Geographically peripheral populations are believed to be particularly important in a species' response to environmental change and for the conservation of intraspecific genetic diversity. It is expected that as a species' range limits are approached, productivity and reproduction will decline and populations will become less abundant and more isolated. Decreased genetic variability and increased genetic divergence of peripheral populations is predicted based on these patterns. Cirsium heterophyllum reaches a southern geographical limit in the UK, C. acaule and C. eriophorum reach a northern limit and C. arvense occurs throughout the UK. These species have been used to determine whether contemporary patterns of distribution, productivity and reproductive potential across a species' UK latitudinal range are reflected in the predicted patterns of population genetic structure (assessed using microsatellite markers). Population frequency declines approaching the periphery of Cirsium acaule and C. heterophyllum. A decline in abundance was found in C. heterophyllum only. Community surveys suggest that peripheral populations do not occur in atypical habitat. There is no latitudinal variation in morphological characters across the species range, whereas reproductive potential declines approaching the periphery of the species that reach a latitudinal limit in the UK. Population genetic analysis revealed a decline in genetic variation toward the latitudinal limit of C. acaule. This pattern is absent in C. heterophyllum despite a marked decline in seed production and increase in population - . isolation approaching its periphery. C. heterophyllum exhibits almost randomised geographical structure of genetic variation. The lack of agreement between patterns of reproductive potential and population frequency and population genetic structure suggests that contemporary patterns of population distribution and reproduction may be inadequate for indicating patterns of population genetic structure within a species. Interspecific differences in post-glacial history may be important in explaining this disparity.

<p>Many endotherms use torpor on a seasonal or daily basis to conserve metabolic resources during difficult conditions, but the capacity to do so has never been recognized as varying intraspecifically. I hypothesized that populations that are exposed to prolonged cold, snow, or scarcity of food resources relative to other conspecifics may express torpor despite the fact that other conspecifics may not use, or even be capable of, torpor. I studied thermoregulation of black-tailed prairie dogs (<I>Cynomys ludovicianus</I>) and Ords kangaroo rats (<I>Dipodomys ordii</I>) at the extreme northernmost periphery of each species range to determine whether there is evidence for geographic variation in torpor patterns.</p><p>Contrary to previous studies of black-tailed prairie dogs near the centre of the species range, I found that northern prairie dogs hibernate during winter, spending up to 95 days per year in torpor. Synchrony of body temperature patterns of some individuals suggests that northern prairie dogs hibernate communally. Similarly, in contrast to previous studies of kangaroo rats in more southern localities, I found that northern Ords kangaroo rats use daily torpor during winter, entering torpor on up to 70 days per year. Kangaroo rats that use deep torpor exhibit comparable survival and pre-winter body mass, but poorer spring body condition, than kangaroo rats that do not use deep torpor. I reported the details of my procedures for studying thermoregulation of small mammals in the wild, to encourage comparable studies that would provide additional insights on intraspecific variation in torpor patterns. My findings are the first to demonstrate that the capacity for torpor varies predictably on a geographic basis.</p>

<p>Many endotherms use torpor on a seasonal or daily basis to conserve metabolic resources during difficult conditions, but the capacity to do so has never been recognized as varying intraspecifically. I hypothesized that populations that are exposed to prolonged cold, snow, or scarcity of food resources relative to other conspecifics may express torpor despite the fact that other conspecifics may not use, or even be capable of, torpor. I studied thermoregulation of black-tailed prairie dogs (<I>Cynomys ludovicianus</I>) and Ords kangaroo rats (<I>Dipodomys ordii</I>) at the extreme northernmost periphery of each species range to determine whether there is evidence for geographic variation in torpor patterns.</p><p>Contrary to previous studies of black-tailed prairie dogs near the centre of the species range, I found that northern prairie dogs hibernate during winter, spending up to 95 days per year in torpor. Synchrony of body temperature patterns of some individuals suggests that northern prairie dogs hibernate communally. Similarly, in contrast to previous studies of kangaroo rats in more southern localities, I found that northern Ords kangaroo rats use daily torpor during winter, entering torpor on up to 70 days per year. Kangaroo rats that use deep torpor exhibit comparable survival and pre-winter body mass, but poorer spring body condition, than kangaroo rats that do not use deep torpor. I reported the details of my procedures for studying thermoregulation of small mammals in the wild, to encourage comparable studies that would provide additional insights on intraspecific variation in torpor patterns. My findings are the first to demonstrate that the capacity for torpor varies predictably on a geographic basis.</p>

The sand lizard (Lacerta agilis) reaches the northern periphery of its distribution in south-central Sweden, where small, isolated relict populations occur in pine heath forests on sandy sediments. Modern forestry and fire suppression have reduced the amount of suitable open habitat for the species in this area and seem to be important for its decline. Main objectives of this thesis were to evaluate the efficiency of different management strategies, and if the sand lizard can function as an umbrella species for biodiversity conservation. Over a 16-year period, the estimated annual numbers of adult females in each of two study populations fluctuated between 23 and 3. Simulations of stochastic future population growth showed that the risk of extinction was highly dependent on population growth rate, which in turn was strongly affected by juvenile survival as indicated by elasticity analysis. Simulations of population growth for 50 years showed that the quasi-extinction risk (threshold ≤ 10 females) was &gt; 56% for patches ≤ 1 ha; which is the observed average size of suitable habitat for inhabited patches during a 10-year period. In managed metapopulation networks with highly co-fluctuating local populations, among-population dispersal was not important to reduce extinction risks over a 50-year horizon. In the field the preferred microhabitat of sand lizards was successfully restored using tree felling and patch-soil scarification. The lizards gradually colonized the restored patches, and 16 years after restoration, sand lizards where mainly found there. Pine-heath area, and patch area within individual pine heaths, were of major importance for long-term population persistence at regional and landscape scales, respectively. Analyses of nested species subsets and an umbrella index suggest that the sand lizard can be a useful cross-taxonomic umbrella species on both scales for other red-listed species.

