Biotic Differentiation Research Articles

Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Perú

Subsequent to our initial reports of the discovery of Deseadan fossils in southern Perú, we have obtained new data regarding the paleontology and geology of the upper member of the Moquegua Formation. These data include newly recovered fossil specimens and further analyses of those collected in our earlier field seasons. We have also obtained an ash directly from within the fossil-bearing units near the summit of Cerro Pan de Azúcar. Biotites from this Sugarloaf ash give an age estimate of 26.25 ± 0.10 Ma, thus supporting our previous suggestion that these fossil-bearing horizons are of late Oligocene age (Deseadan South American Land Mammal “Age”) and removing our query regarding a possible early Miocene age. Most of the fossils are of notoungulates and most of these are trachytheriine mesotheriids. Remarkably, three distinct mesotheriid taxa appear to have been present in the Moquegua fauna, none of which are referable to the common Trachytherus alloxus of the nearby and at least partly contemporaneous Salla beds of Bolivia. Other fossils documented here include postcranial elements of the notohippid notoungulate, Moqueguahippus, a macraucheniid litoptern (cf. Coniopternium), an osteoderm of an unnamed species of armadillo (Dasypodidae, cf. Dasypodinae), and a claw of a phorusrhacid bird. We also describe a diminutive new hystricognath rodent, Sallamys quispea, sp. nov. It is similar to, but distinct from, S. pascuali of Salla. Indeed, despite the temporal and geographic proximity of Moquegua to Salla, none of the taxa from Moquegua that can be identified to species are known from Salla. Likewise, we have failed to find any dasypodids from Salla that have osteoderms like that described in this work. Thus, it is appears that distinctive paleogeographic and paleoenvironmental conditions in the late Oligocene led to a regional biotic differentiation for the Moquegua area of coastal Perú.

Yagonia Roberts (Brachiopoda: Chonetidina) from the Malimán Formation, Lower Carboniferous of western Argentina: palaeobiogeographical implications

A new anoplid chonetid species, Yagonia furquei sp. nov., is described from the Lower Carboniferous (late Tournaisian–early Viséan) Malimán Formation of western Argentina. The associated temperate ‘Malimanian’ fauna is suggested to indicate an initial biotic segregation that took place in western Gondwana (southwestern South America), a palaeobiogeographic event that predated the late Viséan global cooling and associated major palaeolatitudinal biotic differentiation. Occurrences of Yagonia are here interpreted as evidence of a ‘south to north’ faunal migration pathway, here named the Austropanthalassic–Rheic oceanic corridor, established in western Gondwana during the late Early Carboniferous.

Biogeographic reconstructions for the North Pacific Oligocene shelf zones: comparison of “warm” Eocene and “cold” Oligocene

Recent investigations in Kamchatka and Sakhalin in the active transitional zone from the Pacific Ocean to the Asian Continent have led to a new generation of Cenozoic stratigraphic schemes. Several regional stages recording distinctive phases of regional development and different biotic and abiotic events have been recognized. The following regional stages were distinguished in Kamchatka: the Yuzhno-Il’pinskii (Paleocene), Kylanskii, Kilakirnunskii, Gailkhavilanskii (Eocene), and the Aluginskii (Oligocene). All of them contain planktonic and benthic foraminifers, mollusks, macroflora, and diatoms. Therefore, standard stages and zones can be outlined there. The Paleocene and Eocene zones were established by means of planktonic foraminifers, and the Oligocene zones by diatoms. In addition, provincial zones based on benthic assemblages were recognized, which can be used for regional correlations. Recently some new data on magnetostratigraphy and biomarkers became available. The regional stages were also characterized in terms of lithology with outlining sedimentary cycles. In the warm Eocene conditions, carbonate plankton, warm-water mollusks, and paratropical flora were spread over the entire North Pacific, whereas a cold-water (boreal type) biota was formed during the Oligocene and the warmwater associations migrated southward. So, the main biotic differentiation took place during Eocene to Oligocene.

Nuclear and mitochondrial phylogeography of the Atlantic forest endemic Xiphorhynchusfuscus (Aves: Dendrocolaptidae): Biogeography and systematics implications

We studied the intraspecific evolutionary history of the South American Atlantic forest endemic Xiphorhynchus fuscus (Aves: Dendrocolaptidae) to address questions such as: Was the diversification of this bird’s populations associated to areas of avian endemism? Which models of speciation (i.e., refuges, river as barriers or geotectonism) explain the diversification within X. fuscus? Does the genetic data support subspecies as independent evolutionary units (species)? We used mitochondrial ( n = 34) and nuclear ( n = 68) DNA sequences of X. fuscus to study temporal and spatial relationships within and between populations. We described four main monophyletic lineages that diverged during the Pleistocene. The subspecies taxonomy did not match all the evolutionary lineages; subspecies atlanticus was the only one that represented a monophyletic and isolated lineage. The distribution of these lineages coincided with some areas of endemism for passerines, suggesting that those areas could be regions of biotic differentiation. The ancestor of X. fuscus diverged ∼3 million years ago from Amazonian taxa and the phylogeographic pattern suggested that X. fuscus radiated from northeastern Brazil. Neither the riverine nor the geotectonic vicariance models are supported as the primary cause for diversification of geographic lineages, but rainforest contractions and expansions (ecological vicariance) can explain most of the spatial divergence observed in this species. Finally, analyses of gene flow and divergence time estimates suggest that the endangered subspecies atlanticus (from northeastern Brazil) can be considered a full species under the general lineage species concept.

