Afin de préciser la distribution et l'écologie des oiseaux migrateurs paléarctiques et afrotropicaux en Afrique de l’Ouest, neuf grands types d'habitats situés au Burkina Faso ont été suivi par points d'écoute de février 2004 à novembre 2005. Contrairement aux prédictions du paradoxe de Moreau, nous démontrons que les différentes zones de savanes jouent un rôle complémentaire au cours de l’hivernage pour les migrateurs paléarctiques, et que le Sahel ne constitue pas un lieu d’étape primordial lors de la migration pré-nuptiale. En outre, nous montrons que les migrateurs n’exploitent pas plus les habitats ouverts ou dégradés que les espèces résidentes au sein d’une même guilde, et que les migrateurs paléarctiques et afrotropicaux exploitent principalement des niches écologiques différentes, suggérant que la compétition interspécifique n’est pas le principal agent structurant les communautés de résidents et de migrateurs, au moins dans cette région de l'Afrique. Au vu de l’ensemble de nos résultats, nous proposons que les migrateurs paléarctiques sont partie intégrante des communautés tropicales et qu’il existe en réalité un continuum de stratégies entre la sédentarité et la migration entre deux aires biogéographiquement distinctes au sein des espèces tropicales. / In order to unravel the distribution and ecology of palearctic and afrotropical bird migrants in western Africa, we surveyed nine major habitat types in Burkina Faso by monthly point counts from February 2004 to November 2005. In contradiction with predictions drawn from Moreau's paradox, we found that the different savanna zones hold complementary sets of species during the course of the overwintering period, and that the Sahel is not used as a critical fattening area during pre-breeding migration. In addition, we show that migrant species are not tied to more open or degraded habitats in comparison with resident species of the same feeding guilds, and that palearctic and afrotropical migrant communities use widely divergent ecological niches, which suggests that current interspecific competition is not the prominent force shaping residents-migrants avian communities Overall, our results favour the view that both palearctic and afrotropical migrant species actually belong to tropical communities, and that a continuum exists between sedentary species and migratory species that reach distinct biogeographic areas during the course of their migration.

Marine turtles exhibit strong fidelity to their nesting beaches, making the conservation of nesting beaches important for ensuring successful sea turtle populations. Conservation of these nesting beaches involves understanding how species interact with the environment and each other, and understanding how environmental change and population growth can affect the suitability of the nesting habitat. The Archie Carr National Wildlife Refuge (ACNWR) is unusual in its high density of sea turtle nesting by two species: green (Chelonia mydas) and loggerhead (Caretta caretta) turtles. The ACNWR in Melbourne Beach, Florida was established in 1991 due to the high density of loggerhead nesting, but in the time since it was established there has been a significant increase in green turtle nesting, from fewer than 50 nests in 1982 to over 15,000 in 2017. With such a high density of these two species in one relatively small area (21 kilometers of beach), the two species may compete for space. This is especially true for green turtles, which disturb large amounts of sand during their nesting process; in 2017, we observed 338 loggerhead clutches disturbed by nesting females during nesting surveys, nearly all of which were disturbed by green turtles. Using observed spatial and temporal nesting patterns for both green turtles and loggerheads on the ACNWR, I examined the effects these species may have on each other's nests now and in the future. Additionally, green turtles and loggerheads nest in different densities along the length of the ACNWR, with green turtles more concentrated in the southern portions of the Refuge. Finally, green turtle nesting begins and peaks approximately one month later on the ACNWR than loggerhead nesting. For each of these metrics, there is both considerable overlap and distinct separation between the two species. By using these metrics in a modeling approach, I estimated the probability of nest disturbance by a subsequently nesting female, ranging from 0 to 0.105, and how these probabilities are predicted to change over time with a growing green turtle population. Evaluating the carrying capacity of this beach is important in the context of habitat disturbance, including climate change and an increase in storm frequency, and informing adaptive management strategies for effective conservation.

No description available.

The requirements of true frogs on breeding sites were monitored at 19 locations in the Hradec Králové Region and the Central Bohemia Region and Vysočina Region. Specific sites were selected according to the high variability. Breeding sites are mutually different representation of true frogs, water volume, depth, water and surrounding vegetation. The data of oviposition three different species of czech frogs - moor frog (Rana arvalis), agile frog (Rana dalmatina) and common frog (Rana temporaria) - were collected in the spring months, from the end of March until the end of April, from 2012 to 2015. During this period were collected data from 927 egg clutches of these species. The data were obtained by non-invasive way - measuring of inividual clutches directly on the reproductive site. At each breeding site was also recorded the required parameters of the breeding pond and the surrounding environment (presence of true frogs, the water volume and depth of the pond, the presence and density of aquatic vegetation, surrounding vegetation, air and water temperature, pH value of water, etc.). The results presented in this work confirm that the three species of true frogs have, in some parameters, different standards to select of breeding sites. This clarification of species- specific claims is also...

