Number Of Dispersal Events Research Articles

Landscape Heterogeneity and Environmental Dynamics Improve Predictions of Establishment Success of Colonising Small Founding Populations.

In long-distance dispersal events, colonising species typically begin with a small number of founding individuals. A growing body of research suggests that establishment success of small founding populations can be determined by the context of the colonisation event and the new environment. Here, we illuminate the importance of these sources of context dependence. Using a spatially explicit, temporally dynamic, mechanistic, individual-based simulator of a model amphibian species, the cane toad (Rhinella marina), we simulated colonisation scenarios to investigate how (1) the number of founding individuals, (2) the number of dispersal events, (3) landscape's spatial composition and configuration of habitats ('spatially heterogeneous landscapes') and (4) the timing of arrival with regards to dynamic environmental conditions ('dynamic environmental conditions') influence the establishment success of small founding populations. We analysed the dynamic effects of these predictors on establishment success using running-window logistic regression models. We showed establishment success increases with the number of founding individuals, whereas the number of dispersal events had a weak effect. At ≥ 20 founding individuals, propagule size swamps the effects of other factors, to whereby establishment success is near-certain (≥ 90%). But below this level, confidence in establishment success dramatically decreases as number of founding individuals decreases. At low numbers of founding individuals, the prominent predictors are landscape spatial heterogeneity and dynamic environmental conditions. For instance, compared to the annual mean, founding populations with ≤ 5 individuals have up to 18% higher establishment success when they arrive in 'packed' landscapes with relatively limited and clustered essential habitats and right before the breeding season. Accounting for landscape spatial heterogeneity and dynamic environmental conditions is integral in understanding and predicting population establishment and species colonisation. This additional complexity is necessary for advancing biogeographical theory and its application, such as in guiding species reintroduction efforts and invasive alien species management.

Model misspecification misleads inference of the spatial dynamics of disease outbreaks

Epidemiology has been transformed by the advent of Bayesian phylodynamic models that allow researchers to infer the geographic history of pathogen dispersal over a set of discrete geographic areas [1, 2]. These models provide powerful tools for understanding the spatial dynamics of disease outbreaks, but contain many parameters that are inferred from minimal geographic information (i.e., the single area in which each pathogen was sampled). Consequently, inferences under these models are inherently sensitive to our prior assumptions about the model parameters. Here, we demonstrate that the default priors used in empirical phylodynamic studies make strong and biologically unrealistic assumptions about the underlying geographic process. We provide empirical evidence that these unrealistic priors strongly (and adversely) impact commonly reported aspects of epidemiological studies, including: 1) the relative rates of dispersal between areas; 2) the importance of dispersal routes for the spread of pathogens among areas; 3) the number of dispersal events between areas, and; 4) the ancestral area in which a given outbreak originated. We offer strategies to avoid these problems, and develop tools to help researchers specify more biologically reasonable prior models that will realize the full potential of phylodynamic methods to elucidate pathogen biology and, ultimately, inform surveillance and monitoring policies to mitigate the impacts of disease outbreaks.

Testing the causes of richness patterns in the paleotropics: time and diversification in cycads (Cycadaceae)

The paleotropics harbor many biodiversity hotspots and show many different species richness patterns. However, it remains unclear which factors are the most important in directly shaping richness patterns among regions in the paleotropics (i.e. diversification rates, colonization times, and dispersal frequency). Here we used Cycadaceae as a model system to test the causes of regional richness patterns in the paleotropics. Specifically, we tested the roles of dispersal frequency, colonization time, diversification rates, and their combined role in explaining richness patterns among regions. We generated a well‐sampled, time‐calibrated phylogeny and then used this to estimate dispersal events, colonization times, and diversification rates. Richness patterns were significantly associated with the timing of the first colonization of each region and were best explained by the combined effects of colonization time and diversification rates. The number of dispersal events into each region and the diversification rates of species in each region were not significantly related to richness. Ancestral‐area reconstructions showed frequent migrations across Wallace's line, with a higher diversification rate east of Wallace's line than west of it. Overall, our study shows that colonization time can be an important factor for explaining regional richness patterns in the paleotropics.

