Population ecology is a scientific discipline primarily interested in the ecological processes that make the number of individuals in a population to change over space and time, and by focusing on populations as fundamental units, this discipline allows studying processes at multiple scales of ecological complexity, linking basic ecological science with evolutionary studies and more applied disciplines such as conservation biology. Inference about the responses of population to change are made via observational studies that focus at either the individual or population level in order to estimate key vital rates and to determine the primary drivers of system dynamics. However, a problem of observational studies is that quite often the ecological and observational processes are confounded, leading to biased estimates and wrong conclusions about a population, so more specific and robust analytical approaches need to be applied for a correct scientific study of the populations. In this thesis, I have consistently applied a methodological approach that allows the study of population processes by separating ecological and observational processes via the estimation and modelling of key demographic parameters. By means of chapters 1 to 4, I provide several examples of this methodology via the analysis of demographic data belonging to different species and levels of population complexity that also reflect different biological questions and scientific applications. Field data for this thesis was collected using either capture-recapture or detection-non detection sampling techniques and were provided via collaborations with different researchers and institutions. Chapters 1 and 2 focus on discrete mediterranean tortoise (Testudo hermanni) and brown trout (Salmo trutta) populations, respectively. These populations are closed to dispersal processes and in both chapters I focused on stage-dependent local survival rates that were estimated using capture-recapture models that take into account recapture probabilities. Given that individuals were classified according to body size, in the case of the brown trout populations, I could apply multistate capture-recapture models to estimate individual growth and maturation rates across different populations. In both chapters, survival dynamics were modelled using external covariates (temperature and/or precipitation) that explained part of the observed variation in survival. In the case of tortoises, the obtained survival-precipitation relationship was used to perform several population viability analyses under future precipitation scenarios to forecast the extinction risk of the species across their global geographic distribution. Chapters 3 and 4 focus on population networks connected by dispersal processes. Chapter 3 is strictly focused on adult dispersal and so analyses a capture-recapture dataset collected over 4 local populations of Audouin’s gull (Larus audouinii) in the Western Mediterranean. In Chapter 4 I analysed a large database on butterfly species collected at 26 sites in Catalonia over 17 years and focused on species’ extinction-colonization dynamics at a large geographical scale. In both chapters, two relatively recent analytical approaches, the multievent modelling (chapter 3) and the multiseason or dynamic occupancy modelling (chapter 4) were applied. The application of such modelling tools allowed, in the case of gulls, to control recapture heterogeneities and to study individual dispersal both in and out of the study area, by means of the addition of unobservable states in the model. In the case of butterflies, a common candidate model set was applied to 73 butterfly species, obtaining specific extinction and colonization rates corrected for species’ detectability, which allowed assessing the influence of the species’ traits on occupancy dynamics. Covariate modelling became much more complex in these chapters, but allowed the identification of different habitat and environmental variables related to dispersal, extinction and colonization processes that are of high value in the conservation and management of the species under study. / L’ecologia de poblacions és una branca multidisciplinària de l’ecologia que, al considerar les poblacions com a unitats biològiques fonamentals, permet establir nexes d’unió entre l’ecologia bàsica, els estudis evolutius i la biologia de la conservació. L’estudi de les respostes demogràfiques als canvis ambientals es realitza per mitjà del monitoratge de poblacions, però per a un coneixement detallat dels processos ecològics que determinen les dinàmiques poblacionals cal fer server eines d’anàlisi robustes que ens permetin estimar i modelitzar paràmetres poblacionals tenint en compte la detecció imperfecta dels processos ecològics. Aquest enfoc metodològic ha estat aplicat a l’anàlisi de les dades de monitoratge poblacional dut a terme en aquesta tesi, on cada capítol representa una aplicació metodològica per a respondre a qüestions biològiques específices al llarg de diferents nivells de complexitat ecològica. Els capitols 1 i 2 és centren en poblacions discretes de tortuga mediterrània i truita comuna, respectivament. En aquest capítols vaig aplicar diferents models de captura-recaptura per obtenir estimes de supervivència per a diferents estadis vitals, i, en el cas del capitol 2, estimes de creixement individual. L´ús de covariables va permetre avaluar l’efecte de la meteorologia en la supervivència, i en el cas de la tortuga, aquesta relació fóu utilitzada per a realitzar simulacions sota diferents escenaris de canvi climatic, proporcionant riscos d’extinció al llarg de tota la distribució mundial de l’espècie. Els capitols 3 i 4 es centren en l’estudi de xarxes poblacionals i en concret, en l’estudi de la dispersió i els processos d’extinció i colonització d’espècies fent servir com a models biològics la gavina corsa i la comunitat de papallones diurnes de Catalunya. En el cas de la gavina, vaig aplicar models de captura-recaptura multievent per controlar biaixos i obtenir estimes de dispersió adulta tant a dins com a fora de l’àrea d’estudi. L’aplicació de models d’ocupació dinàmica va perpetre obtindre estimes robustes de probabilitats d’extinció i clonització per a 73 espècies de papallones. En ambdòs casos, diferents variables externes varen ser examinades i es varen identificar diferents factors ambientals relacionats amb processos de dispersió i recanvi poblacional que poden ajudar al desenvolupament d’estratègies de conservació.

