The Gran Chaco is a wide ecologic-geographic region comprising northern Argentina, western Paraguay, southern Bolivia and the southwestern extreme of Brazil. This region exhibits extreme ...temperatures, annually regular frosts, and sedimentary soils; it has been dramatically threatened by agriculture expansion in recent decades. Therefore, increasing knowledge of plant diversity is critical for conservation purposes. We present a Legume checklist of the Gran Chaco ecoregion including conservation status of its endemic species. Leguminosae is the third most diverse plant family in the Neotropics. Assuming a rigorous spatial definition of the Gran Chaco, we recorded 98 genera, 362 species, and 404 specific and infraspecific taxa. Endemic/typical taxa were 17%, comparable to adjacent tropical plant formations, and they were found in higher percentages in Caesalpinioideae (24%) and Cercidoideae (33%) than Papilionoideae (11%) subfamily. We also analyzed the plant diversity comparing lineages and subregions. The Gran Chaco Legumes are predominantly widespread generalists, or they belong to either Chaco sensu stricto or Neotropical Seasonally Dry Tropical Forest (SDTF) lineages. Though the Humid Chaco registered the highest species richness, Dry Chaco and Sierra Chaco, the most threatrened subregions, exhibited the highest percentages of exclusive and proper Chaco-lineage species. These results suggest that diversification of Legumes has been most relevant in Dry Chaco and Sierra Chaco, probably by their more demanding and harsh environmental conditions limiting the dispersion of generalists or intrusive-invading species. This study is paramount to reach an improved delimitation of the Gran Chaco ecoregion in transitional areas with the SDTF and Cerrado formations. Conservation status is critical in genera of high economic interest, such as Arachis, Mimosa and Prosopis. At least one third of endemic taxa exhibit a critical status of conservation or are endangered, many of them being relevant to inbreeding program or exhibiting multiple economic uses.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Aim
Factors affecting bromeliad distribution depend on the life forms of the studied species; some could grow as terrestrial, saxicolous, or epiphytic depending on the type of habitat. We analysed ...the distribution patterns of the life forms of a bromeliad species in different biogeographic domains and associated them with environmental variables and vegetation types.
Location
Chaquenian, Amazonian, and Seasonally Dry Tropical Forest domains; South America.
Taxon
The tank bromeliad Aechmea distichantha (Bromeliaceae: Bromelioideae).
Methods
We compiled records of the biogeographic distribution and the vegetation types where A. distichantha occurs based on bibliographic data, digital datasets, herbaria, and personal observations. We associated the distributional records of this species with altitude, five selected bioclimatic variables, four soil variables, and with the vegetation types where it occurs.
Results
A. distichantha has been recorded as epiphytic, terrestrial and saxicolous in all biogeographic domains but showed contrasting patterns in life form proportions among them. In the Amazonian domain, characterized by evergreen tropical and subtropical forests with high precipitation, it mainly grows as epiphytic. In the Chaquenian domain, dominated by xerophytic forests with low rainfall, high soil pH and base saturation, it mainly grows as terrestrial, whereas in the Seasonally Dry Tropical Forest domain, the three life forms were recorded in similar proportions. In azonal plant communities of all domains, it mainly grows as saxicolous.
Main Conclusions
This tank bromeliad species can thrive in sites with contrasting habitat and environmental conditions. Its ability to survive in different environments could be associated with its high frost tolerance, the presence of the CAM photosynthetic pathway, a well‐developed phytotelma, and high phenotypic plasticity. The life form prevailing in each domain is influenced by water availability (i.e., the quantity of water available during each year, the precipitation in the driest month, and the plant water supply relative to demand).
