Martha Yanez

Bio: Martha Yanez is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Courtship display & Endangered species. The author has an hindex of 2, co-authored 2 publications receiving 91 citations.

Spatial distribution and habitat preference of the endangered tarantula, Brachypelma klaasi (Araneae: Theraphosidae) in Mexico

Abstract: Brachypelma, a genus of nine endangered tarantula species in Mexico, is the only group of spiders included in Appendix II of CITES, owing to habitat degradation and illegal trafficking. However, while the majority of the nine species of Brachypelma are thought to be threatened, little is known of their ecology and distribution. Brachypelma klaasi is the rarest species, occurring in a few isolated populations on the Pacific coast of Mexico. We present an analysis of population distribution and micro-habitat requirements of B. klaasi over different spatial scales within the biological reserve at Chamela, Jalisco as part of a wider ecological study of the endangered Brachypelma group. Burrows and dispersing spiders were confined to a southern area of the reserve covering approximately 0.5 km2. Within this area, burrows were not aggregated at lower spatial scales (24–216 m2), unlike other related species. Also, there was no evidence that intra-specific interactions (either positive or negative interactions) influenced the distribution of burrows. Distribution of burrows at low spatial scales was related to low afternoon temperatures and high humidity in mid-summer. These abiotic factors may influence the survival and development of eggs and spiderlings, and appear to be more important in governing the distribution of B. klaasi than are food resources or intra-specific interactions. We discuss how these findings may facilitate the re-introduction of captive-bred individuals of B. klaasi and other Brachypelma species.

Courtship and mating behavior of brachypelma klaasi (araneae, theraphosidae)

Abstract: Courtship and mating behavior of Brachypelma klaasi, heretofore unknown, is described on the basis of three courtship and mating sequences, one in captivity and two in the field. Adult males perform courtship movements (pedipalp drumming, leg drumming, push-up and shaking) when they locate a female's burrow, probably in order to avoid female aggression. After some physical contact, the female raises the prosoma and extends her chelicerae. The male then grasps her chelicerae with his tibial apophyses and the female arches her body backwards leaving the epigynum exposed. The male starts boxing the female's sternum and presumably inserts his pedipalps and inseminates the female. In two cases the female vigorously attacked the male immediately after mating and probably would have killed him had observers not intervened; the other pair separated more slowly and peacefully. Males appear to use chemical and/or tactile cues from the female's silk around the burrow during short-range searching behavior. Males begin courtship behavior by drumming on the silk to signal to the female that he is present. One male of B. klaasi observed in the held laid silk over the female's silk around the burrow, possibly to prevent subsequent matings by other males. A second male did not detect the burrow after this act.

Evaluating presence-absence models in ecology: the need to account for prevalence

Abstract: • 1. Models for predicting the distribution of organisms from environmental data are widespread in ecology and conservation biology. Their performance is invariably evaluated from the percentage success at predicting occurrence at test locations. • 2. Using logistic regression with real data from 34 families of aquatic invertebrates in 180 Himalayan streams, we illustrate how this widespread measure of predictive accuracy is affected systematically by the prevalence (i.e. the frequency of occurrence) of the target organism. Many evaluations of presence–absence models by ecologists are inherently misleading. • 3. With the same invertebrate models, we examined alternative performance measures used in remote sensing and medical diagnostics. We particularly explored receiver-operating characteristic (ROC) plots, from which were derived (i) the area under each curve (AUC), considered an effective indicator of model performance independent of the threshold probability at which the presence of the target organism is accepted, and (ii) optimized probability thresholds that maximize the percentage of true absences and presences that are correctly identified. We also evaluated Cohen's kappa, a measure of the proportion of all possible cases of presence or absence that are predicted correctly after accounting for chance effects. • 4. AUC measures from ROC plots were independent of prevalence, but highly significantly correlated with the much more easily computed kappa. Moreover, when applied in predictive mode to test data, models with thresholds optimized by ROC erroneously overestimated true occurrence among scarcer organisms, often those of greatest conservation interest. We advocate caution in using ROC methods to optimize thresholds required for real prediction. • 5. Our strongest recommendation is that ecologists reduce their reliance on prediction success as a performance measure in presence–absence modelling. Cohen's kappa provides a simple, effective, standardized and appropriate statistic for evaluating or comparing presence–absence models, even those based on different statistical algorithms. None of the performance measures we examined tests the statistical significance of predictive accuracy, and we identify this as a priority area for research and development.

Reproductive biology of uruguayan theraphosids (araneae, mygalomorphae)

Abstract: We describe the reproductive biology of seven theraphosid species from Uruguay. Species under study include the Ischnocolinae Oligoxystre argentinense and the Theraphosinae Acanthoscurria suina, Eupalaestrus weijenberghi, Grammostola iheringi, G. mollicoma, Homoeomma uruguayenseand Plesiopelma longisternale. Sexual activity periods were estimated from the occurrence of walking adult males. Sperm induction was described from laboratory studies. Courtship and mating were also described from both field and laboratory observations. Oviposition and egg sac care were studied in the field and laboratory. Two complete cycles including female molting and copulation, egg sac construction and emer- gence of juveniles were reported for the first time in E. weijenberghi and O. argentinense. The life span of adults was studied and the whole life span was estimated up to 30 years in female G. mollicoma, which seems to be a record for spiders. A comprehensive review of literature on theraphosid reproductive biology was undertaken. In the discussion, we consider the lengthy and costly sperm induction, the widespread display by body vibrations of courting males, multiple mating strategies of both sexes and the absence of sexual cannibalism.

Modelling breeding habitat preferences of Bonelli’s eagle (Hieraaetus fasciatus) in relation to topography, disturbance, climate and land use at different spatial scales

Abstract: Predictive models on breeding habitat preferences of Bonelli’s eagle (Hieraaetus fasciatus; Aves: Accipitridae) have been performed at four different spatial scales in Castellon province, East of Iberian Peninsula. The scales considered were: (1) nest site scale (1×1 km2 Universal Transverse Mercator (UTM) square containing the nest); (2) near nest environment (3×3 km2 UTM square); (3) home range scale (5×5 km2 UTM square); and (4) landscape level scale (9×9 km2 UTM square containing the above mentioned ones). Topographic, disturbance, climatic and land use factors were measured on a geographic information system (GIS) at occupied and unoccupied UTM squares. Logistic regression was performed by means of a stepwise addition procedure. We tested whether inclusion of new subset of variables improved the models by increasing the area under the receiver operator characteristic plot. At nest site scale, only topographic factors were considered as the most parsimonious predictors. Probability of species occurrence increases with slope in craggy areas at lower altitudes. At the 3×3 km2 scale, climate and disturbance variables were included. At home range and landscape level scales, models included climate, disturbance, topographic and land use factors. Higher temperatures in January, template ones in July, higher rainfall in June, lower altitudes and higher slope in the sample unit increase probability of occurrence of Bonelli’s eagle at broadest scales. The species seems to prefer disperse forests, scrubland and agricultural areas. From our results, we consider that there is a hierarchical framework on habitat selection procedure. We suggest that it is necessary to analyse what key factors are affecting Bonelli’s eagle nest-site selection at every study area to take steps to ensure appropriate conservation measures. The combination of regression modelling and GIS will become a powerful tool for biodiversity and conservation studies, taking into account that application depends on sampling design and the model assumptions of the statistical methods employed. Finally, predictive models obtained could be used for the efficient monitoring of this scarce species, to predict range expansions or identify suitable locations for reintroductions, and also to design protected areas and to help on wildlife management.