Elevational gradients and species richness: do methods change pattern perception?

Aim Species richness patterns along elevational gradients have been documented extensively. Yet, the implications of differences in how the data are compiled are seldom explored. We investigate the effect of grain size on the richness–elevation relationship. Grain size varies among the principal methods used to collect or aggregate species occurrences: localized sites, elevational ‘bins’ and interpolation of species ranges. Assumptions of sampling and species distributions also vary among these methods. Methodology can influence the pattern that is perceived and comparability of results. We compare patterns from all three methods explicitly using the same suite of observations, based on museum records and field surveys of non‐flying small mammals. Our assessment is enhanced by comparing patterns resulting from each method for each of six adjacent mountain ranges. Location Utah, North America. Methods We document elevational species richness patterns using generalized linear models (GLMs), comparing the general shape of the trend as well as curvature, location and magnitude of peak richness across methods, both within and among gradients. We also introduce a new procedure to test for richness peaks using site‐based occurrences. Results We find a general congruence of the richness–elevation relationship, depicting a hump‐shaped pattern with a second‐order polynomial GLM showing a significant fit to nearly all gradient‐methodology combinations. However, underlying characteristics of the trend may vary with grain size. As grain size coarsens, maximum species richness increases and elevation of the mode slightly decreases. Results for curvature vary, but degree of curvature tends to increase as grain size coarsens. The richness–elevation patterns are independent of sampling effects. Main conclusions The perceived elevational diversity pattern for small mammals along these mountain ranges is not scale‐dependent. Differences in how the data are compiled are not reflected in major differences in patterns, even when local samples are neither uniformly spaced nor sampled with the same intensity. This result lends confidence to the assertion that patterns documented in similar studies with different methodologies and for which sampling is sufficiently comprehensive are good indicators of diversity. However, consistency of results from more than one compilation method may help to address issues of scale‐dependence, more so when these comparisons are made explicit.     

Relationships between abundance and body size: where do tourists fit?

Abstract.

• 1 The possible effects of the inclusion of ‘tourist’ species have been the cause of some concern in investigations of interspecific relationships between abundance and body size.
• 2 Data for adult beetles (Coleoptera) from oak trees in Britain are used to investigate the relationship of abundance to body size when tourists are and are not included.
• 3 For this particular assemblage, tourists do not fundamentally alter the basic statistics of the relationship between abundance and body size. However, they are not a random sample of the beetle assemblage. They have lower abundances and are also of smaller body size than other species.

     

Untangling interactions: do temperature and habitat fragmentation gradients simultaneously impact biotic relationships?

Gaining insight into the impact of anthropogenic change on ecosystems requires investigation into interdependencies between multiple drivers of ecological change and multiple biotic responses. Global environmental change drivers can act simultaneously to impact the abundance and diversity of biota, but few studies have also measured the impact across trophic levels. We firstly investigated whether climate (using temperature differences across a latitudinal gradient as a surrogate) interacts with habitat fragmentation (measured according to fragment area and distance to habitat edges) to impact a New Zealand tri-trophic food chain (plant, herbivore and natural enemy). Secondly, we examined how these interactions might differentially impact both the density and biotic processes of species at each of the three trophic levels. We found evidence to suggest that these drivers act non-additively across trophic levels. The nature of these interactions however varied: location synergistically interacted with fragmentation measures to exacerbate the detrimental effects on consumer density; and antagonistically interacted to ameliorate the impact on plant density and on the interactions between trophic levels (herbivory and parasitoid attack rate). Our findings indicate that the ecological consequences of multiple global change drivers are strongly interactive and vary according to the trophic level studied and whether density or ecological processes are investigated.     

Growth factors: a role in guiding axons?

A remarkable finding to emerge in recent years is that the early brain neuroepithelium is highly patterned before axonogenesis begins. Growth factors are among a variety of classes of molecules whose regionalized expression divides the early brain into molecularly distinct domains. Thus, when axons first grow to their synaptic targets, growth factor signalling may help them to navigate. This review discusses recent studies that reveal that growth factors can act as chemoattractants and repellents and that growth factor signalling is important for target entry. These new findings raise the compelling idea that growth factors play an active role in axon navigation.     

