The group of primates brings together species and individuals of very different sizes. The human being , with an average weight of 62 kilos, is one of the largest, although with great variability. The chimpanzee and bonobo come close and the male orangutan weighs about the same as the human, although in both cases, the females are lighter. Only the gorilla exceeds our weight by a margin, although it also presents great variability, especially since there are two different species of gorilla ( Gorilla gorilla and Gorilla beringei ) with two subspecies each. A male can weigh between 100 and 270 kilos, and females slightly more than half.
The vast majority of primate species are, therefore, below these weights. Among the best known are the mandrill , with males weighing up to 37 kilos; the baboon , which can reach 25 kilos; the large group of macaques , which rarely exceed 10 kilos; the howler monkey , with an average of between 5 and 7 kilos; or the light spider monkey , weighing just over 2 kilos.
Among the lighter primates are the marmosets and tamarins, belonging to the family Callitrichidae. Most weigh less than a kilo, and some species barely exceed 100 grams; this is the case of the pygmy marmoset , a monkey only 13 centimeters long.
But there is still a smaller group of primates.
Berthe’s mouse lemur
Among the primates, one of the most striking groups are the lemurs, endemic to the island of Madagascar. One of the most conspicuous genera of this group is that of the Microcebus , or mouse lemurs. It has 24 species, each smaller, the tiniest being Berthe’s mouse lemur ( Microcebus berthae ). It barely measures 9 centimeters without counting the tail —which exceeds 13 centimeters—, and weighs no more than 30 grams . It lives up to its name: it weighs and measures about the same as a common mouse.
This species was described in 2000 by a team led by Professor Rodin M. Rasoloarison, from the University of Antananarivo (Madagascar), in a study published in the International Journal of Primatology . It was named in honor of Professor Berthe Rakotosamimanana , head of the University’s department of paleontology and biological anthropology, who provided the Rasoloarison team with abundant material from collections for the study of Microcebus .
A very small habitat
Berthe’s mouse lemur is only found in two very restricted areas of the Menabe region , on the west central coast of Madagascar. Its habitat is reduced to two specific forests, Kirindy and Ambadira. They are dry deciduous forests, and preferably primary. These animals tolerate degraded environments very poorly.
Forest degradation in the area reduces the forest area available for this tiny primate. Between 2017 and 2019, 3,000 to 4,000 hectares of forest were deforested in this region each year. 2020, the year of the pandemic, was an exception: barely 400 hectares were lost; but preliminary data indicates that in 2021 deforestation grew again. The main cause is the felling and burning of forest for the cultivation of corn and peanuts.
It is estimated that in 2019, the available living area for Berthe’s mouse lemur was less than 35 000 hectares , so, if we return to deforestation rates prior to 2020, it is likely that in less than 10 years this animal will no longer have a place to live.
A critically endangered primate
Since its discovery in 2000, the population of Berthe’s mouse lemurs has been monitored and the data is devastating. The great loss of habitat to which they are subjected is reflected in a reduction in the population of a more than alarming magnitude.
The greatest impact observed was in one of the subpopulations that inhabited the Kirindy forest, which after 20 years of constant surveillance, was declared extinct in 2019. The rest of the populations subsist in deplorable conditions, and future projections are pessimistic. What is most worrying is that scientists do not expect the situation to be reversible . In fact, it is estimated that in the next three generations – between 7 and 17 years in the future – there will be a population loss of more than 80 % .
This terrible situation has caused the International Union for Conservation of Nature (IUCN) to list Microcebus berthae as a critically endangered species .
References:
Markolf, M. et al. 2022. Microcebus berthae (e. T41573A215090010). International Union for Conservation of Nature. DOI: 10.2305/IUCN.UK.2022-1.RLTS.T41573A215090010.en
Rasoloarison, RM et al. 2000. Taxonomic Revision of Mouse Lemurs (Microcebus) in the Western Portions of Madagascar. International Journal of Primatology, 21(6), 963-1019.
