Post by grrraaahhh on Apr 24, 2012 5:16:05 GMT -9
Unfortunately, the data on prehistoric bear intraspecific relations is scanty but it's a topic which IMO definitely merits its own thread. Outside contributions are welcomed. FYI, I have decided to move/merge earlier relating posts into this thread.
Same author, earlier article:
"If short-faced bears were large, aggressive scavengers capable of stealing carcasses from other large carnivores, then it seems unlikely that brown bears could dominate them in direct interference competition. And while brown bears may have preferred to feed on animal carcasses, it seems more likely that they would have avoided direct confrontation with a dominant bear.
The ecological plasticity of brown bears and their ability to hibernate may have been the keys to their ultimate survival at the end of the Pleistocene, while Arctodus, the highly specialized forager, was not able to find a niche in Holocene ecosystems. Most likely, carcass densities on Holocene landscapes fell below levels necessary to sustain minimal viable populations of short-faced bears. Since many bears hibernate to survive poor food availability during winter, this may be an indirect indication that short-faced bears, and perhaps all New World bears, never evolved this strategy to survive seasonal dietary bottlenecks.”
Paul E. Matheus, 1995, Diet and co-ecology of Pleistocene short-faced bears and brown bears in eastern Beringia. Quaternary Research 44(3):447-453.
The fossil record tells us, one bear, simply dominated the other bear and prevented its early
first migration into North America. However, the smaller brown bear would return to conquer
and colonize North America while the GSFB went extinct.
According to more recent data, the model of the GSFB as brown bear gate keeper to North America is challenged (see below article). Apparently, a small number of brown bears were able to migrate and penetrate as far south as southern Canada and the northern United States.
Abstract
Current biogeographic models hypothesize that brown bears migrated from Asia to the New World ~100 to 50 thousand years ago but did not reach areas south of Beringia until ~13 to 12 thousand years ago, after the opening of a mid-continental ice-free corridor. We report a 26-thousand-year-old brown bear fossil from central Alberta, well south of Beringia. Mitochondrial DNA recovered from the specimen shows that it belongs to the same clade of bears inhabiting southern Canada and the northern United States today and that modern brown bears in this region are probably descended from populations that persisted south of the southern glacial margin during the Last Glacial Maximum.
Matheus P, Burns J, Weinstock J, Hofreiter M (2004) Pleistocene brown bears in the mid-continent of North America. Science 306: 1150.
www.sciencemag.org/content/306/5699/1150.abstract
"Because no obvious climatic or environmental events appear to explain the extinction and recolonization of brown bears in eastern Beringia, alternative explanations need to be considered. There is a marked inverse correlation between the chronology of brown bears and the much larger, hypercarnivorous, shortfaced bears in eastern Beringia (Fig. 3A). Although the two species coexisted for at least 10,000 years (;45 to 35 ka B.P.) during the interstadial, short-faced bear fossil dates are concentrated between 35 to 21 ka B.P. when brown bears were absent. Furthermore, brown bear recolonization (;21 ka B.P.) is precisely coincident with the last record of short-faced bears in Beringia."
"Stable-isotope data (Fig. 3B) suggest that the diets of the two bear species differed substantially while they were contemporaneous. Enriched levels of 15N show that short-faced bears were carnivorous, whereas brown bears were variably omnivorous and herbivorous, similar to most noncoastal bears today (Fig. 3B) (8, 19). In contrast, during the period 21 to 10 ka B.P. following the apparent extinction of short-faced bears in Beringia, brown bears also show an enriched mean 15 N signal relative to both the pre–35 ka B.P. and modern populations. However, competitive interaction is extremely difficult to infer from the paleo-record, and several environmental factors can affect isotopic ratios. In addition, much taxonomic turnover would be expected to occur around 21 ka B.P. during the environmental changes of the early LGM. If the enriched signal does indeed reflect a higher trophic level, then it may simply indicate an increased carcass biomass availability 21 to 10 ka B.P., which presumably disappeared following the extinction of many large-mammal taxa in the terminal Pleistocene."
"Stable-isotope data (Fig. 3B) suggest that the diets of the two bear species differed substantially while they were contemporaneous. Enriched levels of 15N show that short-faced bears were carnivorous, whereas brown bears were variably omnivorous and herbivorous, similar to most noncoastal bears today (Fig. 3B) (8, 19). In contrast, during the period 21 to 10 ka B.P. following the apparent extinction of short-faced bears in Beringia, brown bears also show an enriched mean 15 N signal relative to both the pre–35 ka B.P. and modern populations. However, competitive interaction is extremely difficult to infer from the paleo-record, and several environmental factors can affect isotopic ratios. In addition, much taxonomic turnover would be expected to occur around 21 ka B.P. during the environmental changes of the early LGM. If the enriched signal does indeed reflect a higher trophic level, then it may simply indicate an increased carcass biomass availability 21 to 10 ka B.P., which presumably disappeared following the extinction of many large-mammal taxa in the terminal Pleistocene."
Same author, earlier article:
"If short-faced bears were large, aggressive scavengers capable of stealing carcasses from other large carnivores, then it seems unlikely that brown bears could dominate them in direct interference competition. And while brown bears may have preferred to feed on animal carcasses, it seems more likely that they would have avoided direct confrontation with a dominant bear.
The ecological plasticity of brown bears and their ability to hibernate may have been the keys to their ultimate survival at the end of the Pleistocene, while Arctodus, the highly specialized forager, was not able to find a niche in Holocene ecosystems. Most likely, carcass densities on Holocene landscapes fell below levels necessary to sustain minimal viable populations of short-faced bears. Since many bears hibernate to survive poor food availability during winter, this may be an indirect indication that short-faced bears, and perhaps all New World bears, never evolved this strategy to survive seasonal dietary bottlenecks.”
Paul E. Matheus, 1995, Diet and co-ecology of Pleistocene short-faced bears and brown bears in eastern Beringia. Quaternary Research 44(3):447-453.
The fossil record tells us, one bear, simply dominated the other bear and prevented its early
first migration into North America. However, the smaller brown bear would return to conquer
and colonize North America while the GSFB went extinct.
According to more recent data, the model of the GSFB as brown bear gate keeper to North America is challenged (see below article). Apparently, a small number of brown bears were able to migrate and penetrate as far south as southern Canada and the northern United States.
Abstract
Current biogeographic models hypothesize that brown bears migrated from Asia to the New World ~100 to 50 thousand years ago but did not reach areas south of Beringia until ~13 to 12 thousand years ago, after the opening of a mid-continental ice-free corridor. We report a 26-thousand-year-old brown bear fossil from central Alberta, well south of Beringia. Mitochondrial DNA recovered from the specimen shows that it belongs to the same clade of bears inhabiting southern Canada and the northern United States today and that modern brown bears in this region are probably descended from populations that persisted south of the southern glacial margin during the Last Glacial Maximum.
Matheus P, Burns J, Weinstock J, Hofreiter M (2004) Pleistocene brown bears in the mid-continent of North America. Science 306: 1150.
www.sciencemag.org/content/306/5699/1150.abstract