The abrupt climate change at the Eocene–Oligocene boundary and the emergence of South-East Asia triggered the spread of sapindaceous lineages

Paleoclimatic data indicate that an abrupt climate change occurred at the Eocene-Oligocene (E-O) boundary affecting the distribution of tropical forests on Earth. The same period has seen the emergence of South-East (SE) Asia, caused by the collision of the Eurasian and Australian plates. How the combination of these climatic and geomorphological factors affected the spatio-temporal history of angiosperms is little known. This topic is investigated by using the worldwide sapindaceous clade as a case study. Analyses of divergence time inference, diversification and biogeography (constrained by paleogeography) are applied to a combined plastid and nuclear DNA sequence data set. Biogeographical and diversification analyses are performed over a set of trees to take phylogenetic and dating uncertainty into account. Results are analysed in the context of past climatic fluctuations. An increase in the number of dispersal events at the E-O boundary is recorded, which intensified during the Miocene. This pattern is associated with a higher rate in the emergence of new genera. These results are discussed in light of the geomorphological importance of SE Asia, which acted as a tropical bridge allowing multiple contacts between areas and additional speciation across landmasses derived from Laurasia and Gondwana. This study demonstrates the importance of the combined effect of geomorphological (the emergence of most islands in SE Asia approx. 30 million years ago) and climatic (the dramatic E-O climate change that shifted the tropical belt and reduced sea levels) factors in shaping species distribution within the sapindaceous clade.

Reconstructing the biogeographical history of two plant genera with different dispersion capabilities

AbstractAim The pappus is one of the most distinctive features of the genera belonging to the sunflower family, and is an efficient mechanism for dispersion by wind. The pappose Holocheilus (seven species) and the non‐pappose Panphalea (nine species) are two genera of the monophyletic subtribe Nassauviinae (Asteraceae, Mutisieae), which overlap in their areas of distribution. This paper aims to reconstruct the biogeographical histories that shaped the distribution of these two genera, which are phylogenetically and geographically related, but differ in their means of dispersion. Our initial expectation was that the dispersion capability of the pappus should be reflected in more dispersal events in Holocheilus than in Panphalea.Location South‐eastern Brazil, Paraguay, Uruguay and Argentina.Methods Morphological data were acquired from the literature and by analysis of specimens. Two cladistic analyses, one for Holocheilus and one for Panphalea, were based on morphological characters, and data matrices were analysed with the Fitch parsimony algorithm of paup. The ancestral distributions were reconstructed using diva ver. 1.1 according to the dispersal–vicariance optimization method.Results The Paranense‐fields were identified as the most likely ancestral area of Holocheilus and Panphalea. Biogeographical reconstruction of Holocheilus shows several dispersal events from the Paranense‐fields: two ancestral dispersal events to the Yungas, followed by vicariance events (Paranense‐fields/Yungas) and numerous terminal dispersals to the surrounding areas such as Chacoan, Pampean and Espinal. diva reconstruction of Panphalea distribution also shows frequent terminal dispersals, with no vicariant events, from the Paranense‐fields to the other areas: (1) to Espinal, Pampean‐Uruguayan, Pampean‐oriental; (2) to Paranense‐hills; (3) to Pampean‐Uruguayan; and (4) to Paranense‐pine lands.Main conclusions In the past, both genera probably originated in the Paranense‐fields area, which was subject to the dry and humid cycles of the Quaternary glaciations. Dispersal was the process that predominantly shaped the distribution of Panphalea and Holocheilus, with approximately the same number of dispersal events in both genera, despite differing ranges of dispersion. The main barriers to dispersal were the dry Cerrado and Chaco, the latter promoting vicariance in Holocheilus. The lack of a pappus in Panphalea was a limitation for its dispersion compared with Holocheilus.

