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Wide Geographic Range (wide + geographic_range)
Selected AbstractsFactors Affecting Population Assessments of Desert TortoisesCONSERVATION BIOLOGY, Issue 5 2000Jerome E. Freilich With a wide geographic range and more living individuals than any other listed land animal, biologists have needed to detect population trends against a "noisy" background of strong annual changes. We obtained annual population estimates of desert tortoises over 6 consecutive years at a 2.59-km2 plot in Joshua Tree National Park, California. Our estimates, based on weekly spring surveys, varied substantially, particularly between wet and dry years. Concurrently, we followed 10 radiotagged animals for 3 years to corroborate the surveys. Population density was determined separately for each year and for all years combined. Our best population estimate was an average of 67 adult tortoises, three times more than the density reported in a 1978 survey of the same site. Annual mortality was low ( <10%), and the animals showed extreme site fidelity. Apparent changes in population size were most strongly related to the animals' varying susceptibility to capture. In dry years, home ranges decreased, captures decreased, and effort required to find each tortoise nearly doubled. Our data confirm that tortoises are likely to be undercounted during dry years and call into question earlier studies conducted during droughts. Resumen: Las tortugas del desierto han sido tema de controversia desde que fueron enlistadas como amenazadas en 1990. Con un amplio rango de distribución geográfica y más individuos vivos que cualquier otro animal terrestre enlistado, los biólogos han necesitado detectar tendencias poblacionales contra un trasfondo "ruidoso" de cambios anuales fuertes. Obtuvimos estimaciones de la población anual de tortugas del desierto por seis años consecutivos en un cuadrante de 2.59 Km2 en el Parque Nacional Joshua Tree de California. Nuestras estimaciones, basadas en sondeos semanales de primavera, variaron sustancialmente, particularmente al comparar años lluviosos con años secos. Al mismo tiempo, monitoreamos por tres años a 10 animales marcados con radiotransmisores para corroborar los sondeos. La densidad poblacional estuvo determinada por separado para cada año y para todos los años combinados. Nuestras mejores estimaciones de densidad poblacional fueron en promedio de 67 adultos, tres veces más que la densidad reportada en un sondeo de 1978 en el mismo sitio. La mortalidad anual fue baja ( <10%) y los animales mostraron una fidelidad extrema por el sitio. Los cambios aparentes en el tamaño poblacional estuvieron más fuertemente relacionados con la variación en la susceptibilidad de captura de los animales. En años secos, el rango de hogar disminuyó, las capturas disminuyeron, y el esfuerzo requerido para encontrar cada tortuga fue de casi el doble. Nuestros datos confirman que las tortugas son probablemente mal contadas ( menos) durante los años de seca y ponen en duda estudios previos realizados durante secas. [source] Adaptive advantages of myrmecochory: the predator-avoidance hypothesis tested over a wide geographic rangeECOGRAPHY, Issue 5 2005Antonio J. Manzaneda The predator-avoidance hypothesis states that once released from the parent plant, myrmecochorous seeds are rapidly taken by ants to their nests, where they are protected from predators. Previous studies conducted to test this hypothesis have frequently neglected two major aspects necessary for its verification: 1) the influence of processes acting after the seed release and 2) the spatial evenness of such processes. Thus, large-scale variations in the mechanisms acting beyond seed release, and possibly influencing seed escape from predators, remain poorly documented. Here, we present the results of a post-dispersal seed-removal experiment on the myrmecochorous herb Helleborus foetidus, aimed at verifing the predator-avoidance hypothesis by considering two key post-release aspects of seed fate: seed destination (dispersed or nondispersed) and seed burial (buried or not buried). Experiments were performed in four different regions in the Iberian Peninsula. After three days of exposure of seeds to the main predator (fieldmice Apodemus sylvaticus), ca 30% of the seeds were removed. Seed destination affected the proportion of seeds escaping predation, but the sign, magnitude and statistical significance of the effect varied among the geographical regions. In the southern region (Cazorla), seeds dispersed in ant nests or intermediate destinations suffered scarcely any predation, but seeds under reproductive-age plants experienced losses ca 50%. Conversely, in the northern region (Caurel), seeds in nests suffered significantly greater losses than seeds under plants or intermediate destinations, suggesting that nests were especially unsafe destinations. Seed burial had a strong impact on seed escape from predators, and its effect was highly consistent among geographical regions. In view of the consistency of its effect at different spatial scales, seed burial was a more general mechanism for predation avoidance than seed relocation to ant nests, which was habitat- and/or ant-species-dependent. Our results thus only partially support the predator-avoidance hypothesis for the evolution of myrmecochory. [source] EVALUATION OF ELEVATED PLOIDY AND ASEXUAL REPRODUCTION AS ALTERNATIVE EXPLANATIONS FOR GEOGRAPHIC PARTHENOGENESIS IN EUCYPRIS VIRENS OSTRACODSEVOLUTION, Issue 4 2010Sofia Adolfsson Transitions from sexual to asexual reproduction are often coupled with elevations in ploidy. As a consequence, the importance of ploidy per se for the maintenance and spread of asexual populations is unclear. To examine the effects of ploidy and asexual reproduction as independent determinants of the success of asexual lineages, we sampled diploid sexual, diploid asexual, and triploid asexual Eucypris virens ostracods across a European wide range. Applying nuclear and mitochondrial markers, we found that E. virens consists of genetically highly differentiated diploid sexual populations, to the extent that these sexual clades could be considered as cryptic species. All sexual populations were found in southern Europe and North Africa and we found that both diploid asexual and triploid asexual lineages have originated multiple times from several sexual lineages. Therefore, the asexual lineages show a wide variety of genetic backgrounds and very strong population genetic structure across the wide geographic range. Finally, we