Abstract The negative impact of invasive plant species on biodiversity and ecosystem functions, such as productivity and nutrient cycling has been deemed a global epidemic. To address this worldwide concern, information is needed on how the invasion process happens and how to control an existing invasion. The main aim of the research presented in this thesis was to develop a better understanding of the interacting role different mechanisms play in facilitating invasion and then link this understanding to the design of more effective control strategies. This aim is significant because traditional weed control strategies are not working. The estimated cost of controlling weeds in Australia is $1.4 billion per year in agricultural landscapes. Despite this substantial investment, invasive weed species are estimated to continue to cost the agricultural industry $2.2 billion per year in loss of yield. Current control strategies tend to focus on killing or removing an invasive plant species directly with the application of herbicides and/or mechanical removal. These strategies have proven ineffectual because the plant communities that assemble after management often remain dominated by the same invader or another. In this thesis, I use a combination of empirical and modelling techniques to investigate how disturbance regimes and competitive interactions between invasive plants and native plants can be manipulated to improve the efficacy of restoration efforts. To do this, I use the model scenario of the invasion of Eragrostis curvula (African lovegrass), an invasive grass species introduced into Australia in the early 1900s from South Africa. This species has now spread into every Australian state and territory (chapter 2). I specifically focus on two mechanisms: (1) disturbance, i.e. cattle grazing, and (2) competitive interactions. In chapter 3, I examine connections between dominance and competitive differences among African lovegrass and several functionally similar native grass species in a pasture community. To test the displacement hypothesis, I used a glasshouse competition trial to investigate interactions between African lovegrass and two non-persisting native grass species (Themeda australis and Bothriochloa decipiens) with manipulations of resources, neighbour density, and establishment order. To test the partitioning hypothesis, I compared in situ water use patterns among African lovegrass and two coexisting native grass species (Aristida calycina and Aristida personata) based on the assumption that water is the most limiting resource in this system. The key finding of this chapter is that competition can have important, but contingent, impacts on dominance. Competitive differences appear to partially contribute to abundance patterns after establishment, but may be relatively unimportant during the establishment phase where disturbance appears more critical. In chapter 4, I provide evidence that the identification of mechanisms that led to an invasion, while crucial for the development of effective preventative measures and understanding the invasion process, may not be necessary for the design of more effective control strategies. To examine the effects of different control strategies on African lovegrass and the resultant community, I established a large factorial field-trial with a split-plot design. I manipulated grazing, soil nutrient levels and the presence of the invader. The most common control strategy (removing the causal disturbance and killing the invasive grass), based implicitly on traditional equilibrium models, was not an effective option for restoring a desirable native community. Instead, this strategy led to the dominance of a secondary invader. The most effective control strategy was based on alternative stable states models and involved maintaining grazing, and increasing the palatability of the invader with fertilizers. The key finding of this chapter is that novel approaches for control, which consider the dynamics of the invader-dominated system, are needed. In chapter 5, I investigate the benefits of explicitly incorporating actions that manipulate disturbance (natural or imposed) into control efforts. To do this, I first developed a process model that described the dynamics of an invader whose establishment is preferentially favoured by disturbance. I then couched this model in a decision theory framework, a stochastic dynamic program, and applied a case-study of another invasive plant species, Mimosa pigra (a perennial legume shrub and pan-tropical weed). The key finding of this chapter is that strategies should not only focus on existing invader-dominated sites, but should also protect sites occupied by native species from disturbances that facilitate invasion. The research discussed in this thesis makes three key contributions to a better understanding of the invasion process and the design of more effective control strategies: 1) the search for one key mechanism is not sufficient because multiple mechanisms can interact or shift in importance to facilitate different stages of invasion, 2) a novel approach is needed to restore a more desirable native community because the dynamics of the invader-dominated system can differ from the historical native community, and 3) control efforts should be broadened in focus to include protection of the integrity of native communities from disturbances that facilitate invasion.

