Why are lemurs only found in Madagascar?

There are more than 100 species of lemurs on Madagascar, with the total number changing often as scientists determine their genetic identities and relationships more precisely. These unique early primate animals are of interest specifically because of their place in human evolutionary history. They share our primate characteristics of forward facing eyes, five digits with nails (instead of claws), a partially opposable thumb, capability for bipedal locomotion, excellent color vision, complex social groups, and relatively long life and slow development.

Black and white Ruffed Lemurs are one of the largest lemurs, both in length and weight. They are entirely arboreal and spend their time high in the canopy of seasonal rainforests of eastern Madagascar.

Gray Bamboo Lemurs, as their name suggests, eat bamboo, and have more manual dexterity and hand-eye coordination than other lemur species. There are three subspecies, all in decline in numbers because of loss of habitat and hunting pressure.

Coquerel’s Sifaka occur in the dry deciduous forest of northwestern Madagascar. With their long hind limbs, they are agile jumpers, making their way from ground to tree, and from tree branch to branch. They use the same arboreal jumping motion on the ground as they jump from place to place, as shown in the video below.

Because of its proximity to the East African coast, it was thought that lemurs had spread to Madagascar before the island separated from Africa during tectonic movements of the Indian plate in the mid-Mesozoic, 160 million years ago. However, recent fossil evidence indicates that lemurs actually evolved in Africa from an early primate lineage only about 50 million years ago, long after the island had separated from Africa. Current thinking is that the progenitors of Lemurs may have rafted across the Mozambique Channel and established themselves in the pristine rainforests of Madagascar, the first placental mammals to do so. The earlier progenitors of lemurs in Africa eventually became extinct there, replaced by other, more clever and intelligent primates like the monkeys, leaving their only descendants on Madagascar.

Female Black Lemurs are brown, with white ear tuffs, distinguishing them from the male (below). This almost two foot tall lemur has a tail as long as its body.

Male Black Lemur. This species lives in the moist forests of northwestern Madagascar.

For the past 40-50 million years, lemurs have evolved in isolation on Madagascar, undergoing extensive adaptive radiation into many environments on the island and many niches in those environments, resulting in the huge variety of species on the island today. Isolated from other mammalian competitors, the lemurs didn’t have to compete with other arboreal species, like squirrels.

Ring-tailed Lemurs are a favorite in zoos. This individual (male?) checked us out before allowing his troop members to cross the trail in front of us.

Explosive radiation!

Why are there are so many different kinds of colorful warblers?  Taxonomists have reclassified an amazing 37 species in the genus Setophaga based on their genetic similarities.   This represents an explosion of diversity — an adaptive radiation —  in the small insectivorous bird niche.  But unlike other classic examples of this kind of diversification in birds, like Darwin’s finches on the Galapagos Islands that differ in bill size and shape to exploit different types of seeds, the explosive radiation of warblers derives primarily from their behavioral differences in where they like to feed, as well as differences in plumage color and song.

Among the 37 we managed to photograph several that fly through Minnesota on their way to Canada and Alaska to breed.

One of the first warblers to arrive in the spring and one of the last to leave in the fall, Yellow-rumped Warblers seem like one of the most common of all warblers.  It is one of the most versatile in eating habits, taking insects from the air or eating wax-covered berries, which it has special enzymes to digest.

The warbler sporting a yarmulke type of black cap is Wilson’s Warbler, a tiny bit of gold fluff that breeds in alder and willow thickets of southern Canada after leaving its Mexican and Caribbean winter home.  You see them flash by at eye level or dipping down to the ground, always on the move and always obscured by the low vegetation in which they hunt for tiny insects.

Palm Warblers wag their tail constantly, and spend most of their time in low branches or on the ground hunting insects. They are early migrants, coming from the Caribbean and Yucatan peninsula to breed in the boreal forest of Canada where temperatures are below freezing at least 8 months of the year.

Magnolia Warblers are predominantly yellow and black, like many others, but add a necklace of black stripes as a finishing touch.  They prefer the dense coniferous forests of southern Canada. This is one of the few species whose population has actually increased in the past 50 years.

Chestnut-sided Warblers come from Central America to breed in southeastern Canada and northeastern U.S. They are typically found breeding in regenerating forests, unlike other warblers that migrate to mature deciduous or coniferous woods.

Blackpoll Warblers, flying butterballs when they migrate, double their body weight by putting on fat and fly 1800 miles non-stop over 3 days. They are the most northerly breeding warbler, going far up into the Alaskan boreal forest all the way from the Caribbean and northern South America.

Of all the spring migratory birds, I think this is my favorite. Bright flashes of color as it darts through the tops of trees, and a vivid orange throat are its trademark. It’s a long way from winter headquarters in northwestern South America to the mixed deciduous-coniferous forests of southeastern Canada.

Thirty-seven closely related variations of small insectivorous birds in just one genus out of a total of 119 species in the warbler family (Parulidae).  How did this happen?

Climate is one of the primary factors thought to be responsible for this diversity — specifically, the climate from 1-5 million years ago.  Periods when cold and ice moved south across most of Canada and the U.S. pushed warblers (and other bird species) into the southeastern corner of the U.S., intensifying competition for food, and forcing greater specialization of foraging habits.  Warmer periods promoted their movement into northern forests where they continued diversifying to forage in new niches there.  Another wave of cold and ice moving south started the cycle of specialization and diversification all over again.

The end result is a unique experiment in explosive radiation of the small insectivorous bird niche in North America.