Liseth Pérez

Pollen distribution along climatic and biogeographic gradients in northern Central America

Environmental reconstructions based on fossil pollen rely on the understanding of modern pollen distribution along climatic and biogeographic gradients. This study analyses the modern pollen spectra of Central America using three basic approaches: (1) the evaluation of using modern pollen spectra to differentiate the main vegetation types of the region, (2) the usage of non-linear regression to predict individual pollen abundances as a function of climate, and (3) the construction of pollen—climate transfer functions. Standard pollen analysis was carried out on mud—water interface samples from 81 lakes in the Yucatan Peninsula and adjacent mountains of Guatemala and Mexico. Detrended correspondence and cluster analyses were used to evaluate the biogeographic patterns revealed by this modern pollen data set. Non-parametric locally weighted scatterplot smoothing (LOESS) regression was used to construct pollen—climate functional relationships. Five modern vegetation types were clearly identifiable through their associated pollen spectra: Pinus forest, Quercus forest, mountain mesophyllous forest, tropical rainforest, and tropical seasonal forest. The last group includes three subcategories (evergreen seasonal, tropical semi-deciduous, and tropical deciduous forests), which were not separable via this analysis. Precipitation and temperature trends were consistent and robust for at least 28 and 30 taxa, respectively, in the LOESS regression. While floristic patterns driven by temperature were clearly reflected by the pollen spectra, those driven by precipitation were less sharply defined. Nevertheless, pollen data from the study area offered good resolution to identify broad biogeographic patterns. Furthermore, individual taxa showed high predictability along precipitation and temperature gradients, allowing the theoretical construction of pollen—climate transfer functions. This study provided valuable tools for the interpretation of fossil pollen sequences from Central America.

Abundant assemblage of Ostracoda (Crustacea) in Mexican Miocene amber sheds light on the evolution of the brackish-water tribe Thalassocypridini

Abstract Amber inclusions of fully aquatic animals are rare, most of them isolated specimens of water-bound insect larvae. In contrast, we here describe an ample, speciose fauna of 262 fully aquatic individuals of Ostracoda (Crustacea) from Mexican amber of Early Miocene age. This fauna was trapped whilst under water swimming around trunks of resin-producing trees in a brackish lagoon. Ostracod crustaceans are typically around a millimeter in length, and are known for their mostly well-calcified bivalved carapaces that account for their unparalleled fossil record in arthropods. However, in the Chiapas amber we found representatives of the tribe Thalassocypridini, which are characterised by lightly calcified carapaces and therefore lack a substantial fossil record. Embedded in amber, this ‘drawback’ becomes a clear benefit because the unobstructed view onto the appendages otherwise hidden in the carapace allowed us to identify nine ostracod species, six of them new to science. The exceptional number of individuals permitted insights into population composition, reproduction, taphonomy and into micro-environmental parameters of the amber’s place of formation. Based on ecological data available for Recent Thalassocypridini species, we posit that this tribe reached a peak radiation in open lagoonal settings during the Miocene, and shifted towards anchialine environments by the Recent. http://zoobank.org/lsid:zoobank.org:pub:3C93A06B-F86B-404F-985D-139897F97EF3

Overview of Neotropical-Caribbean freshwater ostracode fauna (Crustacea, Ostracoda): identifying areas of endemism and assessing biogeographical affinities

Freshwater ostracodes from the Neotropical-Caribbean region are potentially excellent tools for evolutionary and paleoenvironmental studies but their use is limited, because integrated data in taxonomy, environmental, and geographical preferences of the species at large scale remain unknown. A total of 118 species were recorded in the Neotropical-Caribbean region based on existing literature and results from fieldwork. About 74% of the species are restricted to the region and most of them show limited distributional areas as a consequence of environmental heterogeneity. Based on Parsimony Analysis of Endemicity, five areas of endemism were identified: (1) southern Florida, (2) southern Mexico-northern Central America, (3) Cuba, (4) Lesser Antilles, and (5) northern Venezuela-Aruba-Curacao-Trinidad. The conservation status of these areas was revised and lake ecosystems with endemic taxa were proposed to be included in environmental protection initiatives. Biogeographical analysis showed a strong differentiation between the ostracode faunas of the Neotropical-Caribbean region and the Neotropical-Neogen region. Few exchanges of species were attributed to ecological and geographical barriers such as volcanism and irregular orography. Faunal affinities within the Neotropical-Caribbean region indicated closer relationship between southern Mexico, southern Florida and the Antilles suggesting a common biogeographical history. Middle Central America and Chiapas-Guatemala highlands were discriminated as isolated regions.