Aim To investigate the potential distribution of Seasonally Dry Tropical Forests (SDTFs) during the Quaternary climatic fluctuations; to reassess the formerly proposed ‘Pleistocenic arc hypothesis' ...(PAH); and to identify historically stable and unstable areas of SDTF distributions in the light of palaeodistribution modelling. Location SDTFs in lowland cis-Andean eastern-central South America. Methods We first developed georeferenced maps depicting the current distributional extent of SDTFs under two distinct definitions (narrow and broad). We then generated occurrence datasets, which were used with current and past bioclimatic variables to predict SDTF occurrence by implementing the maximum entropy machine-learning algorithm. We obtained historical stability maps by overlapping the presence/absence projections of each of three climatic scenarios current, 6 kyr bp during the Holocene, and 21 kyr bp during the Last Glacial Maximum (LGM). Finally, we checked the consistencies of the model prediction with qualitative comparisons of vegetation types inferred from available fossil pollen records. Results The present-day SDTF distribution is disjunct, but we provide evidence that it was even more disjunct during the LGM. Reconstructions support a progressive southward and eastward expansion of SDTFs on a continental scale since the LGM. No significant expansion of SDTFs into the Amazon Basin was detected. Areas of presumed long-term stability are identified and confirmed (the three nuclear regions, Caatinga, Misiones and Piedmont, plus the Chiquitano region), and these possibly acted as current and historical refugial areas. Main conclusions The LGM climate was probably too dry and cold to support large tracts of SDTF, which were restricted to climatically favourable areas relative to the present day (in contrast with the PAH, as it was originally conceived). Expansions of SDTFs are proposed to have occupied the southern portion of Caatinga nucleus more recently during the early-middle Holocene transition. We propose an alternative scenario amenable to further testing of an earlier SDTF expansion (either at the Lower Pleistocene or the Tertiary), followed by fragmentation in the LGM and secondary expansion in the Holocene. The stability maps were used to generate specific genetic predictions at both continental and regional scales (stable areas are expected to have higher genetic diversity and endemism levels than adjacent unstable areas) that can be used to direct field sampling to cover both stable (predicted refugia) and unstable (recently colonized) areas. Lastly, we discuss the possibility that SDTFs may experience future expansion under changing climate scenarios and that both stable and unstable areas should be prioritized by conservation initiatives.
BACKGROUND: South America is one of the most species diverse continents in the world. Within South America diversity is not distributed evenly at both local and continental scales and this has led to ...the recognition of various areas with unique species assemblages. Several schemes currently exist which divide the continental-level diversity into large species assemblages referred to as biomes. Here we review five currently available biome maps for South America, including the WWF Ecoregions, the Americas basemap, the Land Cover Map of South America, Morrone's Biogeographic regions of Latin America, and the Ecological Systems Map. The comparison is performed through a case study on the Seasonally Dry Tropical Forest (SDTF) biome using herbarium data of habitat specialist species. RESULTS: Current biome maps of South America perform poorly in depicting SDTF distribution. The poor performance of the maps can be attributed to two main factors: (1) poor spatial resolution, and (2) poor biome delimitation. Poor spatial resolution strongly limits the use of some of the maps in GIS applications, especially for areas with heterogeneous landscape such as the Andes. Whilst the Land Cover Map did not suffer from poor spatial resolution, it showed poor delimitation of biomes. The results highlight that delimiting structurally heterogeneous vegetation is difficult based on remote sensed data alone. A new refined working map of South American SDTF biome is proposed, derived using the Biome Distribution Modelling (BDM) approach where georeferenced herbarium data is used in conjunction with bioclimatic data. CONCLUSIONS: Georeferenced specimen data play potentially an important role in biome mapping. Our study shows that herbarium data could be used as a way of ground-truthing biome maps in silico. The results also illustrate that herbarium data can be used to model vegetation maps through predictive modelling. The BDM approach is a promising new method in biome mapping, and could be particularly useful for mapping poorly known, fragmented, or degraded vegetation. We wish to highlight that biome delimitation is not an exact science, and that transparency is needed on how biomes are used as study units in macroevolutionary and ecological research.
