Black Bears and the Uncertain Apex

The concept of the food pyramid is a central one in ecology. The idea is that since consumption cannot ever be 100% efficient, every type of animal must necessarily be less common than whatever it is that it feed on, at least in terms of its total biomass. Plants are more common than herbivores are more common than small carnivores are more common than larger carnivores.

The actual picture is more complicated than this. Many "carnivores" are at least partly omnivorous, and they often eat large herbivores more regularly than they eat small carnivores. Plus, we also need to consider the detritivores and parasites. But the general pattern holds, and at the top of the pyramid, we find the apex predators. 

It's possible to argue as to what exactly constitutes an apex predator. The general idea, however, is that they feed on other animals without being preyed upon themselves. At least among terrestrial mammals, an average body mass of more than about 15 kg (33 lbs) is generally about enough that predators need to manage their own population (through competition, territoriality, infanticide, etc.) rather than having to worry about something larger and scarier managing it for them. 

Naked Aggression

Evolutionarily speaking, it is in the interests of animals to have as many offspring as they can, so long as those offspring will themselves reach reproductive age. However the means for a male to do this may be different from those best employed by females. This is especially true in mammals, because the female has to put considerable resource into pregnancy, lactation, and general care of the young until they are old enough to fend for themselves. The male, however, doesn't have to do any of this, and, in many species, his role in matters may be completed as soon as he's finished mating.

This leads to the concept of sexual selection, where the evolutionary demands on the male may be different than those on the female, leading to different behaviours and appearances. There are often said to be two main driving forces behind such sexual selection. The first is the need for males to compete with one another for access to females, resulting in larger, more heavily built males, often with natural weapons of some kind, such as horns or tusks. The second is driven by the females, when they choose a mate based on some particular feature, leading the males to emphasise that feature in response. (This is, perhaps, most obvious in birds).

The Hunting Grounds of Small Cats

The big cats - lions, tigers, leopards, and so on - are arguably amongst the well-known of all wild animals. They frequently figure in zoos and nature documentaries, and, from the scientific perspective, they have been the subject of numerous studies down the years. Even the medium-sized cats, such as lynxes, bobcats, and ocelots, are well known, and, at least in the case of the European and North American species, also well-studied.

We know somewhat less about the assorted species of genuinely small cat - the ones that are about the size of the typical domestic moggy. Yet there are an awful lot of them, even if most members of the public would likely have a hard time naming more than one or two.

One such example is Geoffroy's cat (Leopardus geoffroyi) named for - though not discovered by - the pioneering French naturalist Étienne Geoffroy St Hilaire. This lives in southern South America, reaching Bolivia, Paraguay, and the southern tip of Brazil in the north, and also found just over the border in Chile, but mainly inhabiting Argentina and Uruguay. While they prefer terrain with scattered trees and plenty of bushes, the also live in open grassland, and are found right down to the very southern coast of South America, although not on the islands beyond.

Rabbit v. Rabbit

Mountain cottontail

There are literally thousands of different mammal species currently recognised. Most of them are small, and a great many of them can be quite hard to tell apart at first glance. Or even second glance, quite frankly.

The reason that they look so similar is that some body plans have been particularly effective, allowing the creatures possessing them to survive and multiply across the globe. But, if they're so similar, why doesn't one species, over the course of time, drive the other to extinction? Even if one isn't even just marginally better at doing whatever it does than the other (and, since they aren't literally identical, that's unlikely) then sheer bad luck ought to hit one or the other of them eventually.

Struggle of the Marsh Antelopes

Puku

All things being equal, herbivores would prefer to live in those areas with the best and most lush vegetation. The reality, of course, is that all things are very rarely equal. There are all sorts of reasons why a herbivore might not wish to live somewhere where they can get the best quality food.

One of those reasons is the presence of predators. If predators also live where the vegetation happens to be best, a herbivore has to strike a balance between the quality of the food and the risk of getting eaten. But a herbivore also has to worry about... other herbivores.

If you eat exactly the same thing as some other animal, and try to do so in the same place, whichever one of you is even marginally better at it is going to, over a sufficiently long period of time, out-compete the other one and drive it to at least local extinction. We see this, for example, in England, where grey squirrels introduced from North America have out-competed the red squirrels native to the island. There are only a few places left in England where you can still see red squirrels, but the foreign grey squirrels are quite common.

Sharing Resources

Black-and-gold howler monkeys. The black one is male, the gold, female.

I've mentioned previously how animals have to juggle their time between different activities, such as feeding, watching for predators, and reproducing, and how that can be affected by things such as the size of the herd they live in (if any). Unsurprisingly, this works both ways, with the size of a herd being affected by the animal's lifestyle.

One of the main reasons for living in a herd is that it makes it easier to watch out for things that are going to try and eat you - you don't all have to be watching all the time, which means that each individual can spend more time eating, or doing whatever else it wants. So a herd has to be large enough for that to be worthwhile, and there may also be a minimum size on viable herds based on such things as the way the animal breeds. On the other hand, a really large herd is going to require a lot of food to sustain it, so the amount of food available is likely to put an upper limit on the herd size.

Battle of the Sabretooths

Machairodus giganteus

The cat family is divided into two living subfamilies. One group are the pantherines, or large cats, which include lions, tigers, jaguars, and the various kinds of leopard. The other are the felines (which means that, in the technical, scientific sense, lions are not felines - the correct collective term that includes all members of the cat family is "felid"). The felines are quite variable in size, from cougars and cheetahs at the high end, through a range of mid-sized cats such as lynxes and ocelots, down to wildcats and their familiar domestic relatives.

But there once used to be a third subfamily of cats, and they represent, with the possible exception of mammoths, what are probably the most widely known of all extinct mammals. In fact, I'd guess that they are the only extinct mammals that come at all close to dinosaurs in terms of popularity. I refer, of course, to the sabretooth cats.

Chances are, especially if you're American, the sabre-tooth cat you've heard most about is Smilodon. This is actually three different species of cat, albeit very closely related. The largest was about the size of a lion, but with a short tail, like a bobcat. They used to live in both North and South America, and died out only around 10,000 years ago, perhaps not coincidentally shortly after humans became numerous on those continents. (Not, one assumes, that humans would have hunted Smilodon themselves - but they may well have eaten much of the cats' preferred prey).