HOMOGENIZATION DYNAMICS AND INTRODUCTION ROUTES OF INVASIVE FRESHWATER FISH IN THE IBERIAN PENINSULA

Nonnative invasive species are one of the main global threats to biodiversity. The understanding of the traits characterizing successful invaders and invasion-prone ecosystems is increasing, but our predictive ability is still limited. Quantitative information on biotic homogenization and particularly its temporal dynamics is even scarcer. We used freshwater fish distribution data in the Iberian Peninsula in four periods (before human intervention, 1991, 1995, and 2001) to assess the temporal dynamics of biotic homogenization among river basins. The percentage of introduced species among fish faunas has increased in recent times (from 41.8% in 1991 to 52.5% in 2001), leading to a clear increase in the similarity of community composition among basins. The mean Jaccard's index increase (a measure of biotic homogenization) from the pristine situation to the present (17.1%) was similar to that for Californian fish but higher than for other studies. However, biotic homogenization was found to be a temporally dynamic process, with finer temporal grain analyses detecting transient stages of biotic differentiation. Introduced species assemblages were spatially structured along a latitudinal gradient in the Iberian Peninsula, with species related to sport fishing being characteristic of northern basins. Although the comparison of fish distributions in the Iberian Peninsula and France showed significant and generalized biotic homogenization, nonnative assemblages of northeastern Iberian basins were more similar to those of France than to those of the rest of the Iberian Peninsula, indicating a main introduction route. Species introduced to the Iberian Peninsula tended to be mainly piscivores or widely introduced species that previously had been introduced to France. Our results indicate that the simultaneous analysis of the spatial distribution of introduced assemblages (excluding native species that reflect other biogeographical patterns) and their specific traits can be an effective tool to detect introduction and invasion routes and to predict future invaders from donor regions.

Biotic homogenization: a new research agenda for conservation biogeography

AbstractAim Biotic homogenization describes the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more biotas over a specified time interval. The study of biotic homogenization is a young and rapidly emerging research area in the budding field of conservation biogeography, and this paper aims to synthesize our current knowledge of this process and advocate a more systematic approach to its investigation.Methods Based on a comprehensive examination of the primary literature this paper reviews the process of biotic homogenization, including its definition, quantification, underlying ecological mechanisms, environmental drivers, the empirical evidence for different taxonomic groups, and the potential ecological and evolutionary implications. Important gaps in our knowledge are then identified, and areas of new research that show the greatest promise for advancing our current thinking on biotic homogenization are highlighted.Results Current knowledge of the patterns, mechanisms and implications of biotic homogenization is highly variable across taxonomic groups, but in general is incomplete. Quantitative estimates are almost exclusively limited to freshwater fishes and plants in the United States, and the principal mechanisms and drivers of homogenization remain elusive. To date research has focused on taxonomic homogenization, and genetic and functional homogenization has received inadequate attention. Trends over the past decade, however, suggest that biotic homogenization is emerging as a topic of greater research interest.Main conclusions My investigation revealed a number of important knowledge gaps and priority research needs in the science of biotic homogenization. Future studies should examine the homogenization process for different community properties (species occurrence and abundance) at multiple spatial and temporal scales, with careful attention paid to the various biological mechanisms (invasions vs. extinctions) and environmental drivers (environmental alteration vs. biotic interactions) involved. Perhaps most importantly, this research should recognize that there are multiple possible outcomes resulting from the accumulation of species invasions and extinctions, including biotic differentiation whereby genetic, taxonomic or functional similarity of biotas decreases over time.

Do Exotics Homogenize or Differentiate Communities? Roles of Sampling and Exotic Species Richness

It is commonly asserted that exotic species promote the homogenization of biological communities. However, theoretical evidence implies that exotic species may often have the opposite effect, of differentiating biological communities where different exotic species become established in different areas. Furthermore, few empirical studies have directly measured the homogenizing effects of exotics. In this study, I used the plant inventories of 20 localities in the United States to measure whether exotic plant increased the similarity of those localities. I calculated Jaccard's index of similarity (JI) for exotic species and then for native species to see if the exotic JI was consistently higher when comparing two localities. I found that JI for both exotic and native species decline exponentially with increasing distance and latitude separation between localities so that localities that share many native species also tend to share many exotic species. More importantly, in nearly half of the pairwise locality comparisons (87 of 190), the (JIexotic/JInative) ratio is less than one, indicating a slight tendency for exotic species to differentiate rather than homogenize the localities analyzed. Also, the pattern of differentiation versus homogenization is strongly related to exotic species richness. When both localities have relatively few exotics, there is a clear tendency for exotics to produce biotic differentiation (JIexotic/JInative < 1). Much of this pattern seems related to the right-skewed frequency distribution of the geographic ranges of exotic species. As with native species, most exotics occur in few localities so there is a high probability that localities with low numbers of exotic species will share very few, if any, of those exotics. As exotic richness increases, the homogenizing effects become increasingly pronounced.