Submitted by PEDRO JULIÃO JIMENEZ null (p_j_jimenez@hotmail.com) on 2016-04-18T20:29:32Z No. of bitstreams: 1 Dissertação-de-mestrado_Pedro_Jimenez_2016 - repositório.pdf: 1264368 bytes, checksum: 9cba2282085ba20e62c6d3e74cb23964 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-04-19T17:47:28Z (GMT) No. of bitstreams: 1 jimenez_pj_me_bot.pdf: 1264368 bytes, checksum: 9cba2282085ba20e62c6d3e74cb23964 (MD5) / Made available in DSpace on 2016-04-19T17:47:28Z (GMT). No. of bitstreams: 1 jimenez_pj_me_bot.pdf: 1264368 bytes, checksum: 9cba2282085ba20e62c6d3e74cb23964 (MD5) Previous issue date: 2016-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Experimentalmente, em campo e em laboratório, usando como modelo as espécies Uca leptodactyla e U. uruguayensis, avaliamos como o estímulo direto e o estímulo visual de um competidor interespecífico pode alterar a agressividade e os comportamentos agonísticos durante as lutas intraespecíficas. Vimos que o comportamento de estender o quelípodo (ameaça), que é um comportamento pouco escalado, ocorre em menos lutas na presença do estímulo do competidor interespecífico nos experimentos em laboratório. Em U. leptodactyla, o comportamento de entrelaçar/agarrar os quelípodos, que indica combates mais escalados, esteve presente em mais lutas com o estímulo direto do interespecífico, diferindo das lutas na presença do estímulo do intraespecífico. Nos experimentos com estímulo visual, em U. uruguayensis, houve mais comportamento de entrelaçar no grupo experimental sem a presença do estímulo, diferindo do grupo experimental com estímulo intraespecífico. Nos experimentos em campo, em U. uruguayensis houve maior número do comportamento arremessar, o mais escalado analisado neste estudo, nas lutas com ausência do estímulo de competidores. Os resultados sugerem que na presença de interespecíficos ocorrem diferenças nas lutas, em que menos comportamentos de ameaça são utilizados. Parece haver identidade mal interpretada do estímulo visual dos competidores, pois não ocorrem diferenças entre os grupos com estímulo visual intra- e interespecífico. Os dados sugerem existir diferenças na ameaça oferecida pelo interespecífico para as diferentes espécies, e a avaliação que os indivíduos fazem dos adversários pode ter levado a respostas diferentes pelas espécies. / Experimentally, in field and laboratory, using as models the species Uca leptodactyla e U. uruguayensis, we evaluated how the direct and the visual stimulus of an interspecific competitor can alter the aggressivity and agonistic behaviors in intraspecific fights. The cheliped extend (threat behavior), a less scalated behavior, occurred in less fights in the presence of the interspecific competitor, in the laboratory experiments. In U. leptodactyla, the interlace/grapple behavior, that indicate more escalated combats, occurred in more fights when in the presence of the direct stimulus of the interspecific, differing of the fights in the presence of the intraspecific stimulus. In the field experiments, there was a bigger number of the flick behavior, the most escalated in this study, in the fights of U. uruguayensis when in the absence of competitor’s stimulus. The results suggest that differences occur in the fights when interspecific competitors are present, occurring less threat behaviors. It seems that occur a misidentification of the specie identity when only exposed to visual cues of the competitors, not occurring differences between the groups with the intra- and interspecific stimulus. The data suggests differences in the offered threat by the interspecific between the species, and the assessment that the individuals do about their adversaries can lead to different response by the species.

