which covers about 10 octaves (middle C is 261 Hz) although the upper range drops off with age, and there is some leeway under perfect conditions. Many mammals can hear outside this range, with smaller animals, in particular, being able to hear higher notes. This can be of more than academic interest, since it means that the soundscape a particular animal lives in may not be the same as our own, and that can have a bearing on conservation - we might think somewhere is quiet and peaceful, but other species might not agree.

Hungry Hippos

The hippopotamus (Hippopotamus amphibius) is an unusually large animal. Among land-dwelling mammals, only the elephants and some species of rhinoceros are larger. It is also, like elephants and rhinos, herbivorous and, since it prefers to eat plants that aren't especially nutritious, this means it needs to eat a lot. 

As in, it eats 35 to 50 kg (77 to 110 lbs) of food each day. 

Which is fine if the hippo happens to be out in the wild, far from human interference. But the reality is that there are fewer and fewer such places around these days. It's not so much the urban sprawl that humans bring, or even the roads and other infrastructure of an expanding African economy, but more the cropland that's required to feed us all. Although hippos are hunted for the ivory in their teeth, the number one threat to their survival is probably the expansion of farmland. Compared with many other animals, this is exacerbated by their reliance on large amounts of fresh water, so even if the farmland isn't near them, they suffer if water is diverted to where it is needed for crops. 

Gorilla Communities

It is, I would hope, well-known that the closest living genus to our own is that of the chimpanzees and bonobos. The second-closest is, of course, that of the gorillas. There are two species of gorilla, each with two subspecies, and both are considered "critically endangered" - literally on the verge of extinction. For one species, this is, as one would expect, largely due to their tiny surviving population and restricted range. 

There are many factors that we need to consider when attempting to reverse this, and some of them also have a bearing on the evolution of our own species. Among these is the question of how gorilla groups are socially constructed and how they interact. It turns out that here, we can't just consider "gorillas" en masse because the two species behave in very different ways. For example, while one species can have multiple silverback males in the same troop, this is rare (but not unheard of) in the other.

Wolves, Foxes, and Food

Large scary predators are, by their nature, rare. There simply can't be too many of them, or they would run out of food to eat, something typified by the trophic pyramid often seen in biology textbooks: plants are eaten by herbivores are eaten by carnivores are eaten by bigger carnivores, with each step necessarily having a smaller total mass. The reality is, of course, somewhat more complex than this simple chain would suggest, most obviously because it ignores omnivores and decomposition.

But the basic idea holds, and apex predators - those that are large enough that nothing else normally eats them - exist in much smaller numbers than herbivores or smaller carnivores. This means that, relative to their numbers, they have a disproportionate effect on the ecosystem within which they live. Take away the apex predators and, even though there weren't very many of them to begin with, you will radically change the local ecology.

And, because they are relatively few in number, apex predators tend to be especially vulnerable to being wiped out. That's even assuming that humans don't focus on them deliberately out of fear, whether for their own lives or for the good of their livestock. Globally, apex predators are declining. (On this blog, we're mostly interested in mammals, but consider, for example, that at least eight of the 23 species of crocodile/alligator are currently thought to be endangered).

Wild Mammals of London

Arguably the single biggest threat to the continued survival of animal and plant species is loss of habitat. Even if an animal isn't actively hunted, the ever-growing human population means that there are simply fewer suitable places for them to live. Logging and the expansion of agriculture are probably the biggest factors here, at least in terms of the area affected, but it's hard to argue that the recent growth of urban sprawl isn't another.

The urban environment is obviously a difficult or impossible one for most wild mammals to exploit. House mice and rats are an obvious exception, and there are also domesticated pets, but for truly wild creatures it's a different matter. While it may no longer have (say) bison or wolves, upstate New York is still home to seven species of shrew, three moles, four hares or rabbits, 22 different kinds of rodent, ten bats, nine mustelids, two foxes, and three deer, plus coyotes, bobcats, raccoons, striped skunks, and black bears. Manhattan... not so much.

