scholarly journals Silurian-Devonian boundary events and their influence on cephalopod evolution: evolutionary significance of cephalopod egg size during mass extinctions

2010 ◽  
pp. 513-540 ◽  
Author(s):  
Š. Manda ◽  
J. Frýda
Keyword(s):  
Egg Size ◽  
Evolutionary Significance ◽  
Mass Extinctions ◽  
Cephalopod Evolution

scholarly journals Trophic level & evolution in Paleozoic gastropods

1992 ◽  
Vol 6 ◽  
pp. 3-3
Author(s):  
Warren D. Allmon ◽  
Douglas H. Erwin ◽  
Robert M. Linsley ◽  
Paul J. Morris
Keyword(s):  
Trophic Level ◽  
Trophic Position ◽  
Marine Species ◽  
The Other ◽  
Evolutionary Significance ◽  
Suitable Model ◽  
Mass Extinctions ◽  
Suspension Feeders ◽  
Extinction Rates ◽  
Mode Of Life

Although trophic position or level is one of the most basic aspects of a benthic marine species' ecology, its evolutionary significance remains obscure. Gastropods offer a suitable model for examining the relationship between trophic level and evolution since they exhibit a wide variety of trophic strategies and their mode of life is often reflected in their shell form. We examined 196 genera of Paleozoic gastropods (≈ 1/3 of known genera) for which first appearance and last appearance could be specified to stage level and for which trophic strategy could be inferred with a reasonable degree of confidence. We classified these genera into four trophic categories on the basis of shell characters relating to locomotion and clamping. These trophic categories are: Suspension feeders, Grazers on firm substrata, Soft substrate Grazers/Detritivores, and Carnivores. Suspension feeders are the most unambiguously recognizable category, marked by clear indicators of a sessile mode of life such as a radial apertures and planispiral shell forms. Our central observation from these data is that suspension feeders have shorter generic longevities than the other three trophic groups. This pattern is robust to a variety of methods of analysis. The mean generic longevity of the suspension feeders is 15 MY less than the other trophic categories. Cumulative frequency of genera within trophic categories versus log duration shows suspension feeders to be statisticaly significantly shorter lived than the other three trophic categories. The other three categories are not distinguishable. This pattern is unchanged by the removal of taxa dying out at mass extinctions. Suspension feeders have lower origination rates and higher extinction rates than the other trophic classes. This is not a taxonomic artifact produced by ornamentation and the number of characters available. This background pattern is also present in the end Ordovician and Late Devonian mass extinctions. Suspension feeders loose about half their genera in these extinctions, the two classes of grazers loose about 1/3 of their genera, and the carnivores suffer almost no extinctions. Suspension feeding appears to carry a significant evolutionary detriment in both mass extinctions and background times. This may be reflected in the change in trophic distribution of gastropods from the Ordovician to the Recent. The end Permian extinction shows a different pattern of selectivity; detritivores suffer the least.

Catastrophes and Lesser Calamities

2004 ◽  
Author(s):  
Tony Hallam
Keyword(s):  
Big Five ◽  
Homo Sapiens ◽  
Oxygen Deficiency ◽  
Climatic Changes ◽  
Evolutionary Significance ◽  
Mass Extinctions ◽  
The Past ◽  
Extinction Events ◽  
Life On Earth ◽  
Climatic Cooling

In Catastrophes and Lesser Calamities, renowned geologist Tony Hallam takes us on a tour of the Earth's history, and of the cataclysmic events, as well as the more gradual extinctions, that have punctuated life on Earth throughout the past 500 million years. While comparable books in this field of study tend to promote only one likely cause of mass extinctions, such as extraterrestrial impact, volcanism, and or climatic cooling, Catastrophes and Lesser Calamities breaks new ground, as the first book to attempt an objective coverage of all likely causes, including sea-level and climatic changes, oxygen deficiency in the oceans, volcanic activity, and extraterrestrial impact. Hallam focuses on the so-called 'big five' mass extinctions, at the end of the Ordovician, Permian, Triassic, and Cretaceous periods, and the later Devonian, and he also includes less well-known examples where relevant. He devotes attention especially to the attempts by geologists to distinguish true catastrophes from more gradual extinction events, and he concludes with a discussion of the evolutionary significance of mass extinctions, and on the influence of Homo sapiens in causing extinctions within the last few thousand years, both on land and in the seas.

The evolutionary significance of mass extinctions

2004 ◽  
Author(s):  
Tony Hallam
Keyword(s):  
Biotic Interactions ◽  
Evolutionary Significance ◽  
Red Queen Hypothesis ◽  
Mass Extinctions ◽  
Red Queen ◽  
Physical Conditions ◽  
The Face ◽  
Competition For Food ◽  
Zero Sum ◽  
The Red Queen

Darwin was firmly of the opinion that biotic interactions, such as competition for food and space – the ‘struggle for existence’ – were of considerably greater importance in promoting evolution and extinction than changes in the physical environment. This is clearly brought out by this quotation from The Origin of Species: . . . Species are produced and exterminated by slowly acting causes . . . and the most important of all causes of organic change is one that is almost independent of altered . . . physical conditions, namely the mutual relation of organism to organism – the improvement of one organism entailing the improvement or extermination of others. . . . The driving force of competition in a crowded world is also stressed in another quotation presenting Darwin’s famous wedge metaphor: . . . In looking at Nature, it is most necessary . . . never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or the old, during each generation . . . The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force. . . . The implication of the Darwinian view concerning the dominance of biotic competition is that for each winner there is a loser – a kind of zero-sum game. It has been accepted more or less uncritically by generations of evolutionary biologists, but not until the 1970s did it become graced with a name – the Red Queen hypothesis. The story behind the emergence of this name is an interesting one. At the beginning of the 1970s the rather eccentric University of Chicago palaeobiologist Leigh Van Valen did some interesting research concerning the analysis of survivors of Phanerozoic taxa which suggested that the probability of a fossil group becoming extinct was more or less constant in time. To account for this, Van Valen put forward his Red Queen hypothesis.

Effects of Predation and Trophic Conditions on the Reproduction of Tylototriton verrucosus (Caudata: Salamandridae) in Darjeeling

2011 ◽  
Vol 4 (2) ◽  
pp. 163-169 ◽  
Author(s):  
Ritwik Dasgupta
Keyword(s):  
Frequency Distribution ◽  
Primary Productivity ◽  
Egg Size ◽  
Zooplankton Abundance ◽  
Trophic Conditions ◽  
Size Frequency Distribution ◽  
Size Frequency ◽  
High Predation ◽  
Hatchling Size ◽  
Predation Rates

The facts that small hatchlings emerged from small eggs laid under high predation levels prevailing at the lower altitudes of distribution of this species in Darjeeling while larger hatchlings emerged from larger eggs laid under lower levels of predation at higher altitudes, show that predation is not selected for large egg and initial hatchling size in this salamandrid species. Metamorphic size was small under high predation rates because this species relied on crypsis for evading predators. Egg and hatchling size are related inversely to levels of primary productivity and zooplankton abundance in lentic habitats. Hatchling sizes are related positively to egg size and size frequency distribution of zooplankton. Small egg and small hatchling size have been selected for at the lower altitudes of distribution of this salamandrid in Darjeeling because predation rates increased in step with improvement in trophic conditions at the lower altitudes.

Sign in / Sign up

Export Citation Format

Share Document