Orientador: Rodrigo Egydio Barreto / Resumo: Experimentalmente, em campo e em laboratório, usando como modelo as espécies Uca leptodactyla e U. uruguayensis, avaliamos como o estímulo direto e o estímulo visual de um competidor interespecífico pode alterar a agressividade e os comportamentos agonísticos durante as lutas intraespecíficas. Vimos que o comportamento de estender o quelípodo (ameaça), que é um comportamento pouco escalado, ocorre em menos lutas na presença do estímulo do competidor interespecífico nos experimentos em laboratório. Em U. leptodactyla, o comportamento de entrelaçar/agarrar os quelípodos, que indica combates mais escalados, esteve presente em mais lutas com o estímulo direto do interespecífico, diferindo das lutas na presença do estímulo do intraespecífico. Nos experimentos com estímulo visual, em U. uruguayensis, houve mais comportamento de entrelaçar no grupo experimental sem a presença do estímulo, diferindo do grupo experimental com estímulo intraespecífico. Nos experimentos em campo, em U. uruguayensis houve maior número do comportamento arremessar, o mais escalado analisado neste estudo, nas lutas com ausência do estímulo de competidores. Os resultados sugerem que na presença de interespecíficos ocorrem diferenças nas lutas, em que menos comportamentos de ameaça são utilizados. Parece haver identidade mal interpretada do estímulo visual dos competidores, pois não ocorrem diferenças entre os grupos com estímulo visual intra- e interespecífico. Os dados sugerem existir diferenças na ameaça o... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Experimentally, in field and laboratory, using as models the species Uca leptodactyla e U. uruguayensis, we evaluated how the direct and the visual stimulus of an interspecific competitor can alter the aggressivity and agonistic behaviors in intraspecific fights. The cheliped extend (threat behavior), a less scalated behavior, occurred in less fights in the presence of the interspecific competitor, in the laboratory experiments. In U. leptodactyla, the interlace/grapple behavior, that indicate more escalated combats, occurred in more fights when in the presence of the direct stimulus of the interspecific, differing of the fights in the presence of the intraspecific stimulus. In the field experiments, there was a bigger number of the flick behavior, the most escalated in this study, in the fights of U. uruguayensis when in the absence of competitor’s stimulus. The results suggest that differences occur in the fights when interspecific competitors are present, occurring less threat behaviors. It seems that occur a misidentification of the specie identity when only exposed to visual cues of the competitors, not occurring differences between the groups with the intra- and interspecific stimulus. The data suggests differences in the offered threat by the interspecific between the species, and the assessment that the individuals do about their adversaries can lead to different response by the species. / Mestre

Studies focusing syntopic species help to understand how they partition resources and coexist. The objective of this work was to describe the social system, habitat use and diet of the hoary fox (Pseudalopex vetulus) and the crab-eating fox (Cerdocyon thous), in an area of cattle farms in Central Brazil. It is also reported a confrontation between the two species, observed during a study on the behavioral repertory of the hoary fox. Social system and habitat use were studied by direct observation of foxes in the field and diet, through scat analysis. Crab-eating foxes were found in pairs in 34 (59%) of 58 encounters and hoary foxes were solitary in 58 (84.0%) of 69 encounters, with no seasonal variation in the group size of both species. During one encounter of a crab-eating fox couple, the male vocalized to call the female that had remained behind. Hoary foxes were sighted in grazed pasture in a higher proportion (84%) than crab-eating foxes (67%) and they were never found in forest neither in swamp. Besides, both species were rarely seen together, and the only encounter registered ended in a conflict, with the crab-eating fox driving the hoary fox out. Twenty-seven taxa were identified in the diet of the two canids, with the crab-eating fox (n = 32 scats) consumed fruits, insects (mainly Orthoptera and Coleoptera) and vertebrates (most Cricetidae and Squamata) and the hoary fox (n = 23 scats) ate primarily termites (Isoptera). Results indicate that crab-eating fox couples keep more tight bonds than hoary fox couples. The coexistence of both species may be related to the detected differences in habitat use and diet. / Estudos enfocando espécies sintópicas ajudam a entender como elas partilham os recursos e coexistem. O objetivo deste trabalho foi descrever o sistema social, o uso do habitat e a dieta da raposa-do-campo (Pseudalopex vetulus) e do cachorro-do-mato (Cerdocyon thous), em uma área de fazendas de gado no Brasil Central. Também é relatado um confronto entre as duas espécies observado durante um estudo sobre o repertório comportamental da raposa-do-campo. O sistema social e o uso de habitat foram estudados a partir da observação direta dos animais no campo e a dieta, através da análise de fezes. Os cachorros-do-mato foram encontrados em duplas em 34 (59%) de 58 encontros e as raposas-do-campo estavam solitárias em 58 (84%) de 69 encontros, não havendo variação sazonal no tamanho de grupo das duas espécies. Durante um dos encontros de uma dupla de