Late Cenozoic onset of the latitudinal diversity gradient of North American mammals
Authors:
Marcot et al
Abstract:
The decline of species richness from equator to pole, or latitudinal diversity gradient (LDG), is nearly universal among clades of living organisms, yet whether it was such a pervasive pattern in the geologic past remains uncertain. Here, we calculate the strength of the LDG for terrestrial mammals in North America over the past 65 My, using 27,903 fossil occurrences of Cenozoic terrestrial mammals from western North America downloaded from the Paleobiology Database. Accounting for temporal and spatial variation in sampling, the LDG was substantially weaker than it is today for most of the Cenozoic and the robust modern LDG of North American mammals evolved only over the last 4 My. The strength of the LDG correlates negatively with global temperature, suggesting a role of global climate patterns in the establishment and maintenance of the LDG for North American mammals.
pop sci write up.
Phanerozoic diversity and neutral theory
Authors:
Holland et al
Abstract:
Although Phanerozoic increases in the global richness, local richness, and evenness of marine invertebrates are well documented, a common explanation for these patterns has been difficult to identify. Evidence is presented here from marine invertebrate communities that there is a Phanerozoic increase in the fundamental biodiversity number (θ), which describes diversity and relative abundance distributions in neutral ecological theory. If marine ecosystems behave according to the rules of Hubbell's Neutral Theory of Biodiversity and Biogeography, the Phanerozoic increase in θ suggests three possible mechanisms for the parallel increases in global richness, local richness, and evenness: (1) an increase in the per-individual probability of speciation, (2) an increase in the area occupied by marine metacommunities, and (3) an increase in the density (per-area abundance) of marine organisms. Because speciation rates have declined over time and because there is no clear evidence for an increase in metacommunity area through the Phanerozoic, the most likely of these is an increase in the spatial density of marine invertebrates over the Phanerozoic, an interpretation supported by previous studies of fossil abundance. This, coupled with a Phanerozoic rise in body size, suggests that an increase in primary productivity through time is the primary cause of Phanerozoic increases in θ, global richness, local richness, local evenness, abundance, and body size.
Response of deep-sea biodiversity to abrupt deglacial and Holocene climate changes in the North Atlantic Ocean
Authors:
Yasuhara et al
Abstract:
Aim
Little is known about how marine biodiversity responds to oceanographic and climatic changes over the decadal to centennial time-scales which are most relevant for predicted climate changes due to greenhouse gas forcing. This paper aims to reveal decadal–centennial scale deep-sea biodiversity dynamics for the last 20,000 years and then explore potential environmental drivers.
Location
The North Atlantic Ocean.
Methods
We investigated deep-sea benthic microfossil records to reveal biodiversity dynamics and subsequently applied comprehensive ecological modelling to test possible environmental factors (i.e. surface productivity, seasonality of productivity or deepwater circulation related to bottom-water temperature) that may have influenced deep-sea biodiversity over these time-scales.
Results
Deep-sea biodiversity changed synchronously with stadial–interstadial climate changes over the last 20,000 years across a large area of the North Atlantic in both ostracod crustaceans and foraminiferan protozoa (in spite of their different dispersal abilities). Species diversity rapidly increased during abrupt stadial events during the last deglacial and the Holocene interglacial periods. These include the well-known Heinrich 1, the Younger Dryas and the 8.2 ka events when the strength of Atlantic Meridional Overturning Circulation (AMOC) decreased. There is also evidence for quasi-cyclic changes in biodiversity at a c. 1500-year periodicity, consistent with the well-known ‘1500-year climatic cycle’. Statistical analyses revealed that AMOC variability (probably specifically the variability in AMOC-driven bottom-water temperature) is correlated with deep-sea biodiversity.
Main conclusions
Our finding of a significant AMOC–diversity relationship may indicate pervasive control of the diversity of deep-sea benthic species by rapidly changing climate, specifically bottom-water temperature, over decadal to centennial time-scales. Our results, based on highly resolved fossil records, may portend pervasive, synchronous and sudden ecosystem responses to human-induced changes to climate and ocean circulation in this century.
Observations of insects
and their feeding marks on leaves in modern forests confirm indications
from fossil leaf deposits that the diversity of chewing damage relates
directly to diversity of the insect population that created it,
according to an international team of researchers.
"The
direct link between richness of leaf-chewing insects and their feeding
damage across host plants in two tropical forests validates the
underlying assumptions of many paleobiological studies that rely on
damage-type richness as a means to infer changes in relative herbivore
richness through time," the researchers report in today's (May 2) issue
of a.
