Percorrer por autor "Padilha, Janeide"
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- Evaluating brown trout as a potential biological control agent of signal crayfishPublication . Matos, Matilde; Teixeira, Amilcar; Nogueira, António B.; Padilha, Janeide; Sousa, RonaldoThis study evaluates the potential of brown trout (Salmo trutta) as a biological control of a recently established signal crayfish (Pacifastacus leniusculus) population in a protected area (Baceiro River, Montesinho Natural Park, Portugal). Five sampling sites were monitored throughout 2023. Results indicated that brown trout were able to predate on signal crayfish but did so infrequently as only 12.24% of the sampled fish showed signs of signal crayfish in their stomachs. The number of signal crayfish in the stomach contents of brown trout was also low (only 2.13% of all prey items), but accounted for 17.70% of the total biomass of all retrieved prey items. Predation was higher in the warmer months and was size-dependent, with larger fish more able to predate on this non-native crayfish species. These findings highlight that, although brown trout can prey on signal crayfish, their effectiveness as a biological control agent is limited due to their lower abundance and predation rates. However, this situation may change in the future since brown trout may increasingly consume signal crayfish as they become more familiar with this novel prey. Therefore, it is important to conserve key native populations, and even reinforce their abundance, to allow communities to develop effective resistance to non-native species. In the meantime, a multifaceted management approach that incorporates additional control strategies, such as mechanical removal, is recommended to reduce the abundance and biomass of signal crayfish, potentially mitigating their impact and helping to maintain ecosystem balance in this protected area.
- Impact of the Highly Invasive Signal Crayfish (Pacifastacus leniusculus) on Freshwater Macroinvertebrate CommunitiesPublication . Nogueira, António Barbosa; Oliveira, Bruno; Padilha, Janeide; Varandas, Simone; Teixeira, Amilcar; Sousa, RonaldoInvasive non-native species threaten freshwater ecosystems, disrupting the functioning and structure of the food chain and potentially leading to biodiversity loss. As omnivores, crayfish can modify their environment, directly affecting organisms such as macroinvertebrates. Macroinvertebrates, intermediate consumers in food chains, are influenced by both top-down and bottom-up forces, playing fundamental functional roles within freshwater ecosystems. The main aim of this study was to assess the effects of the signal crayfish Pacisfatacus leniusculus on the freshwater macroinvertebrate community in a mountainous area with very low human disturbance, while controlling for other measured environmental factors (e.g., T degrees C, pH, TDS). To this end, 34 sites (18 invaded and 16 non-invaded) in the Raba & ccedil;al and Tuela River basins (Portugal) were sampled. Comparisons were made between basins and invaded and uninvaded sites regarding abundance, biomass, richness and indices of macroinvertebrate community diversity and functionality. A total of 38,529 organisms from 133 freshwater macroinvertebrate taxa were identified. Our results showed a decline in the biomass, richness and diversity of macroinvertebrates with increasing crayfish abundance. Few differences in functional diversity were found, probably due to functional redundancy; however, crayfish did affect certain functional groups: drillers and periphyton-associated macroinvertebrates exhibited a negative correlation with crayfish abundance, whereas scrapers and gravel-associated macroinvertebrates demonstrated a positive response. In addition to the abundance of signal crayfish, temperature, total dissolved solids and pH showed some influence on the macroinvertebrate community. Overall, these findings are fundamental for better understanding, predicting and managing crayfish impacts in low disturbance areas of upper catchments. It is important to continue monitoring not only non-native crayfish populations but also macroinvertebrate (and other) communities, as our findings clearly demonstrate the sensitivity of these organisms to crayfish presence. Future research should investigate the main mechanisms of this change in the macroinvertebrate community.
- Intrapopulation differences in biological traits and impacts in a highly invasive freshwater speciesPublication . Alves, Henrique; Gonçalves, Diana; Nogueira, António Barbosa; Teixeira, Amilcar; Padilha, Janeide; Sousa, RonaldoIndividual variation assessments are essential to better understand population and community dynamics, as well ecosystem functioning. Although researchers have long recognized this aspect, only recently has evidence accumulated about the ecological importance of variation within species. The incorporation of individual variation provides an even more complete description of the effects a species may have on ecosystems and this detailed ecological knowledge can be especially important in the context of biological invasions. In this study, we used an invasion gradient of the signal crayfish Pacifastacus leniusculus in the Rabaçal River (NE Portugal) to assess possible intrapopulation differences in key biological traits and evaluate possible changes in ecological impacts. For this, we collected individuals from the core and front of an invasion gradient to characterize several traits such as abundance, size, sex-ratio, body condition, behaviour (i.e. boldness), and trophic niche. In addition, we performed two laboratory experiments to assess possible differences regarding the consumption of prey (gastropods), leaf mass loss, and nutrients release. Signal crayfish from the front of the invasion gradient have lower abundance, are larger, predominantly male, have better body condition in both sexes, exhibit increased boldness, and have higher δ 15 N and lower δ 13 C values. In addition, in experimental conditions, signal crayfish from the front of the invasion gradient consumed more gastropods and leaves and increased the concentration of nitrates and phosphates in the water. Overall, the signal crayfish has different biological traits and distinct ecological impacts along the invasion gradient in the studied river. Our study demonstrates the relevance of assessing biological traits and impacts of invasive species at the intrapopulation level.
- Trophic response of brown trout to signal crayfish invasion in a protected mountain riverPublication . Matos, Matilde; Teixeira, Amilcar; Nogueira, António B.; Padilha, Janeide; Sousa, RonaldoWe investigated the dietary response of brown trout (Salmo trutta) to the invasion of the signal crayfish (Pacifastacus leniusculus) in the Baceiro River (Montesinho Natural Park, Portugal). We analyzed 1012 stomach contents across six sites (five invaded and one non-invaded) over the year of 2023. A total of 49 distinct dietary taxa were identified. Results reveal strong spatial and temporal variation in trout diets. While aquatic invertebrates (e.g., Baetidae, Heptageniidae, Simuliidae, oligochaetes, and signal crayfish) dominated in the spring and early summer, a shift toward terrestrial insects was observed during summer. Generalized Linear Models indicated that signal crayfish biomass significantly influenced prey richness, biomass, and diversity, while multivariate analyses confirmed distinct prey assemblages across space and time. Our study also showed that signal crayfish were consumed occasionally (2.09 % of all prey items) but accounted for 17.68 % of total prey biomass. This situation suggests limited, but non-negligible, trophic incorporation of the invasive crayfish on the brown trout diet, with possible implications for brown trout condition and food web structure. This study highlights the dynamic nature of trophic interactions following biological invasions and underscores the need for integrated management strategies to mitigate the impacts of P. leniusculus in protected freshwater ecosystems.