found that triploid, but not diploid, asexual clones dominate habitats in northern Europe. The limited distribution of diploid asexual lineages, despite their shared ancestry with triploid asexual lineages, strongly suggests that the wider geographic distribution of triploids is due to elevated ploidy rather than to asexuality. [source] A quantitative review comparing the yield of switchgrass in monocultures and mixtures in relation to climate and management factorsGCB BIOENERGY, Issue 1 2010DAN WANG Abstract Switchgrass (Panicum virgatum L.), a US Department of Energy model species, is widely considered for US biomass energy production. While previous studies have demonstrated the effect of climate and management factors on biomass yield and chemical characteristics of switchgrass monocultures, information is lacking on the yield of switchgrass grown in combination with other species for biomass energy. Therefore, the objective of this quantitative review is to compare the effect of climate and management factors on the yield of switchgrass monocultures, as well as on mixtures of switchgrass, and other species. We examined all peer-reviewed articles describing productivity of switchgrass and extracted dry matter yields, stand age, nitrogen fertilization (N), temperature (growing degree days), and precipitation/irrigation. Switchgrass yield was greater when grown in monocultures (10.9 t ha,1, n=324) than when grown in mixtures (4.4 t ha,1, n=85); yield in monocultures was also greater than the total yield of all species in the mixtures (6.9 t ha,1, n=90). The presence of legume species in mixtures increased switchgrass yield from 3.1 t ha,1 (n=65) to 8.9 t ha,1 (n=20). Total yield of switchgrass-dominated mixtures with legumes reached 9.9 t ha,1 (n=25), which was not significantly different from the monoculture yield. The results demonstrated the potential of switchgrass for use as a biomass energy crop in both monocultures and mixtures across a wide geographic range. Monocultures, but not mixtures, showed a significant positive response to N and precipitation. The response to N for monocultures was consistent for newly established (stand age <3 years) and mature stands (stand age ,3 years) and for lowland and upland ecotypes. In conclusion, these results suggest that fertilization with N will increase yield in monocultures, but not mixtures. For monocultures, N treatment need not be changed based on ecotype and stand age; and for mixtures, legumes should be included as an alternative N source. [source] Genome-wide single nucleotide polymorphisms reveal population history and adaptive divergence in wild guppiesMOLECULAR ECOLOGY, Issue 5 2010EVA-MARIA WILLING Abstract Adaptation of guppies (Poecilia reticulata) to contrasting upland and lowland habitats has been extensively studied with respect to behaviour, morphology and life history traits. Yet population history has not been studied at the whole-genome level. Although single nucleotide polymorphisms (SNPs) are the most abundant form of variation in many genomes and consequently very informative for a genome-wide picture of standing natural variation in populations, genome-wide SNP data are rarely available for wild vertebrates. Here we use genetically mapped SNP markers to comprehensively survey genetic variation within and among naturally occurring guppy populations from a wide geographic range in Trinidad and Venezuela. Results from three different clustering methods, Neighbor-net, principal component analysis (PCA) and Bayesian analysis show that the population substructure agrees with geographic separation and largely with previously hypothesized patterns of historical colonization. Within major drainages (Caroni, Oropouche and Northern), populations are genetically similar, but those in different geographic regions are highly divergent from one another, with some indications of ancient shared polymorphisms. Clear genomic signatures of a previous introduction experiment were seen, and we detected additional potential admixture events. Headwater populations were significantly less heterozygous than downstream populations. Pairwise FST values revealed marked differences in allele frequencies among populations from different regions, and also among populations within the same region. FST outlier methods indicated some regions of the genome as being under directional selection. Overall, this study demonstrates the power of a genome-wide SNP data set to inform for studies on natural variation, adaptation and evolution of wild populations [source] Introgressive hybridization in southern African baboons shapes patterns of mtDNA variationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010C. Keller Abstract Species, as main evolutionary units have long been considered to be morphological entities with limited hybridization potential. The occurrence of taxa which maintain morphological distinctness despite extensive hybridization is an interesting phenomenon. To understand the evolution of these taxa, descriptions of contemporary morphological and genetic variation are essential, also to reconstruct sound phylogenies. Baboons, with their wide geographic range, variant morphotypes, and extensive hybridization offer an intriguing model for those studies. We focus on the complex situation in southern Africa that, in contrast to east Africa, has been neglected in terms of baboon hybridization history. We aim to clarify the distribution and identify possible overlapping zones between different, previously described mitochondrial (mt) DNA clades of baboons that do not match with the ranges of traditionally recognized species. On the basis of the widespread sampling and mitochondrial cytochrome b gene sequencing, we constructed a phylogenetic tree that separates representatives of the two southern African baboon species, yellow and chacma baboons, into six clades: southern, northern and eastern chacmas, Kinda baboons and southern and Luangwa yellow baboons. The ranges of the chacma clades come into close contact or overlap in two regions in the Republic of South Africa and Namibia. Our phylogenetic reconstruction reveals mitochondrial paraphyly for chacma and yellow baboons, which is probably caused by introgressive hybridization and subsequent nuclear swamping, whereby males of the chacma morphotype population from the south invaded the yellow morphotype population in the north bringing their morphotype into a population that maintained its yellow baboon mtDNA. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] | ||||||||||