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The concept of microrefugia is widely accepted to explain the post-glacial colonization of continents, which led to the present-day biotic configuration of the Earth. However, so far, microrefugia are no more than a 'theoretical necessity' without an appropriate biogeographical and ecological characterization. Here, a tentative definition and a classification of microrefugia, based on the existing literature, are proposed for discussion. A deeper biogeographical analysis of the concept is suggested using novel ecological models and methods, in order to develop new hypotheses to be tested with palaeoecological and molecular phylogenetic tools.

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The ''Great American Biotic Interchange'' (GABI) is regarded as a defining event in the biogeography of the Americas. It is hypothesized to have occurred when the Isthmus of Panama closed ca three million years ago (Ma), ending the isolation of South America and permitting the mixing of its biota with that of North America. This view of the GABI is based largely upon the animal fossil record, but recent molecular biogeographic studies of plants that show repeated instances of long-distance dispersal over major oceanic barriers suggest that perhaps the land bridge provided by the isthmus may have been less necessary for plant migration. Here we show that plants have significantly earlier divergence time estimates than animals for historical migration events across the Isthmus of Panama region. This difference in timing indicates that plants had a greater propensity for dispersal over the isthmus before its closure compared with animals. The GABI was therefore asynchronous for plants and animals, which has fundamental implications for the historical assembly of tropical biomes in the most species-rich forests on the planet.

The evolutionary origin of extant species in the Neotropics, one of the most biodiverse regions of the world, has been widely debated. One hypothesis is that neotropical species emerged primarily during the Quaternary (the last approximately 2 million years), favoured by alternating glacial/interglacial climates. An opposite view proposes an older Tertiary origin linked primarily to palaeogeographical changes. Here, a thorough review of the available literature on DNA molecular dating shows that the Tertiary-Quaternary debate no longer makes sense. Indeed, the > 1400 neotropical species whose origin has been dated have appeared in a continual fashion since the late Eocene/early Oligocene (approximately 39 million years before present) to the Quaternary. Palaeogeographical mechanisms of speciation are relatively well accepted, but diversification processes linked to climate are still controversial. These results are important to unravel both the origin of present-day biodiversity patterns at both local and global scales and the genetic and environmental mechanisms involved, which are two crucial aspects for suitable biodiversity conservation strategies.

The karstic Lake Montcortès sedimentary sequence spanning the last 1548 yr constitutes the first continuous, high-resolution, multi-proxy varved record in northern Spain. Sediments consist of biogenic varves composed of calcite, organic matter and detrital laminae and turbidite layers. Calcite layer thickness and internal sub-layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability. Higher temperatures occurred in Lake Montcortès in AD 555–738, 825–875, 1010–1322 and 1874–present. Lower temperatures and prolonged winter conditions were recorded in AD 1446–1598, 1663–1711 and 1759–1819. Extreme and multiple precipitation events dominated in AD 571–593, 848–922, 987–1086, 1168–1196, 1217–1249, 1444–1457, 1728–1741 and 1840–1875, indicating complex hydrological variability in NE Spain since AD 463. The sedimentary record of Lake Montcortès reveals a short-term relation between rainfall variability and the detrital influx, pronounced during extended periods of reduced anthropogenic influences. In pre-industrial times, during warm climate episodes, population and land use increased in the area. After the onset of the industrialization, the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio‐economic factors.

This paper reports the vegetation changes of the last millennium, as deduced from palynological analysis of a sediment core from lake Montcortès, situated around 1000 m elevation in the southern pre-Pyrenean flank. The record begins in the Middle Ages (~AD 800) and ends around AD1920, with an average resolution of about 30 years. The reconstructed vegetation sequence is complex and shows the influence of both climate and human activities in the shaping of landscape. Prefeudal times were characterized by the presence of well-developed conifer forests, which were intensely burnt at the beginning of the feudalism (AD 1000) and were replaced by cereal (rye) and hemp cultivation, as well as meadows and pastures. In the 13th century, a relatively short warming likely corresponding to the Medieval Warm Period (MWP) was inferred by the presence of a low Mediterranean scrub community today restricted below 800 m elevation. This community disappeared during the Little Ice Age (LIA) cooling in the 15th century, coinciding with a decline in human activities around the lake. Forest recovery began around AD 1500, at the beginning of the Modern period, coinciding with wetter climates. However, forests retreated again during the 17th century coinciding with a maximum in olive and hemp cultivation. This situation was reverted in post-Modern times (19th century), charactrized by an intense agricultural crisis and a significant decline of population that favored forest re-expansion. Correlations with the nearby Estanya lake, situated about 350 m below, provided a more regional picture. Besides some climatic forcing evident in both sequences, human activities seem to have the main drivers of landscape and vegetation change in the southern Pyrenean flank, in agreement with similar conclusions from other studies developed on high-mountain environments.

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