Amphibians are among the groups of vertebrates most vulnerable to physiological changes induced by climate change. Their permeable skin, biphasic  life cycle and eggs with no shell render them extremely sensitive to small temperature and humidity changes. Their reproductive success, immune function and degree of sensitivity to chemical contaminants have been shown to be directly vulnerable to global warming. One of the most pronounced negative effects on amphibian physiology is caused by changes in the length of the winter hibernation period, a clear example of which is the increased mortality and reduced reproductive capacity of some populations of common toad (Bufo bufo): increasingly mild winters shorten their hibernation period, leading to a general worsening of the physical state of many individuals. In addition, increasingly milder temperatures prevent these amphibians from entering complete hibernation throughout the winter period, meaning they continue to consume their reserves and experience reduced body mass as a result. Loss of body mass has a direct impact on survival capability. Extreme climate events such as droughts and heat waves are also generating negative effects in some amphibian populations. There has been confirmed  considerable year-on-year decreases in populations of the Pyrenean newt (Calotriton asper) in nine gullies in the Ordesa y Monte Perdido National Park which are directly related to those years with a greater incidence of extreme climatic events (mainly floods and droughts).

Lastly, invertebrate physiology and behaviour can also be affected by changes in climate conditions. This is the case for the pine processionary (Thaumetopoea pityocampa), the populations of which have increased their reproductive success and distribution over recent years in some areas of the Pyrenees as a result of an increase in minimum temperatures and a reduction in the number of days with rainfall.

Migratory species and those (both terrestrial and aquatic) whose body temperature depends on the temperature of the environment are particularly vulnerable to these changes. Phenological changes are not only good climate change indicators but are also hugely significant from an ecological perspective. They can affect the ability of different species to compete and therefore the structure of communities, in effect changing how the ecosystem functions as a whole.

In the case of migratory birds, the greater climatic variability of recent years is changing the migratory patterns of some species in the Pyrenees. The main changes recorded include earlier arrival on the European continent in spring (observed in more than 100 species), leaving later in autumn, and general changes in migratory patterns, the latter being particularly pronounced in birds which migrate short distances. Earlier arrival to Europe has been linked to the increase in winter temperatures in Sub-Saharan Africa (where the majority of these species winter), and the later exit in autumn seems to be related to the high temperatures recorded in the migratory destinations. It has been calculated an average advance of the arrival date of around 0.16 days per year since 1959, up to a maximum of 0.27 days per year for some species.

Phenological changes also affect invertebrates. Among insects, studies of Lepidoptera and the main pollinators have showed these to be particularly sensitive to temperature changes. Earlier first-sighting dates have been recorded for the majority of Lepidoptera species studied, seemingly related to the increase in average temperatures.

It is highly likely that the current trend in phenological changes in many animal species will remain the same or even intensify in the future as temperatures and climatic variability increase because of global warming. In addition to modifying the phenological calendars of some species, the combined effect could seriously alter some inter-species interactions, with consequences at all levels of the food chain and impacts on the dynamics of many species and high mountain ecosystems. 

In general terms, it is estimated that the range of European species has been displaced by an average of roughly 17 km towards higher latitudes and/or 11 m towards higher altitudes, per decade. A critical factor affecting mountain fauna is that ascending displacement is often limited by other human-derived factors such as habitat fragmentation or land use changes. These factors can alter connectivity between geographical areas and hinder migrations towards higher altitudes, therefore affecting the capacity of different species to adapt to the new climate conditions. Furthermore, displacements in high mountain areas entail loss of habitat, since species range inevitably reduces with increasing altitude. As a result, some species run the risk of being gradually isolated in the small remaining areas of suitable habitat, thus increasing their vulnerability and even their risk of extinction owing to food scarcity and decreasing genetic variability  in their populations.

For the majority of high mountain species, the lower limit of their range is restricted by unsuitable climate conditions, while the upper limit is determined by the availability of certain vegetation, plant species or habitat. Hence, changes in the distribution of Pyrenean species will also depend on the capacity of vegetation to shift their ranges over time: if plant communities are displaced more slowly than the rate at which climate conditions change, the potential new distribution areas of many animals could be considerably smaller than their original ranges.

Moving on to mammals, endemic high mountain species with low dispersal capability seem to be more sensitive to the effects of climate change on their range. One example is the Pyrenean desman (Galemys pyrenaicus).  The average summer temperatures and changes in water balance seem to be the main factors which determine the presence and potential distribution of G. pyrenaicus, and both are predicted to vary significantly throughout this century as a result of global warming. If the projections in this model are validated, the effects of climate change could act in synergy with habitat loss to endanger the future of the species.