The human impact imprint on modern pollen spectra of the Maya lands

espanolPara entender el registro paleoecologico en el contexto de la ocupacion humana, es necesario examinar la distribucion del polen moderno a lo largo de gradientes climaticos y de impacto humano. Este estudio analiza las respuestas de ensambles de polen moderno de 125 muestras superficiales a la influencia humana de la region Maya, usando tres aproximaciones basicas: i) evaluacion de la habilidad de espectros de polen moderno para distinguir los principales tipos de vegetacion antropogenica y natural, ii) uso del analisis de correspondencia sin tendencia (DCA por sus siglas en ingles) para evaluar los patrones de distribucion del polen a lo largo de gradientes ambientales que incluyen la influencia humana, y iii) evaluacion de las respuestas de taxa individuales a un gradiente de influencia humana a traves del analisis de taxa indicadores de umbral. Las 125 muestras de la interfaz agua-sedimento se dividieron en cuatro grupos que corresponden a los principales tipos de vegetacion de la region Maya (bosque de pino-encino, cultivos y pastizales, bosque estacional tropical, y bosque tropical siempre verde). En terminos de las respuestas a nivel de taxon, nosotros detectamos 20 elementos asociados significativamente con el gradiente de influencia humana. Estos elementos fueron asignados a grupos de respuesta negativos (disminuciones) o positivos (incrementos) dependiendo de la direccion de respuesta. La mayoria de los elementos arboreos de bosques estacionales tropicales disminuyeron, mientras elementos no-arboreos tipicamente de vegetacion antropica aumentaron en respuesta a diferentes niveles de influencia humana. Adicionalmente, fue detectado un cambio abrupto a nivel de comunidad para un indice de influencia humana de 15. Cuando la influencia humana supera este umbral, elementos importantes de la vegetacion natural son afectados negativamente, mientras elementos oportunistas son favorecidos. En general, el estudio de la distribucion del polen a lo largo de gradientes ambientales, asi como la identificacion de taxa indicadores de impacto humano, ofrecen herramientas valiosas para interpretar los registros de polen fosil de la region Maya. EnglishTo understand human occupation in the context of paleoecological records from the Maya region, there is need to explore the distribution of modern pollen along climate and human-impact gradients. In this study, we analyze the responses of pollen assemblages from 125 surface samples to human influence in the Maya region, using three basic approaches: (i) the evaluation of using modern pollen spectra to distinguish the main anthropogenic and natural vegetation types; (ii) the usage of detrended correspondence analysis (DCA) to evaluate the distribution patterns of pollen along environmental gradients including human influence; and (iii) the evaluation of the responses of taxon-specific elements to the human-influence gradient, that expresses on the modern landscape, using threshold-indicator taxa analysis. The 125 locations where mud-water interface samples were retrieved were divided into four groups that correspond to the major vegetation types of the Maya region (coniferous and Quercus forest, croplands and pastures, tropical seasonal forest, and tropical evergreen forest). In terms of individual taxa responses, we detected 20 elements significantly related to the human-influence gradient. These were assigned to negative (decreasing) or positive (increasing) response groups depending on the response direction. Mostly arboreal elements from tropical seasonal forests decreased, while non-arboreal elements typically from anthropogenic vegetation increased in response to different levels of human influence. Also, a community-level abrupt point change is detected at a human influence index of 15. When human influence exceeds this threshold, important elements of the natural vegetation are negatively affected while opportunistic elements become favored. Overall, the study of pollen distribution along environmental gradients and the identification of taxa indicators of human impact provide valuable tools for the interpretation of fossil pollen records from the Maya region.

Holocene environmental history of tropical, mid-altitude Lake Ocotalito, México, inferred from ostracodes and non-biological indicators:

This paleolimnological study used ostracodes assemblages, element concentrations, organic and inorganic carbon content, organic C:N ratios, and stable isotope values in valves of the ostracodes Cytheridella ilosvayi as paleoindicators and is the first such investigation from a mid-elevation site in southern México. We provide a ~7600-year (9540–1970 BP) environmental history from karst Lake Ocotalito (920 m a.s.l.), which lies in the Lacandon Forest of Chiapas, México. A 5.4-m sediment core was retrieved from a water depth of 23 m. The main factor that shaped ostracodes species assemblages throughout the Holocene was lake level. A total of six species were identified, and the benthic Cytheridella ilosvayi was dominant. Less abundant species included nektobenthic taxa Cypridopsis okeechobei, Heterocypris putei, and Potamocypris sp. and benthic species Darwinula stevensoni and Pseudocandona sp. Wet conditions, high lake levels (>15 m), and low ostracodes abundances characterized the period between ~9540 and ~7820 BP. From ~7750 to 6460 BP, indicators point to stable conditions and intermediate lake levels (~15 m). Greatest ostracodes abundance and diversity occurred from ~6200 to ~4030 BP, during which mainly drier conditions were inferred, interrupted by short, humid periods. Lower abundances and low Sr and δ18O values characterized the period from ~3810 to ~1970 BP and indicate higher lake levels, that is, wetter conditions. Throughout this period, however, a slight trend toward drier conditions was observed. Comparison with paleolimnological studies in other karst lakes from the region suggests mid-altitude aquatic ecosystems may be more sensitive to climate fluctuations than lakes in the lowlands. For instance, stable isotope records from the Lake Ocotalito core display greater ranges. This, however, may simply reflect inter-lake differences in sensitivity, controlled by lake-specific hydrologic factors. The record from Lake Ocotalito fills an important gap in our knowledge of past biotic diversity, paleoclimate, and paleoenvironmental conditions in the northern Neotropics.