Summary 1.Understanding and predicting the form of species distributions, or occupancy patterns, is fundamental to macroecology and is dependent on the identification of scaling relationships that underlie the patterns observed. 2. Occupancy-abundance models based on the negative binomial distribution and Taylor's power law are spatially implicit, rather than explicit, as they include no information on the relative positions of individuals. Here we present a spatially explicit model, the spatial scaling occupancy (SSO) model, to estimate species occupancy and spatial correlation, based on join-count statistics, or a pair approximation, approach. This model provides a spatially explicit description of species range size and aspects of range structure. 3. Occupancy data from Drosophilidae species inhabiting a decaying fruit mesocosm were used to test the SSO model. Predictions from the spatially implicit and explicit models were largely equally accurate. The SSO model is thus more efficient as it is less data demanding, and more informative as it provides an estimation of spatial correlation. 4.The results also showed that species distribution patterns differ when examined with spatially implicit vs. explicit approaches; the scaling relationship between occupancy and local density identifies a focal grain for studying the scale-dependent nature of ecological relationships; and the longer the length of the sample edge, the higher the occupancy observed under conditions of spatial aggregation. 5. The SSO model presents a step towards a general scaling model for occupancy, and demonstrates that the inclusion of spatially explicit information in macroecological models warrants further attention.

pollinator (Ceratosolen galili) has been reported to be rarer than the pollinator (Ceratosolen arabicus) in drier areas due to lower desiccation tolerance. Both species are closely related and utilise the same oviposition sites on Ficus sycomorus. We used ecological niche modelling to determine whether C. galili covers the range of F. sycomorus and whether it is consistently rarer than C. arabicus. We examined emergence times, critical thermal limits, desiccation and starvation tolerances of the wasps. The suggested rarity of C. galili relates to lower abundance in certain months and at certain localities but a similar number of occurrence records within the distributional range (except in arid regions, e.g. Namibia). In contrast to C. galili, C. arabicus has a wider thermal range, lives longer under hydrating and dehydrating conditions and is a nocturnal flier. The synergistic effect of physiological tolerances and flight time differences exacerbate the less favourable conditions available to C. galili during flight and location of receptive figs. These factors enable C. arabicus to survive for longer than C. galili, meaning that they are more likely to disperse to trees that are flowering further away in space and time.Combining correlative and mechanistic approaches has aided us in understanding the ecological niches of these species. 3Physiology, species abundance patterns and distribution A complex and varied set of factors may determine the range limits of a species, and the abundance structure across its range. Fine-scale changes in the distribution of suitable microclimates may lead to changes in population size and colonization rate and to changes in distribution (Wilson et al. 2009). The physiological tolerances of species may be one driver of has become a model system for investigating numerous evolutionary and ecological questions (Janzen 1979, Wiebes 1979, Wang et al. 2008. In these mutualisms, the tree depends on the wasp for the dispersal of pollen and for seed set, while the wasp depends on the tree for offspring development (Wang et al. 2008).In contrast to externally feeding insects, fig wasp pollinators are expected to occupy most of the geographical ranges of their hosts because of their intimate host associations (Wiebes 1979, Weiblen 2002. A shift in the host's distribution must entail a concomitant shift in the distribution of the pollinator for the mutualism to persist and vice-versa. If the host plant becomes extinct, the wasp will also become extinct unless it is able to shift to a new host plant. A species that has a greater starvation tolerance would be able to search for longer (i.e. able to resist starvation for longer) and would be more likely to find a suitable host (see also Kjellberg et al. 1988).In addition, the wasps may be more susceptible to unfavourable environmental conditions at certain times of the day. For example, a temporal structuring of emergence times may allow nocturnally emerging individuals to survive unfavourable seasons while diurnally emerging individuals suc...

Summary 1.The ubiquitous, positive abundance-occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures. 2. He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field-based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit. 3. With individual (and groups of ) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He-Gaston model differed significantly from measured values, and were least accurate for the most abundant species. 4. Substitution of k -values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k -values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions. 5. Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He-Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit. 6. Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard.

Ever since Darwin's discovery of natural selection, we expect traits to evolve to increase organisms' fitness. As a result, we can use optimization models to make a priori predictions of phenotypic variation, even when selection is frequency-dependent. A notable example is the prediction of female-biased sex ratios resulting from local mate competition (LMC) and inbreeding. LMC models incorporate the effects of LMC and inbreeding. Fig wasp sex ratio adjustments fit LMC predictions well. However, the appropriateness of LMC models to fig wasps has been questioned, and the role that a coincidental by-product plays in creating the apparent fit has been clearly illustrated. Here, we show that the sex ratio adjustments of a fig wasp are the result of a dual mechanism. It consists of a standard facultative LMC response favoured by natural selection, as well as a mechanism that may be the result of selection, but that could also be a coincidental by-product. If it is a by-product, the fitness increase is coincidental and natural selection's role was limited to fine-tuning it for higher fitness returns. We further document a case of an apparent fitness-reducing sex ratio adjustment. We conclude that the use of the adaptationist approach demands that our understanding of traits must be remodelled continually to rectify spurious assumptions.

Body size is a major component of fitness. However, the relative contributions of different factors to optimal size, and the determinants of spatial and temporal variation in size, have not been fully established empirically. Here, we use a mesocosm of a Drosophilidae assemblage inhabiting decaying nectarines to investigate the influence of spatial variation in temperature on adult body size in Drosophila simulans Sturtevant. Two treatments were established; one in the sun where developing larvae were exposed to high temperatures and the other in the shade where temperature conditions were milder. The simple developmental effects of temperature differences (i.e. larger flies are likely to emerge from cooler environments), or the simple effects of stressful temperatures (i.e. high temperatures yield wing abnormalities and smaller flies), were overridden by interactive effects between temperature and larval density. Emergences were lower in the sun than shade, probably as a result of temperature-induced mortality. However, flies attained the same final sizes in the shade and sun. In addition, abnormally winged flies were clustered in the shaded treatments. In the shade treatments, where emergences were higher than in the sun, stressful conditions as a result of high larval density likely resulted in wing abnormalities and small size. Consequently, there was little spatial variation in size across the mesocosm, but substantial spatial variation in abundance. Under natural conditions both mortality and non-lethal effects of temperature and/or crowding are likely to play a role in the evolution of body size.