Cenozoic palaeogeography and the rise of modern biodiversity patterns

Abstract The steepest latitudinal and longitudinal gradients in taxonomic diversity at the present day are those associated with tropical high diversity foci. Although there has been a tendency in the past to regard these features as either evolutionary ‘cradles’ or ‘museums’ of considerable antiquity, this may not be the case. Within the marine realm, a uniform, pan-tropical fauna was progressively disrupted by a series of plate tectonic events, the most important of which were the Early Miocene ( c. 20 Ma) collisions of Africa/Arabia with Europe and Australia/New Guinea with Indonesia, and the Middle Miocene-latest Pliocene rise of the Central American Isthmus. This had the net effect of establishing two main tropical high diversity foci: the Indo-West Pacific and the Atlantic-Caribbean-East Pacific. Similar foci were also established at the same time in the terrestrial realm. Together with the physical isolation of Antarctica, these same tectonic events contributed significantly to global cooling throughout the Cenozoic Era. This in turn led to the imposition of a series of thermally defined provinces, and thus a considerable degree of biotic differentiation on a regional scale. However, something else seems to have been involved in the creation of very steep tropical diversity peaks. This could in part be a coincidental radiation of a series of unrelated taxa, or some sort of evolutionary feedback mechanism between interacting clades. Alternatively, Late Cenozoic rates of origination may have been enhanced by an external forcing mechanism such as changes in Orbital Range Dynamics.

Growth and survival of white clover (Trifolium repens) transplanted into patches of different grass species

Previous studies on Trifolium repens L. showed differentiation with respect to neighbouring plant species and local environmental conditions. In this study, we conducted a series of reciprocal transplants among and within different pastures and among neighbouring grass species (Lolium perenne L., Dactylis glomerata L., and Holcus lanatus L.). While the presence of a grass neighbour decreased survival and growth of T. repens, no evidence of differentiation by T. repens to either local environmental conditions or to neighbouring grass species was found. We suggest that T. repens, in systems like our study pastures that have small, transient grass patches, may show inconsistent and ephemeral responses to the presence of neighbouring plants, whereas in other systems with larger grass patch size and a longer period of exposure to selection processes, T. repens show fine-scale biotic differentiation to neighbouring grass species. Keywords: population differentiation, white clover, selection, microevolution, transplantation.

Neighbour relationships in grass–legume communities. IV. Fine scale biotic differentiation

Ramets of Medicago sativa L., M. Iupulina L., and Trifolium repens L. were sampled from 10-year-old fields of Bromus inermis Leyss., Phleum pratense L., and Dactylis glomerata L. The ramets were multiplied and transplanted into artificial swards in all combinations of legumes and site of origin. Differences in "performance" (in terms of dry weights and number of survivors) were shown. The most striking effect was that the number of survivors of T. repens and M. sativa (and dry weight of T. repens) was greatest when the species was transplanted back into swards of the grass species from which they had been sampled. This trend is not applicable to dry weights of M. sativa, but an alternative trend is clearly demonstrated.In a second experiment, ramets of M. sativa were sampled from 1-, 3-, and 10-year-old fields of B. inermis, P. pratense, and D. glomerata and treated as above. The most striking effect is that the performance monitored in experiment 1 may be seen developing through the 1- and 3-year-old stages, demonstrating that the microcoevolutionary processes operating within a community are rapid events.

The Growth, Distribution and Neighbour Relationships of Trifolium Repens in a Permanent Pasture: IV. Fine-Scale Biotic Differentiation

(1) Ramets of Trifolium repens were sampled from sites in a field of permanent pasture dominated by a mosaic of Lolium perenne, Holcus lanatus, Cynosurus cristatus and Agrostis tenuis. After multiplication of the ramets in a glasshouse, they were transplanted back into the original swards in all combinations of clover 'type' and site of origin. The pre-existing vegetation on the sites was either destroyed by herbicide or left as a control. (2) Clover 'types' were also transplanted into experimental sown swards of the four grass species. (3) Differences were found in aggressiveness of the grass swards and species, and between the clover 'type', and these were most clearly expressed in the growing swards. Most striking was a 'principal diagonal effect', in which each clover 'type' made most growth when transplanted back into its sward of origin-or into a pure stand of the grass that had dominated that sward. (4) This is interpreted as a micro-evolutionary esponse of clover to the diversifying selection imposed by a variety of grass neighbours, and is discussed in relation to the ecological significance of the outbreeding habit and 'Sisyphean fitness'.