Habitat selection and ranges of tolerance: how do species differ beyond critical thresholds?

Sensitivity to habitat fragmentation often has been examined in terms of thresholds in landscape composition at which a species is likely to occur. Observed thresholds often have been low or absent, however, leaving much unexplained about habitat selection beyond initial thresholds of occurrence, even for species with strong habitat preferences. We examined responses to varying amounts of tree cover, a widely influential measure of habitat loss, for 40 woodland bird species in a mixed woodland/grassland landscape in eastern North Dakota, USA. We used LOESS smoothing to describe incidence for each species at three scales: within 200, 400, and 1200 m around sample locations. For the 200‐m scale, we also calculated the most‐preferred range of tree cover (within which at least half of observations were predicted to occur) for each species. Only 10 of 40 species had occurrence thresholds greater than about 10% tree cover. After initial occurrence, species showed three general patterns: some increased monotonically with tree cover; some increased up to an asymptote; some peaked at intermediate amounts of tree cover and then declined. These patterns approximate selection for interior woodlands and for edge‐rich environments, but incidence plots provide greater detail in landscape‐scale selection than do those categories. For most species, patterns persisted at larger scales, but for some, larger scales had distinctly different patterns than local scales. Preferred ranges of tree cover varied from <20% tree cover (common grackle, Quiscalus quiscula) to >60% (veery, Catharus fuscescens). We conclude that incidence patterns provide more information on habitat selection than do threshold measures for most species: in particular, they differentiate species preferring concentrated woodlands from those preferring mixed landscapes, and they show contrasting degrees of selectiveness. [Correction added on 16 October 2012, after first online publication: the Abstract section has been reworded].     

Free-feeding insect herbivores along environmental gradients in Serra do Cipó: basis for a management plan

The distribution of free-feeding insect herbivores in Brazilian savanna was studied in the National Park of Serra do Cipó. Insect samples were obtained with sweep nets across cerrado (savanna), rupestrian field and altitudinal grassland vegetation from 800 to 1500 m above sea level. We found a low species richness in xeric and mesic habitats during both wet and dry seasons. Sap-sucking insects were the most abundant guild (53.4%) with Cicadellidae the most abundant family (27.2%). The hypothesis that taxon richness of free-feeding insects decreases with increasing altitude was supported in xeric habitats during the wet season only, mainly as a function of mountain summit effect. There was a decrease of 65% in the number of families occurring at 1400 and 1500 m compared with lower elevations. The exclusion of sites of rupestrian vegetation at mid-elevations from the analysis increased significantly the proportion of variance explained by the model. An examination of taxon distribution using canonical variate analysis supported this result. The hypothesis that mesic habitats are richer in species of free-feeding insect herbivores than are xeric habitats was not supported. The data indicate that plant sclerophylly may exert a strong negative influence on insect species richness, and that variation due to particular characteristics of each site strongly affected the studied guilds. The present results should inform conservation strategies for the National Park Management Plan, which is currently being developed. © Rapid Science Ltd. 1998     

Wnts as morphogens? The view from the wing of Drosophila

Morphogens are diffusible signalling molecules that pattern cellular fields by setting up differential gene expression in a concentration-dependent manner. Members of the Wnt family of signalling molecules are generally considered to be classical morphogens. However, a close analysis of their activity indicates that they do not fulfil all of the critera that are associated with the classical definition.     

Latitudinal gradients in butterfly body sizes: is there a general pattern?

We tested for the existence of latitudinal gradients in the body sizes of butterflies in North America, Europe, Australia and the Afrotropics. We initially compared body sizes (measured as male forewing length) of all butterflies found in 5° latitudinal bands in each region, and then evaluated the relationship between body size and latitude statistically using the latitudinal midpoint of each species' distribution. Trends were examined for species in all butterfly families together and for each family separately. We found that gradients in body sizes were inconsistent in different geographical regions and butterfly families; in some cases species were larger towards the tropics, in some they were smaller, and in other cases there were no relationships. Most of the gradients, when they existed, reflected between-family effects arising from changes in the relative numbers of species in each family across regions. We conclude that general ecological explanations for geographical trends in butterfly body sizes are inappropriate, and gradients largely reflect historical patterns of speciation within and between taxa in each biogeographical realm. Thus, the robustness of body size gradients found in other insect groups should be confirmed in future studies by including more than one geographical region whenever possible.     

