This is a species of poison-dart frog from Tambopata, Allobates femoralis.
While not very large or particularly showy–or very poisonous, for that matter–these frogs are very interesting in that they show extreme variation throughout their range. Researchers have discovered that distinct populations that are separated by geologic barriers, such as large Amazonian rivers, have different calling patterns; some populations have a two-note call, whereas other populations have a three- or four-note call. These might seem like unimportant differences, but they may be all that are required to isolate populations and lead to speciation. For instance, if females in one region prefer males that have a four-note call, they might not breed with males that have, say, a two-note call, and over time this can cause a new species to arise from that population. Add in large rivers that form barriers to populations mixing, and you’ve got the potential for a huge amount of genetic diversity and confusion for biologists trying to understand the distribution of frog diversity here. Just another way in which the Amazon continues to reveal its biodiversity to those who pay close attention to it!
Another species of primate from Tambopata, this is the black-capped squirrel monkey (Saimiri boliviensis). Not counting the tiny tamarins, these are the smallest monkeys found in the rainforests of southeastern Peru and, as their common name suggests, are about the size of a squirrel. Squirrel monkeys forage in very large groups of up to one hundred animals or more, searching mostly for fruits and insects, although they will take small vertebrates like tree frogs or baby birds. Interestingly, here in Tambopata they can almost always be found foraging alongside the much larger brown capuchins (Cebus apella). Biologists have been trying to figure this out for decades: brown capuchins can be very aggressive, and animals the size of squirrel monkeys even make up an occasional part of their diet. So the question is this, Why do squirrel monkeys travel with the capuchins? Put another way, why do the capuchins tolerate the squirrel monkeys?
A recent study by Taal Levi et al. (2013) in northeastern South America showed that squirrel monkeys tended to be more abundant where brown capuchins were present, lending support to the long-standing hypothesis that the two species facilitate each others’ foraging. That is, more eyes on the forest might make it easier to find patchily distributed foods, such as fruiting trees or large caches of insects. Alternatively, larger groups might provide better protection from predators, as both species are food for a variety of species ranging from cats to snakes to even birds of prey. Teasing apart the importance of the various benefits associated with mixed-species groups has been difficult, and we still have much to learn.