Historical climate changes have had a major effect on the distribution and evolution of plant species in the neotropics. What is more controversial is whether relatively recent Pleistocene climatic ...changes have driven speciation, or whether neotropical species diversity is more ancient. This question is addressed using evolutionary rate analysis of sequence data of nuclear ribosomal internal transcribed spacers in diverse taxa occupying neotropical seasonally dry forests, including Ruprechtia (Polygonaceae), robinioid legumes (Fabaceae), Chaetocalyx and Nissolia (Fabaceae), and Loxopterygium (Anacardiaceae). Species diversifications in these taxa occurred both during and before the Pleistocene in Central America, but were primarily pre-Pleistocene in South America. This indicates plausibility both for models that predict tropical species diversity to be recent and that invoke a role for Pleistocene climatic change, and those that consider it ancient and implicate geological factors such as the Andean orogeny and the closure of the Panama Isthmus. Cladistic vicariance analysis was attempted to identify common factors underlying evolution in these groups. In spite of the similar Mid-Miocene to Pliocene ages of the study taxa, and their high degree of endemism in the different fragments of South American dry forests, the analysis yielded equivocal, non-robust patterns of area relationships.
Unidades de vegetación de la Argentina Oyarzabal, Mariano; Clavijo, José; Oakley, Luis ...
Ecología austral,
04/2018, Letnik:
28, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Existen numerosos mapas de la vegetación espontánea de la Argentina. Sin embargo, no contamos aún con uno de todo el país con una resolución que permita distinguir unidades de vegetación dentro de ...las provincias fitogeográficas descriptas por Cabrera (1976). Analizamos las descripciones de vegetación publicadas en las últimas décadas, con especial atención sobre aquellas que produjeron mapas fisonómico-florísticos. Como resultado de ese análisis, presentamos aquí un mapa fisonómico-florístico de la vegetación espontánea de la Argentina que muestra la heterogeneidad dentro de provincias fitogeográficas. El mapa tiene 50 unidades de vegetación como subdivisiones de las provincias fitogeográficas y el ecotono descritos con anterioridad, acompañadas de una breve descripción de la fisonomía y composición florística. Proponemos una nomenclatura de las unidades de vegetación según el tipo de vegetación espontánea dominante y especies características, y presentamos material cartográfico electrónico.
Until the beginning of the twentieth century there were extensive subtropical seasonal thorny forests surrounding the Pampas grasslands of Argentina, known as the ‘Espinal'. In central Argentina ...there still exist relicts of the Espinal, belonging to the ‘Entrerrianense District'. These forests were never described or analyzed in detail. In 2004 we studied 10 randomly located plots of 50 × 2 m. All individuals and stems of woody species were counted and their diameters at breast height (DBH) were measured; individuals with <1 cm DBH were considered juveniles. We recorded 2,300 woody individuals/ha corresponding to 12 species. The more constant species are the palm Trithrinax campestris (100%), Celtis tala (90%), Prosopis alba and Celtis pallida (both 50%). The plots are relatively homogeneous, but once classified with cluster analysis two groups are formed according to the relative abundance of C. tala and T. campestris; the latter species is more frequent in more open or fire-disturbed habitats. The results of Canonical Analysis of Principal coordinates are in agreement with the classification. We postulate that the differences between both groups are caused by a differential degree of disturbance (probably caused by fires). Both dominant species show abundant juveniles, and the invasion by exotic woody species is limited. These forest relicts are among the last remnants of the massive expansions of forests in central Argentina. Besides their historical value, an urgent call is made for their preservation, sustainable use and defence from biological invasions.
Introducción y Objetivos: Ruprechtia apetala (Polygonaceae) es una especie que presenta una gran variabilidad morfológica entre individuos a lo largo de su rango de distribución. El presente estudio ...tiene como objetivo evaluar dicha variabilidad morfológica dentro del territorio argentino.
M&M: se colectaron 42 individuos en seis provincias argentinas correspondientes a las regiones Chaqueña serrana, Selva Pedemontana y a la zona de transición entre ellas. Fueron analizados numerosos caracteres morfológicos, tanto vegetativos como reproductivos. Se realizaron Análisis de Componentes Principales y de Conglomerados para detectar morfogrupos; estos últimos se evaluaron mediante análisis univariados (Prueba de Kruskal-Wallis y descripción de clusters mediante R) y multivariados (ANOSIM y PERMANOVA), para evaluar posibles diferencias intraespecíficas significativas. Adicionalmente, se confeccionó un mapa de distribución biogeográfica de los individuos.