A Tiger's Dinner

One of the basic concepts in ecology is that of the food chain; the idea that plants are eaten by herbivores are eaten by small carnivores are eaten by large carnivores. The reality is both more complex - because, for example, omnivores exist - and simpler, because, at least on land, many of the largest carnivores eat large herbivores, not smaller carnivores. Nonetheless, there's still an underlying truth, and it introduces us to concepts such as the apex predator.

An apex predator is essentially a carnivore that has no predators of its own, an animal that sits at the top of its local food chain. Many mammals fit this description, including wolves, big cats, bears, and killer whales. (The last of those, of course, being an example of a large carnivore that does mainly eat smaller carnivores). Outside the world of mammals, one could add eagles, crocodiles, and sharks, among others. Humans could count as another example, given that we obviously don't have regular predators, but this does depend on your exact definition, since we're clearly omnivorous and, in many parts of the world have a nearly or totally herbivorous diet.

Return of the Rabbits?

This one is wearing a radio collar...

It's abundantly clear that humans have had a dramatic effect on the number and distribution of animals across the globe. (For that matter, by some measures, plants may be doing even worse). There are great swathes of the world where particular animals were once common but are not so any more. Just to take a dramatic and obvious example, Great Britain used to be home to wolves and bears but we don't see those around any more. Those are, of course, widespread elsewhere, but other animals may be less lucky.

In some places, however, a key method in conservation may be reintroduction, bringing animals back to their native habitat, either from elsewhere, or directly from captive populations. This can help restore natural ecosystems, with the return of one originally native species helping others that are now in decline, but have yet to disappear altogether. Again taking Britain as an example, there are currently efforts underway to reintroduce beavers to the country, where they have been locally extinct since the 16th century. Similar programs for other animals exist elsewhere, but the reality is that such efforts are not always successful.

We're Up All Day to Get Lucky

One of the key characteristics that's often listed for the behaviour of a mammal species is what time of day it tends to be active. There are four basic options here, of which the most obvious are diurnality and nocturnality. The others are crepuscularity if it's most active around dawn and dusk but not in between, and cathemerality if it really doesn't care - often because it lives underground. But, either way, it's natural to assume that this behaviour is relatively fixed in an animal; either it's nocturnal or it isn't.

In reality, however, it turns out that this can have a lot to do with the circumstances. And, in the modern world, those circumstances are most likely to be shaped by... what else, but humans? 

The issue, of course, is that humans are for the most part diurnal. Which isn't much of a problem for animals that are naturally nocturnal, but can be if they, too, would prefer to be active during the daylight hours. What we see time and time again across the world, and across different mammal species, is that where humans are most likely to encounter wild animals, those animals shift their behaviour towards nocturnality to avoid the stress of meeting us too often.

When the Desert is Too Dry

The round-tailed ground squirrel lives
further east, and is not threatened

Many mammal species are territorial, carving out a patch of land for themselves which they then defend from same-sex members of their own species. Typically, they are less bothered about members of the opposite sex, for obvious reasons, and such territories will often overlap. Male territories tend to be larger than those defended by females, making it easier for them to meet as many females as possible. 

The size and relative location of such territories naturally vary between species, but also depend on the local conditions of terrain, climate and so on. The harder it is to find food, for instance, the larger your territory will need to be. As young animals grow up and leave home, they will need to find unoccupied territories to inhabit, or else somehow drive an existing resident out and take over. Males commonly travel further than females so that they don't end up with only their sisters or close cousins as potential mating partners, although there are a few species where it works the opposite way around.

Cheetahs and Wild Sheep

The cheetah (Acinonyx jubatus) is surely one of the most familiar of African animals, due in large part to their prominence in wildlife documentaries such as Cheetah Family & Me. They are charismatic, distinctive, and not especially rare or difficult to find. Unlike, say, tigers, they are not internationally listed as an endangered species, although their population has declined rapidly enough over the last few decades that they do qualify for the lesser rating of "threatened" or "vulnerable" species. 

This does, however, disguise some significant regional variation.