Tesi realitzada al Centre d’Estudis Avançats de Blanes (CEAB / CSIC) / Overall, this thesis aims at approaching macrophyte herbivory and community ecology from a behavioural landscape perspective. Our study system, the seascape mosaic of Posidonia oceanica seagrass meadows interspersed with sand patches and rocky areas with macroalgal cover, is particularly useful to test sound ecological questions. In essence, the macroherbivore community is made up of just two key species, the sea urchin Paracentrotus lividus and the fish Sarpa salpa. Both species are generalists and have been found to actively consume seagrass and macroalgae, profoundly altering habitat structure. Moreover, both animals differ in their mobility and in the predation risk they are subjected to, which poses interesting questions on how they will perceive, use, respond to and impact their surrounding seascape. S. salpa is a highly mobile species with few known extant predators, while the sea urchin P. lividus is a low mobility species with high rates of predation. The thesis is structured in five chapters that focus on different aspects of community organization and ecological interactions (chapter 4), animal movement (chapters 5 and 6), animal risk assessment and behavioural responses to predation risk (chapter 5), habitat selection and connectivity (chapter 6), influence of seascape attributes on herbivore foraging and thus on herbivores’ impacts on plants (chapter 7) and herbivores’ responses in terms of population and behaviour to disturbances (chapter 5). Chapters derive from field manipulative experiments (chapter 4), field mensurative campaigns (chapters 6, 7 and 8) or controlled experiments in the laboratory (chapter 5). In chapter 4 we observed that predation pressure on a key herbivore (sea urchin) can be modified both by the environmental context within which it finds itself and by the actions of another herbivore (S. salpa) that modifies the plant traits that create this environmental context (P. oceanica). Herbivores, particularly when acting as ecosystem engineers, may have the potential to mediate and increase predation risk, as they substantially modify habitat structure with consequences for refuge availability, among others. Indeed, this type of interactions may be stronger or softer according to prey movement patterns and their perception of risk. Sea urchins can perceive predator chemical cues and respond escaping from these stimuli altering their behaviour by switching among different movement patterns. Predation risk may be as important in determining animal movement patterns as feeding strategies, and in chapter 5 sea urchins responded with straighter paths in the presence of predator cues. We were also interested in the movement patterns of the other key herbivore of the system (chapter 6). The herbivorous fish S. salpa displayed large home ranges and connected distant habitats with their highly mobile behaviour. In spite of their mobility, they also displayed a strong selectivity for the seagrass habitat, which was preferred over the rocky and sand areas. Highly mobile species can connect distant habitats, and may perceive the landscape at a greater scale. The knowledge gained on the movement patterns of both herbivore species allowed us to assess the influence of seascape attributes on the herbivory patterns found in P. oceanica seagrass meadows. The observed spatial heterogeneity in the herbivory process may be mediated by the interaction of mobility of the two main herbivores (sea urchin and fish) with seascape configuration