Efecto Alee, o cómo extinguirse por mala suerte | Cuaderno de ... Capra pyrenaicaEl bucardo, o cabra montesa pirenaica (Capra pyrenaica), se encuentra actualmente extinta, a pesar de haber dominado durante siglos la cordillera que le da su nombre. El día 6 de Enero de 2000, un abeto seco cayó sobre el último ejemplar de esta especie, llevándola a la extinción. Se trata, sin duda, de un ejemplo de "mala suerte", una casualidad con efectos devastadores.
Este ejemplo no es único. Existen distintas especies sujetas a lo que se conoce como efectos estocásticos, situaciones en las que el azar y la casualidad tienen un peso determinante. En el caso del bucardo, el azar tomó la forma de un abeto seco y podrido, pero ya era una especie muerta en vida cuando eso ocurrió. Los últimos tres individuos de la especie eran hembras, con lo que era imposible que se reprodujesen. Dusky Seaside Sparrow En Biología de la Conservación, a esto se le conoce como efecto Allè o efecto Allee. Claro, que a veces reproducirse es casi peor. Lince Consanguineidad. Collapse: How Societies Choose to Fail or Succeed - Wikipedia ... Synopsis[edit] In the prologue, Diamond summarizes his methodology in one paragraph: This book employs the comparative method to understand societal collapses to which environmental problems contribute. My previous book (Guns, Germs, and Steel: The Fates of Human Societies), had applied the comparative method to the opposite problem: the differing rates of buildup of human societies on different continents over the last 13,000 years.
In the present book focusing on collapses rather than buildups, I compare many past and present societies that differed with respect to environmental fragility, relations with neighbors, political institutions, and other "input" variables postulated to influence a society's stability. The "output" variables that I examine are collapse or survival, and form of the collapse if collapse does occur.
By relating output variables to input variables, I aim to tease out the influence of possible input variables on collapses.[1] Book structure[edit] Reviews[edit] Are We in the Middle of a Sixth Mass Extinction? Earth's creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the dinosaurs. That's the conclusion of a new study, which calculates that three-quarters of today's animal species could vanish within 300 years. "This is really gloom-and-doom stuff," says the study's lead author, paleobiologist Anthony Barnosky of the University of California, Berkeley.
"But the good news is we haven't come so far down the road that it's inevitable. " Species naturally come and go over long periods of time. But what sets a mass extinction apart is that three-quarters of all species vanish quickly. Earth has already endured five mass extinctions, including the asteroid that wiped out dinosaurs and other creatures 65 million years ago. Barnosky and colleagues took on this challenge by looking to the past. The picture gets even grimmer when all mammals currently endangered or threatened are added to the count. Top 10 Civilizations That Mysteriously Disappeared. Throughout our history, most civilizations have either met a slow demise or were wiped out by natural disasters or invasion. But there are a few societies whose disappearance has scholars truly stumped: 10.
The Olmec One of the first Mesoamerican societies, the Olmec inhabited the tropical lowlands of south-central Mexico. Where did they go? Around 400 BC the eastern half of the Olmec’s lands was depopulated- possibly due to environmental changes. 9. The Nabateans were a Semitic culture that inhabited parts of Jordan, Canaan and Arabia from around the sixth century BC. During the fourth century AD, the Nabateans abandoned Petra and no one really knows why. 8. The Aksumite Empire began in the first century AD in what is now Ethiopia and is believed to be the home of the Queen of Sheba. According to local legend, a Jewish Queen named Yodit defeated the Aksumite Empire and burned its churches and literature. 7.The Mycenaeans 6. 5.The Cucuteni-Trypillian Culture 4. 3.The Minoans 2.The Anasazi 1.
Extinction rates 'overestimated', says study. 19 May 2011Last updated at 03:51 By Mark Kinver Science and environment reporter, BBC News The authors acknowledge that the study does not mean concerns for biodiversity can be put on ice Current extinction rate projections may be overestimating the role of habitat loss on species, a study suggests. Current methods are too simplistic and fail to take into account the full complexity of what influences species numbers, researchers observed. Writing in the journal Nature, they said present figures overestimated rates by up to 160%, and called for updated, more accurate calculations. But they did add that habitat loss was still the main threat to biodiversity. Co-authors Professor Stephen Hubbell, from the University of California Los Angeles, and Professor Fangliang He, from Sun Yat-sen University, China, said existing mathematical models were flawed.
"Estimates based on this method are almost always much higher than actually observed. " 'Severe reservations' A Short, Simple Introduction to Information Theory - a knol by Ryan Moulton. Forum: A Study of History: the rise and fall of civilizations. Societal collapse. What distinguishes the more dramatic failures of human societies, seeming to deserve the term "collapse", from less dramatic long term decline is not widely agreed on.
The subject may include any other long term decline of a culture, its civil institutions or other major characteristics of it as a society or a civilization. Causes of collapse[edit] Common factors that may contribute to societal collapse are economic, environmental, social and cultural, but they manifest combined effects like a whole system out of balance. In some cases a natural disaster (e.g. tsunami, earthquake, massive fire or climate change) may seem to be an immediate cause. Other factors such as a Malthusian catastrophe, overpopulation or resource depletion might be the proximate cause of collapse. Significant inequity may combine with lack of loyalty to a central power structure and result in an oppressed lower class rising up and taking power from a smaller wealthy elite. Population dynamics[edit] Other features.