How we should divide the cheetah into subspecies is not absolutely clear. From at least the 1970s, five subspecies were recognised, Two of those were merged in 2017, on the grounds that the East African form could not be reliably separated from its southern relative genetically. Even then, cheetahs have so little genetic variation across their range - due to an apparent population bottleneck when they almost died out at the end of the Last Ice Age - that support for the existence of two of the other subspecies remains a little shaky. Still, four subspecies is, for the time being, the general consensus.

Fruit Bats of Madagascar

While most attention tends to focus on large charismatic animals such as rhinos and tigers, it will probably come as no surprise to discover that many species of bat are endangered. Here in Britain, all bats are legally protected by the Wildlife and Countryside Act 1981, making it an offence to disturb their roots. That's perhaps an unusually robust example, but other protections and conservation efforts exist across the world.

On the other hand, it is true that the majority of bat species are not especially threatened, at least on a worldwide scale - although things may be different locally. Bearing in mind that around one in six bat species are so recently identified and so little studied that we simply don't know how common they are, only around another one in six are rare enough to be listed as "threatened" by the International Union for the Conservation of Nature. Still, that's not exactly a small proportion, and since there are somewhere around 1,400 named species of bat, it's not small in absolute terms, either.

Tha bats are a highly diverse group, representing no fewer than 21 taxonomic families, none of which are likely as familiar to the layman as terms such as "cat family" or "deer family". Some of these contain very few species, representing oddities that don't quite fit into any of the main subgroups, but there are still five families with over a hundred species each. Of these, the one that contains the highest proportion of threatened species is the fruit bat or "flying fox" family, the Pteropodidae.

Benefits of a Deadly Predator

A basic concept in ecology is that of the trophic level, a concept that lines up life forms by where they sit in the food chain. Plants are at the bottom level, taking energy directly from the sun, then the next level up are the herbivores, which eat the plants. Above that we have primary predators eating the herbivores, and then secondary predators eating the primary ones. Because the transfer of energy is never perfect, each level will be smaller than the one below it, with fewer individual life forms in it, thus forming a pyramidal pattern.

The reality is more complex than this. Secondary predators also eat herbivores, omnivores are common, really large herbivores aren't likely to be eaten by anything, there may be more than two steps in the chain of carnivores, and we can't forget the detritivores and fungi. And so on. So what we actually have is a "trophic web", a complicated set of interactions where some animals don't fit neatly into a single level on the pyramid. Nonetheless, that doesn't make the basic idea useless and one of the concepts it leads to is the apex predator - the large carnivores that have no predators of their own (at least as adults).

Dunnarts in the Sandhills

It's a recurring theme of this blog, especially notable in last year's series on Old World leaf monkeys, that a great many mammalian species are threatened in some way. Population numbers of many species are declining, to the point that their continued existence is in doubt, often due to human encroachment on their habitat, but also due to the habitat itself changing as climate change continues. In this context, the quest of zoologists to understand how mammals (and other animals) behave is not just one of intellectual curiosity but can be of direct benefit to the creatures themselves.

For example, it is useful to conservation efforts to understand not only where a given species lives, and the habitat requirements it may have, but how it makes use of that environment. (Obviously, there's more to it than this, for example, how different species in the same area interact with one another but we'll stick with this one point for today). What particular features of the habitat are important to it? How much land does it need? How is its population distributed across the area? 

Decline of the Woodrats

The wild mice and rats of the Americas are not members of the true "mouse family", the Muridae, but instead belong to the Cricetidae, a name which translates as "hamster family". The vast majority of species in the family are not, however, hamsters, since the group includes both the voles (of which there are many) and the aforementioned New World mice and rats. Many of these latter are found in South America, with plenty more in Mexico and Central America. Most of them are mouse-sized, an example of the great success of the mouse body-plan where, despite having diverged from the true mice over 30 million years ago, such creatures as the American deer-mice differ from the house mouse by, at best, having a different colour pattern.

Just as some members of the mouse family developed larger size, evolving into such things as the familiar sewer rat (which, of course, has been introduced to America, even though it's not native there) so to did some of their New World counterparts. In the southern US, three different lineages of such creatures can be found: the muskrat (which is actually a giant vole), the cotton rats (which are related to the vast collection of South American rats and mice), and a third group variously called pack rats or woodrats.