and predation risk. We finally proved that herbivores’ species-specific behaviour could lead to contrasting responses in the face of extreme storm events. Under catastrophic disturbances, the presence of different responses among the key herbivores of the system may be critical for the maintenance of functions. Differences in species behaviour and movement capacities explain why the most mobile species (in our case S. salpa) have the possibility to endure extreme storms, while the low-mobility species is subject to great population losses just relying on the structural complexity of the habitat to resist. Overall, we feel convinced that merging the behavioural and landscape approaches can result in new views in the ecology of functions such herbivory, in which at least two species interact among themselves framed by a given landscape configuration. / Aquesta tesi pretén aproximar-se a l’estudi de l’herbivorisme dels macròfits marins i a l’ecologia de comunitats des d’un punt de vista comportamental i de paisatge. Volem estudiar com en un sistema relativament senzill, els dos herbívors claus (el peix Sarpa salpa i la garota Paracentrotus lividus) interactuen entre ells, i com els seus aspectes comportamentals interactuen també amb la configuració del paisatge i l’hidrodinamisme. El nostre sistema d’estudi és el paisatge format per praderes de la planta marina Posidonia oceanica barrejades amb àrees de sorra i zones rocoses amb macroalgues. La tesi s’estructura en cinc capítols. El primer tracta de com la pressió de depredació sobre un herbívor clau (garotes) pot ser modificada tant pel context ambiental en què es troba com per les accions de peixos herbívors (salpes) que modifiquen els trets de la planta marina (posidònia) que crea aquest context ambiental. Aquestes interaccions seran més o menys intenses en funció de com reaccionin els individus presa davant dels depredadors. Per això vam estudiar el comportament de les garotes en funció de la presència o absència de senyals químics de depredadors. Vam observar que responen amb canvis en els seus patrons de moviment, amb trajectòries més rectilínies en presència de depredadors. També ens interessava entendre els patrons de moviment de l’altre herbívor del sistema, el peix S. salpa. Els nostres resultats mostren que aquest peix herbívor presenta grans àrees de campeig i que té la capacitat de connectar hàbitats distants gràcies a la seva gran mobilitat. Alhora, les salpes mostren una gran selectivitat per l’habitat de P. oceanica, que sembla clarament preferit sobre les àrees rocoses i de sorra. Els coneixements obtinguts sobre els moviments dels eriçons i les salpes ens van permetre estudiar la influència dels atributs de paisatge en l’herbivorisme en praderes de P. oceanica. L’heterogeneïtat espacial observada en l’herbivorisme és produïda, possiblement, per la interacció entre la mobilitat dels dos herbívors principals del sistema (garotes i salpes), la configuració del paisatge i el risc de depredació. Finalment, vam poder comprovar que les diferències de comportament observades entre els dos herbívors estudiats van implicar respostes dispars de les dues espècies davant una tempesta extrema, cosa que pot ser crítica pel manteniment de les funcions ecosistèmiques. En conjunt, estem convençuts que la unió dels punts de vista que aporten l’ecologia del comportament i l’ecologia del paisatge poden resultar en una millor i més completa comprensió de funcions ecològiques com l’herbivorisme, en les quals almenys dues espècies interaccionen incloses en un paisatge determinat.

