Judging Survey Quality: Local Variances

The present study was undertaken to explore possibilities to judge survey quality on basis of a limited and restricted number of a-priori observations. Here, quality is defined as the ratio between survey and local variance (signal-to-noiseratio). The results indicate that the presented surveys do not permit such judgement. Furthermore, the discussion alsosuggests that the 5-fold local sampling strategies do not merit any sound judgement in about 10% of all cases.The results further imply that surveys will benefit from procedures, controls and approaches in sampling and sample handling, to assess both average, variance and the nature of the distribution of elemental concentrations in local sites. This reasoning is compatible with the idea of the site as a basic homogeneous survey unit, which is implicitly and conceptually underlying any survey performed.     

The evolution of leks through female choice: differential clustering and space utilization in six sympatric manakins

Summary The degree to which lekking and non-lekking male manakins select display sites in order to maximise proximity to females was examined by contrasting movements of females with male dispersion. Data on female visiting patterns, male courtship disruption, and mating skew were also collected over three successive breeding seasons. For the five lek-breeding species, female home-ranges were 3–7 times larger than those of adult males. Female movements were concentrated around leks, fruiting places and stream bathing sites. None of the females monitored by radio-tracking expanded her normal range in order to visit males on leks. On the contrary, feeding bouts of females frequently preceded a visit to potential mates at neighboring leks. Despite small sample sizes, significant correlations were found between female home-range size and male clustering (distances between neighboring leks and distances between neighboring males), as predicted by the female choice model and the hotspot model. Adult and immature male home-range sizes were not significantly correlated with male dispersion or female ranges. On the other hand, males and females of the only non-lekking species exhibited similar use of space and home-range size. Male settlement at sites with high levels of female traffic showed that the hotspot model is adequate to explain differences in male dispersion among sympatric lekking species. Comparisons with other studies suggest that apparent female choice could be overidden by past and present male-male interactions or female mate-comparison tactics. In fact, both the hotspot model and the attractiveness hypothesis appear to shape male dispersion on leks: males appear to settle under hotspot conditions with despotic rules generated through bias in female choice or male-male interference. It is proposed that the evolution of leks is ecologically motivated by the spatio-temporal distribution of trophic resources, initially leading to a dispersed male-advertisement polygyny. Following this, a foraging ecology that promotes high mobility by females and the magnetic effect of mating skew in particular males may have favored clustering on exploded leks. Later, the development of male-male interference and the increasing female home-range size could have led to the evolution of classical leks.     

Relations between sulphate,ammonia, nitrate,acidity and trace element concentrations in tree bark in The Netherlands

Bark flakes were sampled in a biomonitoring survey throughout The Netherlands. Tree species used were oak (65 samples) and non-oak (58 samples) (poplar, elm, willow). Bark elemental analysis was carried out for As, Br, Ca, Cd, Ce, Co, Cr, Cs, Fe, Hg, K, La, Na, Ni, Pb, Rb, Sb, Sc, Se, Sm, Th, and Zn. Furthermore, bark acidity, SO₄, NH₄ and NO₃ were determined. Further variables introduced into the data-set were DIST (closest distance to sea water) and the dummy variably OAK (tree species).Straightforward multivariate correlation analysis was performed to check the effects on bark metal retention of the non-metal pollutants SO₄, NH₄ and NO₃, and of bark acidity. The OAK variable served to identify species-specific metal and non-metal pollutant behaviour. The DIST variable was used to visualize geography(source)-related variations in bark metal and non-metal pollutant concentrations, and to account for the non-random distribution of OAK and non-OAK tree species.The results indicate that the non-oak and oak bark samples may be combined to form 123 samples containing data-set for As, Br, Cd, Ce, Co, Fe, La, Na, Sc, Sm, Th, Zn, NH₄, NO₄, SO₄ and acidity, but not for Rb, Cs, Se, K, Ni, Pb and Sb (species-specific) and for Ca and Hg (H⁺-dependent). In the presented data-set, bark sulphate, ammonia and nitrate could not be shown to significantly affect bark metal retention.     

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