cachorro-do-mato, o macho vocalizou para chamar a fêmea que havia ficado para trás. As raposas-do-campo foram avistadas em pastagens em uma proporção maior (84%) que os cachorros-do-mato (67%) e nunca foram encontradas em florestas ou brejos. Além disso, as duas espécies raramente foram vistas juntas, sendo que o único encontro registrado terminou em conflito, com o cachorro-do-mato expulsando a raposa-do-campo. Vinte e sete táxons foram identificados na dieta dos dois canídeos. O cachorro-do-mato (n = 32 fezes) consumiu frutos, insetos (principalmente Orthoptera e Coleoptera) e vertebrados (a maioria Cricetidae e Squamata) e a raposa-do-campo (n = 23 fezes) se alimentou principalmente de cupins (Isoptera). Os resultados indicam que casais de cachorros-do-mato mantêm laços mais estreitos que casais de raposa-do-campo. A coexistência de ambas as espécies pode estar relacionada às diferenças detectadas no uso do habitat e na dieta. / Mestre em Ecologia e Conservação de Recursos Naturais

La connaissance des facteurs qui influent sur les populations de tiques et en particulier sur leurs distributions est un préalable indispensable à l’étude des maladies qu’elles transmettent. Parmi eux, l’importance des facteurs biotiques et en particulier celle de la compétition interspécifique est peu connue et souvent négligée. L’objectif de ce travail était d’évaluer le rôle de la compétition interspécifique sur la distribution de deux espèces de tiques d’importance vétérinaire, Amblyomma variegatum et A. hebraeum. Alors que seule A. variegatum favorise la transmission de la dermatophilose, une maladie de peau débilitante pour les ruminants, les deux espèces sont vectrices de la cowdriose, maladie due à une bactérie Ehrlichia ruminantium qui représente une contrainte économique majeure pour l’élevage. L’impact de l’espèce vectrice dans l’épidémiologie de la cowdriose (différences de souches circulantes, sévérité des cas,…) est inconnu bien qu’ayant potentiellement des conséquences en termes de surveillance (risque épidémiologique à l’introduction d’animaux) et de contrôle (développement de vaccin régional adapté aux souches circulantes) de la maladie. Ces deux espèces ont une distribution contiguë en Afrique australe avec peu de chevauchement (distribution parapatrique) suggérant une préférence environnementale différentielle ou une compétition exclusive entre elles. Une revue des données de la littérature a permis de mettre en évidence un chevauchement de leur niche trophique, climatique, et temporelle, et une interférence comportementale via la production de leurs phéromones. Les deux espèces pourraient donc rentrer en compétition directement par interférence communicative ou reproductive (hybridation stérile), ou indirectement via le partage de ressources, prédateurs ou pathogènes communs. Le rôle des facteurs biotiques et abiotiques sur le maintien de la parapatrie de ces deux espèces a été analysée (i) d’une part par la comparaison de leur niche environnementale réalisée en Afrique australe, et aux deux zones de contact au Zimbabwe et Mozambique, par des méthodes d’ordination et de modèles de niche (Maxent) ; (ii) et d’autre part par l’étude de leurs distributions et de leurs interactions (distribution sur les hôtes, croisements hétérospécifiques) dans la zone de contact au Mozambique. Globalement les résultats montrent qu’en Afrique Sud-Est et au Zimbabwe les deux espèces occupent des niches environnementales distinctes, celle d’A. hebraeum incluant des zones plus chaudes et plus sèches que celle d’A. variegatum. Au contraire au Mozambique les deux niches se chevauchent considérablement. L’enquête de terrain dans cette zone montre que les deux espèces y sont moins souvent trouvées en sympatrie que les données prédites, suggérant une distribution en partie déterminée par des interactions biotiques. Dans les rares sites avec présence des deux espèces, A. variegatum et A. hebraeum partagent les mêmes sites de fixation sur les animaux et forment un pourcentage relativement élevé de couples hétérospécifiques. Ce pourcentage, bien que similaire entre les femelles A. variegatum et A. hebraeum, semble impliquer des processus de discrimination spécifique propres aux deux espèces intervenant au niveau de l’agrégation, de la fixation et du contact des individus. Nos résultats suggèrent l’existence d’une compétition exclusive entre les deux espèces, due à une compétition sexuelle probablement associée à une compétition indirecte. La frontière parapatrique semble occuper une position stable le long d’un gradient environnemental au Zimbabwe mais pas au Mozambique. Les conditions entrainant la coexistence ou l’exclusion des deux espèces avec formation d’une frontière parapatrique sont discutés à l’aide de modèles théoriques de compétition. / Studying the factors that influence tick populations and their distributions is an essential pre-requisite to understanding the dynamics of the diseases they transmit. The relative importance of biotic factors such as interspecific competition is not well known and often neglected. The objective of this study was to assess the influence of interspecific competition on the distribution of two tick species of veterinary importance, Amblyomma variegatum and A. hebraeum. Whereas only A. variegatum is known to favor dermatophilosis, a debilitating skin disease of ruminants, both species are good vectors of Ehrlichia ruminantium, the bacteria causing heartwater, a fatal disease of ruminants that presents a major constraint for livestock