Tesi realitzada al Centre d'Estudis Avançats de Blanes (CEAB-CSIC) / The main goal of this PhD thesis was the study of the ammonium oxidation process in high nutrient loaded urban streams. We aimed to unveil regulating factors and driving mechanisms from the organisms to the ecosystem scales using a combined biogeochemistry-microbial ecology approach. Ammonia oxidization is the first and rate-limiting step of nitrification. Nitrification is the key process linking nitrogen (N) inputs (fixation, mineralization) and losses (denitrification, anamox) in the aquatic ecosystem. Ammonia oxidizing archaea (AOA) and bacteria (AOB) drive this process through the enzyme ammonia monooxygenase. Although sharing a common function, AOB and AOA are phylogenetically distinct, suggesting different evolution and phenotypic characteristics. AOA and AOB were detected in the stream biofilms. The abundance, community composition and distribution of these microbial components were driven by environmental physical and chemical conditions, mainly ammonia (NH4) concentrations and sun irradiance. Ammonia oxidizing activity in biofilms under low NH4 availability was low and only 2 % of the inorganic NH4 was nitrified. Under these conditions AOA dominated ammonia oxidizing community and were key players of the observed ammonia oxidation (Nitrososophaera cluster). Conversely, under high NH4 load in the stream up to 100 % of the inorganic NH4 was oxidized to nitrate (NO3). Such high ammonia oxidizing activity was mostly driven by AOB (Nitrosospira and N. oligotropha clusters). Under these conditions AOB outnumbered AOA by orders of magnitude. AOA in contrast were poorly active under high NH4 concentrations and a consistent community composition shift was observed between high and low NH4 conditions. In laboratory cultures the growth of AOA and AOB was immediately inhibited by light. In particular, at lower light intensities, archaeal growth was much more photosensitive than bacterial growth and unlike AOB, AOA showed no evidence of recovery during dark phases. These findings provide evidence for niche differentiation in aquatic environments and suggested light as a main driving factor for the distribution and activity of ammonia oxidizers in the aquatic environment. Accordingly, in early stage biofilms developing on streams cobbles the percentage of ammonia oxidizers was higher in darkness (i.e., sediment facing side or dark-side biofilms) than in biofilms grown on the upper, light exposed side of the cobbles (light-side biofilm). However, this spatial segregation was missed in mature biofilms suggesting that the complex microbial structure present in light-side biofilms may protect both AOA and AOB against photoinhibition. This finding was further confirmed by a significant relationship found between light-side biofilm biomass and the abundance of ammonia oxidizers in situ. In contrast, for dark-side biofilms the relationship was missed. Therefore, irradiance was not an inhibitory factor for AOA and AOB in mature light-side biofilms probably due to an “umbrella effect”. The umbrella effect and the fact that AOA and AOB were highly abundant in the sediment (light avoiding strategy) are probably the reasons why nitrification at the ecosystem scale was independent from both light intensity and dial light cycling. Altogether these results highly contributed to improve the current knowledge on nitrification in urban streams and provided insights on niche differentiation between AOA and AOB. / El objetivo de esta tesis ha sido el estudio de los mecanismos y factores reguladores del proceso microbiano de oxidación del amonio (NH4) en ríos urbanos afectados por vertidos de depuradoras. Arqueas (AOA) y bacterias (AOB) oxidadoras de amonio (OA) fueron detectadas en comunidades microbianas (biofilms) desarrolladas sobre los cantos rodados del río. Su abundancia, composición, distribución y actividad fueron examinadas, con técnicas de ecología microbiana molecular y de biogeoquímica fluvial, en estudios realizados con cultivos, microcosmos e in situ. Tanto la concentración natural de amonio (NH4) como la radiación solar fueron factores clave en la regulación de dichos parámetros de los AO. En condiciones ambientales de baja concentración de NH4, las AOA (cluster Nitrososophaera) dominaron la comunidad de OA, mostrando una baja actividad nitifricante. Bajo altas concentraciones de NH4, las AOB eran dominantes (clusters Nitrosospira y N. oligotropha) y mostraban una alta actividad. En cultivos monoespecíficos, el crecimiento de AOA y AOB fue inmediatamente inhibido por luz. Las AOA mostraron una mayor fotosensibilidad y una menor capacidad de recuperación que las AOB. Estos hallazgos sugerían que la luz podría ser un factor determinante en la distribución y actividad de OA en ecosistemas naturales. En concordancia, en biofilms naturales incipientes se observó mayor preferencia de las OA para colonizar las superficies orientadas hacia el sedimento que para colonizar superficies orientadas hacia la luz solar. Esta segregación espacial no se observó en biofilms maduros. Además, se observó una relación significativa entre biomasa total y abundancia de OA para los biofilms del lado luminoso pero no para los del lado oscuro. Este hecho sugiere la existencia de un efecto fotoprotector in situ (efecto “sombra”). Este efecto podría explicar porque la nitrificación medida a nivel de tramo fluvial fue independiente de la intensidad de la luz y del ciclo solar diario. Las poblaciones de OA fueron también abundantes en el sedimento. Sin embargo, la partición de la contribución de sedimento y biofilms a la nitrificación de un tramo fluvial desveló un papel proporcional preponderante de las poblaciones de OA que se desarrollan en biofilms protegidos de la luz.