Some bird species could also see their ranges reduced in the Pyrenees. Although their ability to fly considerably increases their dispersal capability, the reduced range of the plant communities on which many species depend could be decisive for some, such as the Pyrenean rock ptarmigan (Lagopus muta pyrenaica).

Las respuestas fenológicas y los cambios en la distribución de las especies tienen potenciales repercusiones negativas en las especies de niveles tróficos superiores y en general en aquellas especies que interactúan entre sí a través de sinergias de distinta naturaleza (relaciones interespecíficas). Algunos ejemplos son los casos de los sistemas herbívoro-planta, o depredador-presa, ya que los cambios en la presencia y/o abundancia que afectan a una determinada especie inciden también en las demás especies relacionadas, a través de desfases o desajustes entre los calendarios fenológicos. Estos desfases pueden alterar la capacidad de algunas especies para ejercer funciones clave en el ecosistema, y como consecuencia también el funcionamiento del ecosistema.

Phenological responses and changes to species distribution entail potential negative repercussions on species at higher trophic levels  and generally on species which interact with one another via different types of synergies (interspecific relationships ). Some examples are herbivore/plant systems or predator/prey relationships. Changes in presence and/or abundance which affect a certain species also impact other related species by causing the temporal misalignment of their phenological calendars. Said misalignment can affect the capacity of some species to carry out key functions in the ecosystem and how the ecosystem functions.

Altitudinal displacement of native species’ ranges may favour the expansion and establishment of some non-native species, since these gain access to new climatically suitable niches and low levels of competition for resources owing to the displacement of the species which originally occupied the area

Similarly, it is likely that some protected areas which are currently interconnected by natural or artificial corridors will end up cut off to certain species which cannot tolerate the new climate conditions in these corridors. This phenomenon could become particularly evident in protected areas housing endemic species with lower dispersal capability and a highly specialised ecology.

• Protect the most representative areas of the Pyrenees in terms of conservation biology. This applies especially to unique habitats which are particularly sensitive to climatic variability or which are in a delicate state of balance with environmental conditions;
• Reduce knowledge gaps and uncertainties around the potential introduction and spread of plagues, disease vectors and non-native invasive species and develop strategies for combating these;
• Incentivise the creation of new networks for observing the effects of climate change on biodiversity, and promote the development and long term maintenance of existing high mountain observation networks;
• Promote the integration of climate change adaptation considerations in current plans, programmes and other tools for planning and protection of biodiversity in the Pyrenees;
• Limit habitat fragmentation, and as far as possible ensure gradual ecological connectivity between protected areas in the Pyrenees;
• Drive research which looks jointly at climate factors and anthropic risks; 
• Promote collaboration and information exchange between the competent bodies for biodiversity protection and management in the different regions. Identify and involve representatives from land use planning, from the veterinary, livestock, agriculture and forestry sectors, and from the competent bodies for the environment and protected areas management;
• Identify the areas and species which are most vulnerable to climate change and to global change in general so as to define priority conservation areas and restoration opportunities
• Strengthen and redirect current plans for monitoring and control of vulnerable Pyrenean species and those for prevention, control and management of invasive non-native species and plagues based on potential climate-induced impacts;
• Update species’ red lists based on their current and potential vulnerability to climate change;
• Encourage the creation of cross-border databases, such as the Pyrenean atlases of plant and animal species;
• Promote the creation of mechanisms, methodologies and participative forums for coordinating inter-sectoral and cross-border adaptation measures to ensure the protection of Pyrenean species and habitats which are particularly vulnerable to climate change;
• Raise public awareness of the importance of, and risks associated with, the problem of invasive non-native species and their interactions with climate change, and inform interested groups about good practices for preventing new introductions;
• Encourage the dissemination of citizen science initiatives in the Pyrenees i.e. effective collaborations between the public and researchers to enrich databases for species phenological monitoring, observations of sensitive ecosystems, gathering sample data and archives;
• Ensure proper dissemination of approved adaptation actions, the progress of these and their results to all interested parties and society in general.
• Incentivise the design of nature-based adaptation solutions to improve the possibility of migration and of distribution changes in the protected areas of the Pyrenees by means of green corridors between them (improve ecological connectivity);
• Improve the characterisation of micro climatic changes in different populations, refuges and variable climatic gradients to a reasonable scale;