Reading the history of a hybrid fish complex from its molecular record

Squalius alburnoides is a widely distributed intergeneric hybrid complex with fish of both sexes, varying ploidy levels and proportions of the parental genomes. Its dispersal routes were here delineated and framed by the reconstruction of the phylogeny and phylogeography of other Squalius with which it hybridizes, based on the available data on the paleohydrographical history of the Iberian Peninsula. Results based on sequences of cytochrome b and beta-actin genes showed that: proto- Squalius pyrenaicus originated at least five species as it dispersed throughout the Iberian Peninsula in the Mio-Pliocene; the S. alburnoides complex likely had a single origin in the bulk of Iberia, in the Upper Tagus/Guadiana area, when hydrographical rearrangements allowed the contact between its ancestors (around 700,000 years ago); interspecific crosses allowed the introgression of mitochondrial and nuclear genes of S. alburnoides in allopatric species/populations of other Squalius and vice-versa; and reconstituted S. alburnoides non-hybrid males may contribute to the replacement of the typical mtDNA of the complex (in the populations where they occur, crosses with females of other Squalius seem to have been especially frequent). A number of dispersal events and colonization routes are proposed.

Spiny Norman in the Garden of Eden? Dispersal and early biogeography of Placentalia

The persistent finding of clades endemic to the southern continents (Afrotheria and Xenarthra) near the base of the placental mammal tree has led molecular phylogeneticists to suggest an origin of Placentalia, the crown group of Eutheria, somewhere in the southern continents. Basal splits within the Placentalia have then been associated with vicariance due to the breakup of Gondwana. Southern-origin scenarios suffer from several problems. First, the place of origin of Placentalia cannot be reconstructed using phylogenetic reasoning without reference to outgroups. When available outgroups are considered, a Laurasian origin is most parsimonious. Second, a model of pure vicariance would require that basal placental splits occurred not with the breakup of Gondwana, but of Pangea in the Late Triassic—Early Jurassic. This event long preceded even the oldest molecular divergence estimates for the Placentalia and was coeval only with the earliest mammals in the fossil record. Third, a problem with the number of dispersal events that would be required emerges under different southern-origin scenarios. In considering the geographic distribution of the major placental clades at their first appearance (mostly Early Cenozoic), it becomes clear that a Laurasian center of origin would require fewer dispersal events. Southern-origin models would require at least twice the number of dispersal events in comparison with a model of Laurasian origins. This number of required dispersal events increases if extinct groups of placental mammals are also considered. Results are similar assuming a morphology-based phylogeny. These facts, along with earlier findings speaking against a major placental radiation deep in the Cretaceous without leaving fossil evidence, suggest an origin of Placentalia somewhere in Laurasia with few supraordinal splits occurring before the last 5–10 million years of the Cretaceous.

Molecular phylogeny of the antitropical genus Pseudolabrus (Perciformes: Labridae): evidence for a Southern Hemisphere origin

The genus Pseudolabrus comprises 11 species of marine nearshore fishes which are antitropically distributed: two species occur in East Asia, the remaining nine species being distributed in the Southern Hemisphere, mainly in the temperate Pacific. The distributions of their closely allied genera, collectively called “pseudolabrines” are, however, restricted to the Australia-New Zealand region. The molecular phylogeny of six of the 11 Pseudolabrus species from both Hemispheres and four of the five other pseudolabrine genera was reconstructed from nucleotide sequence data from mitochondrial DNA 12S rRNA, tRNA Val, and 16S rRNA genes. Both parsimony and Bayesian analyses were performed. Results are not consistent with a previous phylogenetic hypothesis based on osteological data, particularly in the relationship between Pseudolabrus and Notolabrus, indicating a probable need for reviewing the status of Notolabrus (or the delimitations of both Pseudolabrus and Notolabrus). The two Northern Hemisphere species of Pseudolabrus were monophyletic and nested deep into the clade of the Southern Hemisphere pseudolabrines, which indicates that both pseudolabrines and Pseudolabrus originated in the Southern Hemisphere. A dispersal rather than vicariance explanation for the antitropical distribution of Pseudolabrus is more parsimonious given the number of dispersal events, extinctions, and evolutionary adaptations required under the phylogeny. Based on molecular clock calibrations, the transequatorial divergence was suggested to be early to mid Pliocene at the earliest.