Resumen de Development of biomonitoring methods in birds for the study of ecological traps associated to environmental pollutants
Animals can select habitat according to cues of the environment that they associate with better survival and reproductive success, however, if an environment changes suddenly, the normal cues might no longer correlate with the expected outcome and as a result, the animals may be involved in an ecological trap. An ecological trap as a situation in which organisms prefer a low-quality habitat over superior habitats. This trap can lead to extinction if a population falls below a critical size threshold before adaptation to the novel environment occurs.
In this thesis, I evaluated presence of the ecological traps for wildlife driven by pollutants in two scenarios that may affect a great number of wildlife: (Scenario 1) wetlands receiving effluents of wastewater treatment plants (WWTP), which are highly productive habitats for many bird species; and (Scenario 2) habitats with high densities of rodents and an intensive use of anticoagulant rodenticides, which can attract and poison several species of predatory birds and mammals.
To achieve these goals, firstly (scenario 1) I evaluated the presence and concentration of environmental pollutants in sediment and in blood, feathers and preen oil of common moorhens (Gallinula chloropus) from Navaseca Pond, which receives directly the effluent of a WWTP; and from Tablas de Daimiel National Park (TDNP), which is a floodplain less affected by urban discharges. In addition changes on physiological and biochemical biomarkers were also studied. In scenario 2, I studied the prevalence and levels of anticoagulant rodenticides (ARs) in non-target species of wildlife and the environmental factors that influence such exposure.
In the scenario 1, samples of sediment from Navaseca Pond had concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb higher than sediments from TDNP; only Se was higher in TDNP than in Navaseca Pond possibly by the presence of seleniferous soil in the basin. Regarding to biological samples of common moorhens, blood levels of Hg and Se were higher in moorhens from TDNP than those from Navaseca Pond and 24.4% of moorhens exhibited levels of Se above the threshold value associated with Se toxicity in birds. In feathers, Hg, Se, Mn, Cu and As levels were higher in TDNP than in Navaseca Pond. PCBs and p,p'-DDE were found in 32% of the blood and 51% of preen oil samples of the moorhens and both types of compounds were higher in Navaseca Pond than in TDNP in both type of samples. These levels of OC's indicated no direct threat, because PCBs and p,p'-DDE were below any threshold described for effects on parental breeding behaviour or eggshell thinning.
Preen oil wax composition of moorhens was dominated by monoesters of 35 to 38 carbons and displayed a seasonal variation, in which long-chain waxes were more abundant during the breeding season, as an adaptation to reduce olfactory signals response to avoid predation by mammals. Moorhens in Navaseca Pond showed less marked seasonal variations in wax preen oil composition and sex hormone levels than in TDNP. Exposure to biotic and abiotic pollutants in Navaseca Pond can are causing an overexpression of the immune response and endocrine disruption in the common moorhens. This birds also exhibited a lowest lipid peroxidation, but also lower levels of circulating antioxidants and a greater activity of GPX, and the sum of the action of all these antioxidants defences could explain that less oxidative damage.
In scenario 2, second generation anticoagulant rodenticides (SGARs) were detected in non-target species, being bromadiolone, brodifacoum and flocoumafen the most frequent by their high capacity to bioaccumulate in liver tissue. Generalist and specialist species exhibited similar prevalence of ARs, but mammal predators showed the highest concentrations, possibly by their generalist diet including rodents. Although it is difficult to confirm the death by ARs poisoning, 23.3% (Chapter 5) and 37% (Chapter 6) of individuals had more than 200 ng/g of ARs in liver associated with adverse effects and in many cases this was accompanied by the presence of haemorrhages. The use ARs as biocides was determinant in the exposure of non-target species, and it was associated mainly with human density population, urbans areas and/or cattle farms, probably because the high density of commensal rodents found in these environments attracts predators to areas with intensive use of ARs.
Although the presence of an ecological trap driven for environmental pollutants was not fully demonstrated in the studied scenarios because of the lack of strong evidences of population effects, I have contributed in the development of a rationale for the work within the ecological trap framework in the field of ecotoxicology.