Resultados: a partir del análisis multivariado se detectaron dos grupos morfológicos, principalmente a niveles foliar y de hábito de crecimiento. Los Análisis ANOSIM y PERMANOVA muestran que existe una diferencia global significativa entre ambos grupos (p-valor < 0,05); no obstante, los estadísticos correspondientes indican una elevada similitud entre ellos. Adicionalmente, mediante la descripción de cada conglomerado, se corroboró que no existen estados de caracteres mutuamente excluyentes para uno u otro grupo.
Conclusiones: La variabilidad morfológica encontrada entre ejemplares de distintas regiones biogeográficas, y la no exclusividad de caracteres morfológicos para cada grupo particular, permite postular la existencia de ecotipos en la especie.
Aim: To investigate the potential distribution of Seasonally Dry Tropical Forests (SDTFs) during the Quaternary climatic fluctuations; to reassess the formerly proposed 'Pleistocenic arc hypothesis' ...(PAH); and to identify historically stable and unstable areas of SDTF distributions in the light of palaeodistribution modelling. Location: SDTFs in lowland cis-Andean eastern-central South America. Methods: We first developed georeferenced maps depicting the current distributional extent of SDTFs under two distinct definitions (narrow and broad). We then generated occurrence datasets, which were used with current and past bioclimatic variables to predict SDTF occurrence by implementing the maximum entropy machine-learning algorithm. We obtained historical stability maps by overlapping the presence/absence projections of each of three climatic scenarios current, 6 kyr вр during the Holocene, and 21 kyr вр during the Last Glacial Maximum (LGM). Finally, we checked the consistencies of the model prediction with qualitative comparisons of vegetation types inferred from available fossil pollen records. Results: The present-day SDTF distribution is disjunct, but we provide evidence that it was even more disjunct during the LGM. Reconstructions support a progressive southward and eastward expansion of SDTFs on a continental scale since the LGM. No significant expansion of SDTFs into the Amazon Basin was detected. Areas of presumed long-term stability are identified and confirmed (the three nuclear regions, Caatinga, Misiones and Piedmont, plus the Chiquitano region), and these possibly acted as current and historical refugial areas. Main conclusions: The LGM climate was probably too dry and cold to support large tracts of SDTF, which were restricted to climatically favourable areas relative to the present day (in contrast with the PAH, as it was originally conceived). Expansions of SDTFs are proposed to have occupied the southern portion of Caatinga nucleus more recently during the early-middle Holocene transition. We propose an alternative scenario amenable to further testing of an earlier SDTF expansion (either at the Lower Pleistocene or the Tertiary), followed by fragmentation in the LGM and secondary expansion in the Holocene. The stability maps were used to generate specific genetic predictions at both continental and regional scales (stable areas are expected to have higher genetic diversity and endemism levels than adjacent unstable areas) that can be used to direct field sampling to cover both stable (predicted refugia) and unstable (recently colonized) areas. Lastly, we discuss the possibility that SDTFs may experience future expansion under changing climate scenarios and that both stable and unstable areas should be prioritized by conservation initiatives.
This study provides a preliminary phylogeny of the
Celtis
species from the neotropical region with emphasis on the South American species. We analyzed 19 taxa using the plastid
psbA
-
trn
H and ...nuclear ITS 4-5, and
FA16180
b markers. The sequence data were analyzed using maximum parsimony, maximum likelihood, and Bayesian inference. The South American species were highly supported as monophyletic, while the North American species were recovered as paraphyletic. The endocarp morphology corroborated the lineages within the molecular phylogeny and helps to differentiate the species, to recognize a new species
Celtis serratissima
, and to reestablish two previously known species,
Celtis clausseniana
(Wedd.) Miq. and
Celtis spinosissima
(Wedd.) Miq. These three species emerged among one of the three lineages of the tropical South American species.
Celtis serratissima
is thus described, illustrated, and compared to its most closely related species.
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