Maria J. Cruz

Colonization of freshwater habitats by an introduced crayfish, Procambarus clarkii, in Southwest Iberian Peninsula

The introduction of some crustacean species has produced alterations of freshwater environments and declines of native species worldwide. The red swamp crayfish, Procambarus clarkii Girard, was introduced in the Southwest Iberian Peninsula in the 1970’s, producing severe impacts on rice agriculture and on native biota such as macrophytes, gastropods, native crayfish and amphibians. We studied the distribution of P. clarkii in two areas of SW Iberian Peninsula: the Sado River basin (SW Portugal), an area colonized by this species around 1990, and the Parque Natural del Entorno de Doñana (SW Spain), colonized soon after its introduction in the Iberian Peninsula, in the 1970’s. Our main goal was to determine which factors limit crayfish distribution, which could help to identify the most effective management practices to contain its spread. Procambarus clarkii was found in most types of water bodies, including small and shallow ones. Distance to a crayfish source was the single predictor variable explaining crayfish occurrence in most types of habitats and in both areas. The only exception was for the Sado permanent stream points, where crayfish presence was negatively affected by an interaction between elevation and flow velocity. Other habitat characteristics have apparently little or no importance for its successful colonization. Moreover, this study indicated that overland dispersal is apparently a frequent phenomenon in this species. Our findings can be used to determine which habitats are most likely to be colonized by the crayfish and to develop practical measures which may limit its spread and minimize its impacts.

Vulnerability of Southwest Iberian amphibians to an introduced crayfish, Procambarus clarkii

The introduction of predators in amphibian breeding habitats may contribute to the decline or extinction of amphibian populations. Procambarus clarkii , a North American crayfish, was recently introduced in the Iberian Peninsula, being now quite abundant in the southwest, a region with no native crayfish species and where 13 amphibian species may be found. We performed mesocosm experiments to evaluate the vulnerability of amphibian embryos and larvae from those species to P. clarkii . Despite the presence of alternative food (vegetation and leaf litter), embryo survival in the presence of P. clarkii was low for all species except Bufo bufo . However, newly hatched B. bufo tadpoles were readily consumed. P. clarkii reduced larval survival in all species, with those species that in nature have few contacts with predators at the larval stage suffering the highest mortalities. Most larvae reduced their activity and/or altered microhabitat use in the presence of P. clarkii , but these behavioural modifications did not lead necessarily to a low vulnerability to predation.

Predation by an Exotic Crayfish, Procambarus clarkii, on Natterjack Toad, Bufo calamita, Embryos: Its Role on the Exclusion of this Amphibian from its Breeding Ponds

Abstract Procambarus clarkii, an American crayfish, was introduced in the SW Iberian Peninsula three decades ago. This region has no native crayfishes; therefore, P. clarkii constitutes a potential threat for the embryos and larvae of amphibians, which may lack evolved defenses against it. We assessed the effects of this crayfish on the Natterjack Toad, Bufo calamita, using two complementary approaches. First, we studied the effect of crayfish presence on B. calamita breeding habitat use in temporary ponds of Doñana Natural Park (southwestern Spain). We surveyed 31 temporary ponds for the presence of P. clarkii and B. calamita eggs and tadpoles, and we conducted a logistic regression to determine if crayfish were significantly associated with Natterjack Toad distribution after habitat variables were taken into account. Second, we experimentally evaluated the impact of P. clarkii on B. calamita embryos in natural ponds with a two × two factorial experiment, using two ponds (one with and one without crayfish) and two treatments (embryos exposed or not exposed to predators). Crayfish presence was a negative predictor of B. calamita breeding habitat use; co-occurrence of the two species was limited to only one pond. Moreover, the predation experiment showed that survival of B. calamita embryos was strikingly reduced when they were directly exposed to crayfish compared to survival in all other treatments. Our results indicated that P. clarkii has a strong effect on B. calamita reproductive success and that it may play an important role in structuring amphibian communities in temporary ponds.

Assessing the landscape functional connectivity using movement maps: a case study with endemic Azorean insects

There is a vast body of literature aiming to predict, for a large number of taxa, the spatial distribution of suitable areas given the expected future changes of climatic conditions. However, such studies often overlook the role of landscape functional connectivity. This is particularly relevant for species with low vagility, as ground-dwelling insects, inhabiting areas with high human pressure due to habitat destruction and fragmentation, namely in the islands. In this study, we developed an individual-based model (IBM) that simulates individual movement according to landscape resistance and mortality probability, in order to derive the landscape movement map, and applied it to five endemic ground-dwelling insects of Terceira Island (Azores). We then confronted the movement maps of each species against the species distribution models previously developed for both current and future climatic conditions, quantifying the amount of important movement areas that are enclosed by the distribution polygons. We further sought to identify where habitat restoration would increase the overall connectivity among large habitat patches. Our results showed that, for both timeframes, the distribution models enclosed small amounts of areas predicted to be important for animal movement. Additionally, we predicted strong reductions (up to 94%) of these important areas for functional connectivity. We also identified areas in-between native forest of primary importance for restoration that may significantly increase the probability of persistence of our model species. We anticipate that this study will be useful to both conservation planners and ecologists seeking to understand species movement and dispersal both is islands and elsewhere.