Spotting Ocelots

There are a number of different species of cat living in South America, including some that are not widely known by the general public. Across much of the continent, however, the most abundant are often the ocelots (Leopardus pardalis), outnumbering both the larger cats that require substantial food resources and the smaller, more localised ones. Aside from the desert regions west of the Andes, ocelots live across almost the whole of the continent from northern Argentina to the Caribbean coast and their population is large enough that they are not generally considered a threatened species.

But that broader picture, which is generally positive for the species, hides some local variation. They are not, for example, especially common in the Caatinga, the area of dry scrubland that covers the easternmost regions of Brazil. More significantly, perhaps, they also become less progressively common once you leave South America and head north. Ocelots are found throughout Central America, and along both coastal regions of Mexico, and they are even found in small numbers in southern Texas and Arizona. In both of these latter countries, however, their populations are low enough that they are listed as endangered species by the local authorities responsible for such matters - the US Fish and Wildlife Service and the Secretariat of Environment and Natural Resources.

Bats in the Megafire

A little over ten years ago, I wrote on this blog about the effect of forest fires on bats in Florida. It turned out that the bats in question, which were big brown bats (Eptesicus fuscus), one of the most common bat species in the US, were actually quite happy when forest fires tore through the sandhills where they lived. This is because it improved their environment, in particular making it easier to fly about through what might otherwise be a mass of tangled vegetation and thick undergrowth. 

That was a decade ago, and further studies since that date have broadly confirmed the findings of the one I was referring to in that post. A 2019 study, for example, showed that the same was true for a number of species in Australia. Overall, it seems that, at worst, forest fires have no overall effect on bat populations and, in general, they're actually a benefit.

Mouse Lemurs in the Mangroves

Well over 6,000 species of mammal have currently been described, many of which have only been confirmed as distinct species in the last few decades. There is undeniably a trend in the 21st century towards "splitting" of species along comparatively fine dividing lines, but it's also the case that this has been supported by advances in genetics and the like that have made it easier to tell when two groups of animals really are different, and not interbreeding.

But the corollary to this is that many of these species look extremely similar. It's often the case that, once a new species has been described on the basis of genetics, we can point to physical differences between it and whichever species we split it off from. But these are necessarily minor differences, perhaps previously thought sufficient to justify a designation as a subspecies, but more likely not noticed at all. Given the physical similarities, we'd expect that their diet, behaviour, and so on would also be similar - they are, after all, very close relatives.

Stopping the Water Vole Killer

I have often referred on this blog to the number of mammal species that are currently faced with extinction, of being wiped totally from the face of the Earth. Depending on how strictly you want to define the threat, this could be anything up to 25% of the total known species, although it's worth noting that a great many other species have declining populations, if not ones that are likely to vanish altogether any time soon.

For many species, even if extinction is not a threat, extirpation can be. This is, essentially, a local extinction, where the species dies off entirely in some particular area, but still survives somewhere else. While it can be any area you like, in conservation terms, we tend to be talking about either countries or reasonably sized islands. Or, as is the case in Britain, both.

Many species of mammal have been extirpated from the British Isles over the course of our history. Wolves are one of the more famous examples here, with the last official record of a dead wolf dating from 1680 in Scotland (it's unlikely to have literally been the last, and rumours continued for another hundred years or so, although it's hard to know how many of them were accurate). In a number of other cases, such as the hazel dormouse, local populations today very much seem to be in decline.

Grey Seals on the Rebound

According to the IUCN Red List, which is probably the most widely used catalogue of conservation statuses, roughly a quarter of all mammal species are "threatened with extinction". That's a broader category than "endangered species", but, either way, it's a proportion that's growing. (As it is, of course for non-mammalian species; amphibians, for instance, seem to be doing particularly badly).

Partly that's because we're getting better at evaluating such things, and identifying species as being at risk when we previously knew little about them - or, in many cases, didn't even know they were separate species. But it's also a consequence of mankind's ever-expanding ecological footprint, as some species become threatened that weren't previously.