Jan Ekman, Professor, Head of Population Biology

Publications

Contact

E-mail
jan.ekman[AT]ebc.uu.se

Address
Dept of Ecology and Evolution
Population Biology
Norbyvägen 18 D
SE-752 36 Uppsala
Sweden

Telephone
+46 018-471 2627

Telefax
+46 18 471 6424

Research

Evolution of the family

Many animals live in family associations. From an evolutionary viewpoint this behaviour is a challenge. Family living could promote cooperation and seemingly unselfish behaviour. Individuals may gain evolutionary success not only by through the "self" but they can also propagate of their genes from helping relatives. Relatedness is defined from that individuals to some extect have identical genes through a shared ancestry. Behaviour would hence only be unselfish from the point of the well-being of the "self" while cooperation with relatives would help to multilply the genes of the "self". Simultaneously there is a conflict while breeding among close relatives carries inbreeding costs, and offspring reproduction is therefore often suppressed in families. In reality family formation often seems to be linked to environmental conditions. The offspring would do better by breeding on their own but they cannot find resources of their own in a crowded population. The role of cooperation seems to be mainly to serve as an incentive for the offspring to wait for a breeding opportunity in the family, while the emergence of free resources would account for why the offspring leave despite the benefits of family cooperation.

I have followed the formation of families as the offspring stay on, sometime for several years, in a population of the Siberian jay, Perisoreus infaustus, in northern Sweden. The study started in 1989 and is still running. The aim has been to link the evolutionary success (production of offspring over life) of the offspring to for how long they stay in their family. The family provides shelter during early years and offspring which wait in their family survive better than those which leave immediately. Offspring which stay in the family also obtain better territories when the leave and prtoduce more offspring over life. Overall the behaviour of postponing the age of independence is a balance between the loss of reproduction early in life as balanced against gaining better resources once independent. Many questions still remains to be solved. One of the more central is how the variation in behaviour (leaving immediately/or remaining in the family) is inherited and why the behaviour of leaving early is not weeded out by evolution.

Another avenue of these studies is to follow how family living changed as new species have evolved and spread over the globe. Here I have worked with corvids, which have their origin from Australia/New Guinea. Their ancestors left the AustaloPapuan area around 30 million years age and have since colonized most of the globe while a large number of new species have evolved. The history of diversification has been reconstructed using molecular techniques (DNA). The ancestors of the corvids were family living. As they spread to the northern hemisphere several lost the behaviour of cooperation and family living. This is probably linked to a harsher climate. The climate on southern hemisphere landmasses is tropical or subtropical while it is temperate and boreal on the northern hemisphere. The harsher climate means that competition is more severe on the northern hemisphere and the conflict would fall on relatives if families stayed together during the winter. Competition is not as severe during the mild winter on the southern hemisphere but cooperation in finding food and escaping predators would be more important.

Global demise of the megafauna

The majority of the world's megafauna (usually defined as species over 20kg) has been lost during the last 50000 years. For instance a large number of large marsupials have gone extinct in Australia. The fauna of the New World included several elephants, camels, giant sloths and many more large species which went extinct 10000-15000 years ago. Madagascar had up to 17 species of giant lemurs, some as large as today's gorilla, which have gone extinct the last 2000 years. There were the moa birds on New Zealand. These are a few examples. Several hypotheses have been proposed as an explanation for the demise of the megafauna. There is overall a link between the appearance of modern man in an area and the disappearance of the large mammals. This is the so called "Blitzkrieg" model. There are opposing models but so far they have not been able to account for the link in time between apperance of early human/megafauna demise. One problem in establishing the role of modern man is that the disappearance of the megafauna often has to be assessed from natural assemblies of animals which have died a natural death, while there is still little tangible evidence for hunting. This could probably be due to that human populations were scrace but the data is still missing.

I have studied the fauna on the Zanzibar island dating back 30000 years. This area was a peninsula during the last glaciation (~20000 to 12000) years ago when the sea level was about 120 m lower than today and the fauna was then part of the one on the East African mainland. Todays straight to the mainland was then a landbridge being only 47 m deep. As the water level rose when the ice melted Zanzibar became an island and the fauna isolated from the mainland. Together with archaeologists and molecular biologists I have studied the bone remains from a cave on Zanzibar which was occupied by man up to start of the last glacial maximum (up to around 20000 years ago) and which was then reoccupied about 7-8000 years ago. Using traditional morphology but also "ancient DNA" techniques we have been able to identify large mammals which now are absent from the island and for which there are no records or recollections among the local population. We have a well dated stratigraphy running from 8000 years ago and up to now which allows us to follow in detail the change in composition of the megafauna. Furthermore, the material represents the left overs from hunting so we do here have the "smoking gun" of the role of man.