Water availability is one of the biggest constraints limiting the plant growth and species distribution around the world. This is the case in the Mediterranean region where, moreover, the frequency and amount of rainfall will decrease due to global warming. This will provoke longer periods of drought and a general decrease of water availability. In this context, one of the most vulnerable crops is grapevine. This crop has been traditionally rain-feed, although in recent years it’s becoming an irrigated crop. This increases the demand to regulate the water use by more precise irrigation techniques based on the plant water status. A good physiological indicator that allows knowing the plant water status is stomatal conductance. Although it is widely known the importance of the stoma, there is not an accurate model to predict their behavior as many physiological and environmental parameters co-regulate it. The aims of this thesis are to: a) study the physiological mechanisms regulating stomatal conductance, b) apply a process-based model to predict the behavior of stomatal conductance c) use this model as tool to better understand the physiological stomatal regulation along the canopy. Results show that stoma has a strong regulation by hydraulic conductance being a key physiological parameter regulating water use. In addition, abscisic acid and osmotic adjustment are also playing an important role in their regulation. On the other hand, the mechanistic model of stomatal conductance has been validated predicting with a good accuracy the variations throughout the day and season in well water and water stress conditions. At time, because this model is based on physiological parameters permits to infer about the relevance of those physiological parameters under water stress, predicting that hydraulic conductance has a main role on the regulation of stomatal conductance in different parts of the canopy.

Mosquitofish is a small, voracious, highly fecund freshwater fish species originated from northeaster America, that was introduced worldwide to control mosquito populations. In this thesis we have studied the genetics of the invasion of Mediterranean streams by the mosquitofish (Gambusia holbrooki) to discover some of the aspects that drive their successfully invasive life history. Comparison of introduced populations with the American sources of invasion indicated that there was no loss of genetic diversity due to the invasion process. Local genetic diversity levels and overall population structure were maintained among generations in introduced populations. We observed adaptive response to pollutants in the Flix reservoir, Ebro River, but that human perturbations do not prevent mosquitofish dispersal along rivers. Finally, unregulated human-assisted translocations probably increase the opportunities for colonization of new environments, and therefore need to be controlled. / La gambúsia és un peix molt voraç i fecund originari de les masses d’aigua dolça del nord-est d’Amèrica, que va a ser introduïda en tot el món pel control biològic de les poblacions de mosquit. En aquesta tesis se analitzen els processos genètics relacionats amb l’èxit invasor de la gambúsia (Gambusia holbrooki) en les conques mediterrànies. Les poblacions de gambusia introduïdes catalanes mantenen els nivells de diversitat genètica presents a les poblacions Americànes que van ser les fonts dels invasors de Europa. En aquestas poblacions introduïdes, els nivells locals i patrons hidrogràfics de diversitat genètica es mantenen entre generacions. Hi a una resposta selectiva als contaminants en les poblacions de gamusia a l’embassament de Flix, riu Ebro, però aquestes pertorbacions humanes no limiten la dispersió de la gambúsia. Finalment, les translocacions d’exemplars per l’home augmenten les oportunitats de colonitzar nous ambients i per això han de ser controlats.