Tesi realitzada al Instituto Pirenaico de Ecología (CSIC) / Widespread species have traditionally received much less attention than rare and endemic ones. However, they are crucial in macroecological patterns and in ecosystem structure and functioning. Thus, understanding the characteristics that allow widespread organisms to extend over large areas has a high interest from both theoretical and applied perspectives. One of the most frequent hypotheses to explain the success of widespread plants is that they show much wider ecological niches, and thus a high life-history and demographic variability. However, studies are often very specific and carried out over small spatio-temporal scales, which hinders a general understanding of intraspecific variation in widespread taxa. In this thesis, we span a large spatio-temporal scale and a large environmental gradient to analyze the magnitude and the possible causes of natural variation in the in the range centre and the northern periphery of the widespread herb Plantago coronopus. More precisely, we analyze variability in population dynamics, life-history traits, and genetic diversity in up to 22 populations in Europe and North Africa. We aim to explore the relation of such variability with the position of populations within the species’ range, since peripheral populations are traditionally expected to show a lower and more variable performance with respect to central populations. Additionally, we aim to analyze the effects of the most relevant environmental factors in population and individual performance at different spatial scales. In the first chapter, we found higher values in central populations in some vital rates, such as fecundity and growth, but recruitment and density were higher in northern peripheral populations, and there were no clear differences between regions in temporal variability of vital rates. Differences in population performance across the species’ range seemed to be correlated with local precipitation and intraspecific competition. In the second chapter, differences in mean values and variability of vital rates between central and peripheral areas led to no differences in stochastic population growth rates. In addition, recruitment was the most influential vital rate for population growth rates at different spatial scales, and we found the same pattern of differentiation in population dynamics in response to environmental conditions within central and peripheral regions. In the third chapter, we reported high variation among populations in seed traits along a steep environmental stress gradient. Moreover, patterns in seed production were opposite at the fruit and the individual scale, as a strategy of populations to maximize fitness in each set of local conditions. Finally, in the fourth chapter, we found no relationship within populations between phenotypic variability and genetic diversity. Phenotypic variation was mainly shaped by precipitation variability, suggesting adaptive variation, whereas genetic diversity was correlated with the central vs. peripheral position, probably in close relation with some random demographic processes experienced by populations in the past. Despite genetic diversity was higher in central populations, our results contradicted classical hypotheses predicting a lower demographic performance towards species’ range edges. In fact, environmental conditions seemed to have a higher influence on plant performance than the position of populations within the species’ range, which calls for the necessity of distinguishing between geographical periphery and ecological marginality in demographic studies. Overall, our study highlights the versatility of P. coronopus at different spatial scales in response to varying environmental conditions, complementing similar findings of previous research on the same taxon at smaller spatial scales. Such life-history variability seems to be a key factor for widespread plants to extend over large and heterogeneous ranges. / Las especies de amplia distribución han recibido tradicionalmente poca atención, a pesar de su importancia para la estructura y el funcionamiento de los ecosistemas. En esta tesis, se analiza la variabilidad demográfica, de historia vital y genética en una planta de amplia distribución en Europa y el norte de África (Plantago coronopus), en un total de 22 poblaciones a lo largo de gran parte del rango latitudinal de la especie (centro y periferia norte). Se pretende analizar la magnitud y las causas de esta variabilidad intraespecífica en relación con la posición de las poblaciones dentro del rango y con los principales factores medioambientales. Las poblaciones periféricas mostraron una menor diversidad genética, pero no mostraron en general un peor o más variable comportamiento demográfico en cuanto a densidad o tasa de crecimiento poblacional, contradiciendo así las hipótesis clásicas centro-periferia. Se encontró un mismo patrón de diferenciación demográfica dentro de las regiones tanto central como periférica, en relación con la variación en el régimen de precipitaciones. La tasa de reclutamiento de nuevos individuos fue el proceso del ciclo vital con mayor importancia para el funcionamiento de las poblaciones. Se encontró también una gran variación entre poblaciones en las características de las semillas (número, tamaño, mucílago y proporción de dos tipos de semilla dimórficos) en relación con el gradiente de estrés ambiental. Finalmente, la variación fenotípica dentro de las poblaciones se relacionó con la variabilidad ambiental, mientras que la diversidad genética se correlacionó con la posición central vs. periférica de las poblaciones y posiblemente con la historia demográfica de la especie. Globalmente, este estudio muestra la importancia de distinguir entre periferia geográfica y marginalidad ecológica, y sugiere que el éxito de las plantas de amplia distribución reside en una gran variabilidad demográfica y de historia vital a diferentes escalas espaciales.