development in Africa. The impact of vector species in heartwater epidemiology (differences of circulating strains, severity of clinical cases…) is poorly known but may have important implications for surveillance (epidemiological risk of imported animals) and control (adapting regional vaccine programs to circulating strains) of the disease. These two ticks have abutting and marginally overlapping (i.e. parapatric) distributions in southern Africa, suggesting either differential environmental preferences or exclusive competition between the two species. A review of published data highlighted an important overlap of their trophic, climatic and seasonal niche, and existence of chemical behavior interference through pheromone production. Therefore, the two species might compete either directly by communicative or reproductive interference (sterile hybridization), or indirectly by sharing the same resources, predators or pathogens. The role of biotic and abiotic factors in determining parapatry of these species was assessed by (i) comparing their realized environmental niche in southern Africa, and at contact zones in Zimbabwe and Mozambique, using ordination techniques and environmental niche modeling (Maxent); (ii) studying their distributions and their interactions (distribution on co-infested host, heterospecific mating) at the contact zone in Mozambique. Globally, the results indicated the two species occupied distinctly different environmental niches in southern Africa and at the contact zone in Zimbabwe, with the niche of A. hebraeum including both hotter and drier areas than that of A. variegatum. However, in Mozambique their niches overlapped considerably. Field studies within this zone showed that sympatry was observed less frequently than predicted by niche models, suggesting an importance of biotic interactions. At the rare sites where both species were present, A. variegatum and A. hebraeum were observed to share the same preference sites on hosts and formed a high percentage of heterospecific pairs. Though this cross-mating rate was not significantly different between A. variegatum and A. hebraeum females, our observations suggest different mechanism of species discrimination involved for the two species acting at the aggregation, fixation and partner contact level. Our results strongly suggest exclusive competition between these species may arise from sexual competition probably interacting with other indirect forms of competition. The parapatric boundary apparently occupies a stable location along an environmental gradient at the contact zone in Zimbabwe but not in Mozambique. Conditions inducing coexistence or exclusion of both species with the formation of parapatric distributions are discussed in relation to theoretical models of competition. When sexual competition is introduced in these models, the relative frequency of two species is determined by their endogenous fitness (a function of environmental conditions), density dependent effects of competitive interactions, historical distributions and dispersal rates: survival of the first prevails when the immigration rate of a fitter invading species remains lower than an invasion threshold.

Abstract My main objectives in this thesis were to explore general patterns and mechanisms driving salmonid invasions globally and, more specifically, to examine the invasion dynamics and impacts of the North American brook trout in North European stream systems. Non-native salmonids have often spread extensively and caused many harmful impacts on their native counterparts. Among the three globally introduced salmonids, the European brown trout appeared as the 'worst' alien species (strongest impact on native fish), followed by the North American rainbow trout and brook trout. Brook trout, which is widely established in European streams, was found to be a non-aggressive species. Moreover, the growth of brown trout was unaffected by brook trout, indicating negligible interspecific interactions between the two species. Habitat niche segregation between brook trout and brown trout was evident, with brook trout occupying mainly low-velocity pool habitats, whereas brown trout resided in fast-flowing riffles. At the river-wide scale, brook trout occurred mainly in small, slightly acid headwater streams, whereas brown trout was found primarily in larger downstream river sections. Evidently, North European streams with a very low number of native fish species offer underutilized niche space for tolerant headwater specialists such as brook trout. However, the habitat niche filled by brook trout was not completely vacant, as brown trout co-occurred with brook trout in numerous small and mid-sized (3–16 m wide) streams. In these streams, brown trout reproduction was negligible presumably related to the presence of brook trout. Brook trout had also increased in density relative to brown trout during the 10-yr study period (1994 vs. 2004). Moreover, the growth rate and population densities of brook trout were high and the species had spread extensively towards the upmost headwater streams during the 10-yr study period. Thus, harmful effects on the native brown trout by brook trout are likely to occur in the core habitat of the invader, i.e. headwater streams, leaving populations of the native species unaffected elsewhere. Due to the high conservation value of the potentially impacted populations of brown trout, I strongly caution against further stocking of brook trout in European watersheds.