El conocimiento de la estructura y dinámica de la población de una especie dada se fundamenta principalmente en el conocimiento de la fracción adulta. Hasta la fecha dicho conocimiento era mínimo para Alytes muletensis, reduciéndose a aspectos etológicos como la reproducción, y en muchos casos la información obtenida provenía de poblaciones cautivas. El presente conjunto de trabajos asienta las bases para el conocimiento de la fracción adulta, como es la identificación de los miembros de la población a partir de técnicas de fotoidentificación, así como la determinación del sexo a partir de la construcción de funciones discriminantes de clasificación sexual a partir de un estudio morfológico. Gracias a la obtención de esta metodología se ha podido continuar en el estudio de la estructura y dinámica poblacional. Así, se han comparado las longitudes y condiciones corporales procedentes de individuos de poblaciones naturales y artificiales, hecho que ha permitido conocer mejor la idoneidad del hábitat. Los individuos procedentes de poblaciones artificiales presentan una longitud y condición corporal mayor que los de poblaciones naturales, dando lugar a pensar que, desde el punto de vista del individuo, los hábitats óptimos para la especie son aquellos más similares a los artificiales. Además, se han podido establecer parámetros propios de poblaciones silvestres como es el caso del tamaño de puesta, la edad media, la esperanza de vida o la tasa de crecimiento, tanto para machos como para hembras. Estos datos han sido de vital transcendencia ya que han permitido elaborar el primer ciclo de vida sencillo con el que se han podido calcular las primeras tasas de supervivencia de cada sexo para una población silvestre. Este hecho supone un antes y un después en el conocimiento de la dinámica de la población que permitirá en un futuro mejorar este ciclo de vida en función de diferentes situaciones y tipos de poblaciones. El conjunto de trabajos realizados se complementa con la detección de los primeros casos de malformaciones en individuos adultos. También se presta especial atención a la interacción entre Natrix maura y la fracción adulta de la población, hecho que ha permitido conocer el impacto de la llegada de ejemplares de culebra viperina sobre la actividad reproductora.

Comparative studies between different enzyme labelled fluorescence (ELF) protocols and fluorescence quantification methods were performed to improve the quantification of single-cell phosphatase activity (PA) measurements in plankton. Unfixed and liquid ELF incubations were devised, and intracellular labelling was found to be unavoidable independently of the protocol. This observation arose the question whether our measurements of phosphatase and/or other extracellular enzyme activities based on ELF and other bulk substrates has been biased by their interaction with intracellular located enzymes. The comparison of fluorescence intensity quantifications in 2D and 3D widefield and restoration microscopy showed basically a linear relationship between methods across a wide range of fluorescence intensities. Measurements of fluorescence intensity based on 2D images were significantly biased by out-of-focus light, and to a lesser extent by object size, whereas deconvolved 3D microscopy resolved this problems. We, therefore, devised restorative deconvolution 3D microscopy for most applications and we discussed how 2D image-based quantifications should be interpreted. A direct trade-off relationship between PA and bacterivory was found in oligotrophic high mountain lakes phytoplankton, both at bulk and species level, thanks to the quantification of single-cell PA. In general, PA and bacterivory were widely used by the phytoplankton of high mountain lakes, increased along a gradient of nutrient demand, and the selection of one or another depended on the resources availability, which was determined by the lake type: Phosphatase activity was preferred in acidic lakes, whereas bacterivory was favoured in deep stratified lakes, with shallow lakes in an intermediate position. Communities with relatively high levels of investment in P scavenging activities mobilized up to 3.6 or 26.1 times more P by PA than by bacterivory. No allometric relationship was found between surface-to-volume ratio (S/V) and the selection of PA or bacterivory, but we detected a phytoplankton cell S/V threshold (1.24 μm-1) above which rates and percentage of cells active in PA and bacterivory clearly decreased indicating lower demand on nutrient scavenging activities in small cells (i.e. approximately in cells below 5 μm of diameter). Finally, a quantitative study of PA in Cyclotella spp. from high mountain lakes described these diatoms as the main phosphatase strategist in most of the phytoplankton communities where it was present. The adaptive advantage that this functional trait confers in P limited environments could explain the ~150-years-old expansion of Cyclotella in nutrient-poor, non-acidified, and non-shallow lakes from the Northern Hemisphere, as a response to a combination of climate warming and P limiting conditions partially enhanced by atmospheric nitrogen deposition. / Aquesta tesi es consta d’una part metodològica i una d’ecològica. Vàrem comparar diferents protocols d’enzyme labelled fluorescence (ELF) per a analitzar activitat fosfatasa (PA) a nivell unicel•lular en organismes del plàncton. Es va concloure que els protocols que incubaven sense fixar i en líquid proporcionaven millors resultats. Malauradament cap protocol no va aconseguir eliminar completament la senyal