Studies of leaf chewing include observation of
the leaves, but rarely include all the insects that actually made the
marks. Mónica R. Carvalho, graduate student, Cornell University and
Peter Wilf, professor of geosciences, Penn State, and colleagues looked
at leaf predation in two tropical forests in Panama to test for a
relationship between the richness of leaf-chewing insects and the leaf
damage that the same insects induce.
Using Smithsonian
Tropical Research Institute canopy-access cranes and working in the dark
at almost 200 feet high in the treetops at new moon during two summers
the researchers collected a total of 276 adult and immature leaf-chewing
insects of 156 species. While the largest category of insect was
beetles, leaf chewers among grasshoppers, stick insects and
caterpillars, as well as a few ants, were also collected.
The
team also collected fresh leaves of the insects' host plants and placed
the insects in feeding experiment bags with these leaves. They allowed
adult insects to feed for two to three days and immature stages to feed
until full maturity when possible. The researchers then classified the
damage to the leaves into categories, in the same way they catalog
fossil leaf- chewing damage.
"This is the first attempt
to compare leaf-chewing damage inflicted by many kinds of living
insects on many kinds of plants throughout a large forest area, both to
the culprit insects and to the leaf damage we see in the fossil record,"
said Carvalho. "We mounted 276 of the insects with their damaged leaves
and deposited them in the STRI Insect Collection."
This
collection is the only known vouchered collection of diverse,
identified insects and their feeding damage on leaves of identified
plant hosts.
The number of collected insect species
correlated strongly with the number of damage types recorded in canopy
leaves of 24 tree and liana species observed in the feeding experiments.
This suggests that the number of types of damage seen in the fossil
record is also related to the actual diversity of damage-making insects.
The
researchers also compared the modern leaf data to fossil data from
Colombia, Argentina, the Great Plains and the Rocky Mountains. They
found that the distribution of chewing marks was the same across both
modern and ancient settings, showing a striking consistency in how
insects have divided up their leaf resources since at least the end of
the age of dinosaurs.
A new study of re-growing tropical forests has concluded that plant biodiversity takes longer to recover than carbon storage following major disturbances such as clearance for farming.
The findings, published in the scientific journal Proceedings of the Royal Society B, have important implications for conservation since there are now many re-growing forests in South and Central America. The new study is the first large-scale analysis of the recovery of both plant biodiversity and carbon pools in re-growing forests.
Over half of all tropical forests have already been converted for agriculture, logged or burnt in the recent past. Re-growing forests could help both to soak up carbon emissions produced by human activities and to reduce species' extinctions.
The scientists, from the Centre for Ecology & Hydrology and Bournemouth University, concluded that although carbon recovered most quickly, even after 80 years re-growing forests tended to have less carbon than old-growth forests. This is probably because these forests are often dominated by small, fast growing trees. It may take centuries for larger trees which hold more carbon to become established.
In contrast, although the number of tree species recovered relatively rapidly, many species characteristic of old-growth forests were rare in re-growing forests. This is worrying because these species are probably those most vulnerable to extinction.
Mammal disparity decreases during the Cretaceous angiosperm radiation
Authors:
David M. Grossnickle and P. David Polly
Abstract:
Fossil discoveries over the past 30 years have radically transformed traditional views of Mesozoic mammal evolution. In addition, recent research provides a more detailed account of the Cretaceous diversification of flowering plants. Here, we examine patterns of morphological disparity and functional morphology associated with diet in early mammals. Two analyses were performed: (i) an examination of diversity based on functional dental type rather than higher-level taxonomy, and (ii) a morphometric analysis of jaws, which made use of modern analogues, to assess changes in mammalian morphological and dietary disparity. Results demonstrate a decline in diversity of molar types during the mid-Cretaceous as abundances of triconodonts, symmetrodonts, docodonts and eupantotherians diminished. Multituberculates experience a turnover in functional molar types during the mid-Cretaceous and a shift towards plant-dominated diets during the late Late Cretaceous. Although therians undergo a taxonomic expansion coinciding with the angiosperm radiation, they display small body sizes and a low level of morphological disparity, suggesting an evolutionary shift favouring small insectivores. It is concluded that during the mid-Cretaceous, the period of rapid angiosperm radiation, mammals experienced both a decrease in morphological disparity and a functional shift in dietary morphology that were probably related to changing ecosystems.
