Tal Seifan

Recently, Mingo has analyzed the properties of I imp, an importance index, and demonstrated that its range is not symmetrical. While agreeing with this comment, we believe that more light needs to be shed on the issue of symmetry in relation to such indices. Importance indices are calculated using three values: performance of the organism in the absence and in the presence of neighbors and maximum performance of the organism in ideal conditions. Because of this structure, importance indices can hardly ever achieve symmetry along the whole range of potential performances. We discuss the limitation of the symmetry range for different symmetry types and for both additive and multiplicative indices. We conclude that importance indices, as other interactions indices, are practical tools for interpreting ecological outcomes, especially while comparing between studies. Nevertheless, the current structure of importance indices prevents symmetry along their whole range. While the lack of "perfect" symmetry may call for the development of more sophisticated importance metrics, the current indices are still helpful for the understanding of biological systems and should not be discarded before better alternatives are well established. To prevent potential confusion, we suggest that ecologists present the relevant index symmetry range in addition to their results, thus minimizing the probability of misinterpretation.

Disturbances are characteristic for many ecosystems. However, we still lack generalizations concerning their role in shaping communities, particularly when disturbances co-occur. To study such effects, we used a novel modeling approach that is unrestricted by a priori tradeoffs among specific plant traits, except for those generated by allocation principles. Thus, trait combinations were emergent properties associated with biotic and abiotic constraints. Specifically, we asked which traits dominate under specific disturbance regimes, whether single and combined disturbance regimes promote similar trait tradeoffs and how complex disturbance regimes affect species richness and functional diversity. Overall, disturbances' temporal properties governed the outcome of combined disturbances and were a stronger assortative force than spatial disturbance properties: low temporal predictability decreased seed-dispersability and dormancy, but increased competitive ability and disturbance tolerance. Evidence for tradeoffs between different colonization modes and between dormancy and disturbance tolerance were found, while surprisingly, the widely accepted colonization-competition tradeoff was not generated. Diversity was highest at intermediate disturbance intensity, but decreased monotonically with increasing unpredictability. In accordance with our results, future models should avoid restrictive assumptions about tradeoffs to generate robust and more general predictions about the role of disturbances for community dynamics. (C) 2011 Elsevier GmbH. All rights reserved.

This report, derived mainly from intensive observations of Gonatodes humeralis (on trees) on Trinidad and G. ocellatus (in culverts) on Tobago, islands of the West Indies, in May-June, 2000. It shows that these geckos are sit-and-wait foragers that prefer a perch posture with the head pointing down, irrespective of the height above the ground. This posture apparently enables better detection of better-illuminated prey. The height of the gecko above ground and its posture were not significantly affected by temperature or light. The coincidence of captive geckos dying when sloughing is discussed. Locality records presented include G. ocellatus horn a new locality in Tobago, the Tobago mountains at approx.11[degree]17[minute]N, 60[degree]36 [minute] W, altitude 460m. An additional, as yet unreported, species of Gonatodes may occur on Tobago.

Gonatodes vittatus was observed in Trinidad, both in the field and in captivity. In the field it occurred on trees and masonry walls, and on and inside wooden houses. At least some individuals showed great site fidelity to their retreats. Males and females were territorial; in captivity males required about twice the area that females did, and in the field the sex ratio (males:females) varied from 50:100 to 71:100. The natural life span was at least 3 years. In houses, the predators of G. vittatus included the larger gecko species; and in captivity, death sometimes accompanied faulty moulting (sloughing). The diel cycle was characteristically diurnal, and emergence was temperature-dependent. G. vittatus is a sit-and-wait forager, and individuals preferred a vertical perch posture with the head pointing down, irrespective of the height above the ground. At night, some individuals living in protected areas slept on the walls in the open. New locality records for G. vittatus include one in north-eastern Tobago at 11[degree] 18[minute] 50[second]N, 60[degree] 32[minute] 30[second] W.