intracel•lular, la qual cosa fa pensar que tant amb ELF com amb altres substractes pel conjunt de la fosfatasa (i possiblement d’altres activitats enzimàtiques extracel•lulars) podrien haver estat contaminades per part d’enzims intracel•lulars. També vàrem concloure que la quantificació de la fluorescència generada pel substracte ELF en reaccionar amb les fosfatases es pot quantificar de manera més fidedigna emprant microscòpia deconvolutiva de restauració, amb imatges 3D, que no pas amb imatges 2D. N’assenyalem les aplicacions on és altament recomanable i debatem com interpretar les dades de 2D. D’altra banda es va estudiar la relació entre dos trets funcionals, la PA i la bacterivoria, en el fitoplàncton d’estanys oligotròfics del Pirineu. Es va observar una relació de compromís (trade-off) entre les dues activitats tant a nivell del conjunt de l’estany com a nivell específic. Les comunitats amb nivells alts d’esforç en activitats per a l’obtenció de P mobilitzaven fins a 3,6 o 26,1 vegades més P amb la PA que amb la bacterivoria. Cal destacar que es va detectar un llindar de relació superfície volum de 1.24 μm-1 per sobre del qual les taxes i percentatges de cèl•lules actives en PA i bacterivoria disminuïa. Finalment, es va quantificar la PA en Cyclotella spp., demostrant que es troba entre els estrategues més forts de la fosfatasa en els estanys estudiats. Per això proposem que l’avantatge competitiu que li confereix aquest tret funcional podria contribuir a explicar l’expansió del gènere Cyclotella durant els darrers c. 150 anys en estanys oligotròfics, no acidificats i suficientment profunds de l’hemisferi nord, com a resposta a la combinació de l’escalfament global i a condicions limitants en P, potenciades pel dipòsit atmosfèric de N.

Tesi realitzada al Centre d'Estudis Avançats de Blanes (CEAB-CSIC) / The main goal of this thesis is to investigate how (15)N natural abundances can help understanding the role of different primary uptake compartments (i.e., biofilm, filamentous algae, bryophytes, macrophytes; PUCs) on stream nutrient retention. The experimental design of this thesis involved the examination of patterns of variability in the (15)N signatures of Dissolved Inorganic Nitrogen (DIN) and PUCs at three different spatial scales: the watershed/global scale, the reach scale, and the habitat scale; as well as the (15)N transfer between them. At each level of organization, a common goal of examining how intrinsic (i.e., among PUCs) and extrinsic (i.e., environmental) factors influence (15)N signatures of DIN and PUCs was addressed, but quite different tools and experimental approaches were used depending on each scale. At the global scale, results showed that land use in the catchment is a key driver of the variability in (15)N signatures of both DIN and PUCs. In particular, (15)N signatures of DIN and PUC are higher in streams draining catchments with agriculture and urban activities than in those draining forested catchments; whereas within each stream, major among-compartments differences in (15)N signatures are between photoautotrophic and detrital-based compartments. At the reach scale, results for the different functional groups of macrophytes in streams indicate that direct assimilation of stream water DIN is occurring by submersed and amphibious species; while species of macrophytes located at the stream-riparian edge most likely rely on DIN sources other than those provided by stream water DIN. Moreover, in streams influenced by inputs from wastewater treatment plants (WWTP), DIN uptake by submersed and amphibious macrophytes seems to be mainly in the form of N03• On the other hand, results for the (15)N transfer between photoautotrophic PUCs and stream water DIN showed that variation in DIN uptake of photoautotrophic PUCs is principally driven by nutrient concentration and light incidence, rather than by the particular characteristics of each PUc. On the contrary, variation in autotrophic N turnover is more remarkable among photoautotrophic PUCs than among study reaches, suggesting an intrinsic control by the particular characteristics of each PUC on N turnover, and being relatively independent of environmental influences. Finally, results from tracer (15)N additions at the habitat and microhabitat scales revealed that spatial heterogeneity of microbial N uptake at the microhabitat scale is characterized by a mosaic of patches dominated by microhabitats of low N, with hot spots of highly active N uptake accounting for the 20% of the reach coverage. Particularly, spatial variation of epilithon N uptake at microhabitat scale is principally driven by flow velocity, while spatial variation of N uptake by detrital compartments is controlled bya combination of biophysical factors, indicating the relevance of organic matter characteristics on their role of stream water N uptake. Overall, these results indicate that the extent to which spatial variation in microbial N uptake at fine scales is integrated at the whole-reach scale is potentially affected by factors operating at the ecosystem level, such as the degree of canopy cover, which determines the relative abundance of each PUc. Results from this present thesis highlights that changes in the major land uses within the catchment, changes in the degree of riparian vegetation and/or in the DIN loads of stream ecosystems caused by WWTP inputs, or losses of spatial heterogeneity in the stream channel can have a significant incidence on the way that PUCs contribute to N cycling at the reach scale, which ultimately dictates the N dynamics of stream ecosystems.

Humans can induce contemporary evolution through harvesting wild animals. This thesis provides evidence of this process for recreational fishing at surprisingly small geographical scales. Marine fish populations are characterized by high variability in heritable individual life‐history traits which are exposed to biased fishing mortality. The life histories strategies of actual populations, which collectively reduce adult body size, mirror such biased mortality in populations exposed to limited gene flow. Because the relationship between life history and behaviour, it is very likely that fishing also induces adaptive responses in behavioural traits. Due the potential negative effects of fishing selection the productivity and quality of the fishery, this thesis recommend considering the evolutionary impacts of fishing in the management plans of species exploited by the recreational fishing / El humans poden produir evolució contemporània a través de la recol∙lecció de animals salvatges. Aquesta tesis proporciona evidencies d’aquest procés per la pesca recreativa a una sorprenent escala espacial petita. Les poblacions marines de peixos tenen una alta variabilitat individual en caràcters heretables de la història exposada a una mortalitat selectiva per pesca. Les estratègies vitals de les poblacions actuals de peixos costaners, les quals conjuntament produeixin una reducció en la mida del individu, són el reflexa d’aquesta pesca selectiva en poblacions amb baixa connectivitat. Degut a la correlació entre història vital i comportament, la pesca pot induir també respostes adaptatives en cert caràcters comportamentals. Considerant els efectes negatius de la selecció per pesca en la productivitat i la qualitat de les pesqueries, aquesta tesis recomana considerar els possibles efectes evolutius produïts per la pesca en les estratègies de gestió d’espècies explotades per la pesca recreativa. / El hombre puede producir evolución contemporánea por la recolección de animales salvajes. La presente tesis proporciona evidencias de este proceso por la pesca recreativa en una sorprendente escala espacial pequeña. Las poblaciones de peces marinos presentan una alta variabilidad en caracteres heredables de la historia vital expuesta a mortalidad selectiva por pesca. Las estrategias vitales de las poblaciones actuales de los peces costeros, las cuales conjuntamente producen una reducción en el tamaño del individuo, son el reflejo de esta mortalidad selectiva en poblaciones con baja conectividad. Debido a la relación entre historia vital y comportamiento, la pesca puede también inducir cambios adaptativos en ciertos rasgos de comportamiento. Considerando los efectos negativos de la selección por pesca en al productividad y calidad de la pesquería, esta tesis recomienda considerara los posibles efectos evolutivos inducidos por la pesca en la estrategias de gestión de especies explotadas por la pesca recreativa.

El incremento de disponibilidad de nutrientes produce cambios en la estructura y funcionamiento de los ecosistemas litorales. La eutrofización en los ecosistemas litorales mediterráneos favorece el predominio de algas epifitas de crecimiento rápido que compiten por la luz y los nutrientes con Posidonia oceanica. La herbivoría sobre los epifitos suministra la mayor parte del carbono que asimilan los consumidores primarios y secundarios asociados a la pradera. Esta tesis evalúa la importancia del consumo ejercido por la epifauna asociada a las praderas de P. oceanica en revertir los efectos de la eutrofización sobre la biomasa de algas epifitas. Los resultados muestran un incremento de las tasas de consumo en respuesta a una mayor disponibilidad de biomasa epifita si bien el consumo no es capaz de revertir los efectos del aumento de nutrientes sobre la biomasa epifita. La comunidad íctica tiene un papel marginal en la regulación de la biomasa epifita en la Bahía de Palma.