Professional burnout as the state and process--what to do?

The professional staff in human service institutions is often required to spend time in intense involvement with other people. Frequently, the staff-client interaction is centred around the client's current problems (psychological, social, and/ or physical) and is therefore charged with feelings of anger, embarrassment, fear or despair In this article we follow the burnout which could not be only the consequence of such job characteristics but could appear also as the result of type of work organization, social relationships, and some bodies personal characteristics as life style, too. Moreover, it can be a consequence of a disturbed balance between give and take at all three levels of social exchange--at interpersonal, at the team, and at the organizational level. So burnout is not only the problem of individuals but also the problem of social environment in which they work. The workplaces shape how people interact with another and how they carry out their jobs. In addition, we try to find the ways how to prevent or to reduce burnout, too. So we present the theories of social comparison (Festinger, 1954; Schachter, 1959), equity theory (Walster and Berscheid, 1978), as also the Kahn's model of employee engagement (1990) and the Schaufeli- Buunk's integrative comprehensive social exchange model (1993) as the possible key to help individuals and organization. In this context V. also Frankl's logo therapy (sense of purpose, 1960) became much more important as the theories of positive (Seligman, 2000) and humanistic psychology (Maslow, 1971, 1987; Rogers, 1959), too.     

Over the top: do thermal barriers along elevation gradients limit biotic similarity?

Organismal dispersal through mountain passes should be more constrained by temperature‐related differences between lowland and highland sites in montane environments. This may lead to higher rates of diversification through isolation of existing lineages toward the tropics. This mechanism, proposed by Janzen, could influence broad‐scale patterns of biodiversity across mountainous regions and more broadly across latitudinal gradients. We constructed two complementary analyses to test this hypothesis. First, we measured topographically‐derived thermal gradients using recently‐developed climatic data across the Americas, reviewing the main expectations from Janzen's climatic model. Then, we evaluated whether thermal barriers predict assemblage similarity for amphibians and mammals along elevational gradients across most of their latitudinal extent in the Americas. Thermal barriers between low and high elevation areas, initially proposed to be unique to tropical environments, are comparably strong in some temperate regions, particularly along the western slopes of North American dividing ranges. Biotic similarity for both mammals and amphibians decreases between sites that are separated by elevation‐related thermal barriers. That is, the stronger the thermal barrier separating pairs of sites across the latitudinal gradient, the lower the similarity of their species assemblages. Thermal barriers explain 10–35% of the variation in latitudinal gradients of biotic similarity, effects that were stronger in comparisons of sites at high elevations. Mammals' stronger dispersal capacities and homeothermy may explain weaker effects of thermal barriers on gradients of assemblage similarity than among amphibians. Understanding how temperature gradients have shaped gradients of montane biological diversity in the past will improve understanding of how changing environments may affect them in the future.     

Blue tail and striped body: why do lizards change their infant costume when growing up?

Ontogenetic changes in color and pattern that are not directlyrelated to reproduction are very common yet remain a poorlyunderstood phenomenon. One example is conspicuous colors inthe tails of fish, amphibians, and reptiles that fade out laterin life. We suggest a novel hypothesis: conspicuous tail colorsthat appear only in juveniles compensate for an increased activitylevel, deflecting imminent attacks to the tail. We observedblue-tailed, newly hatched lizards (Acanthodactylus beershebensis)in the field and compared 5 behavioral parameters with thoseof older individuals that had already lost their neonate coloration.In addition, we explored whether tail displays, often assumedto direct a predator's attention to the tail, disappear withthe color change. Striped blue-tailed hatchlings foraged moreactively than 3-week-old juveniles, spent a longer time in openmicrohabitats, and performed deflective tail displays. In comparison,2 other lacertids that do not undergo ontogenetic change didnot switch to safer foraging when growing up. The results suggestthat activity alteration may be a major factor affecting theontogenetic color and pattern change. Active lizards that foragein open habitats increase their probability of attack by ambushpredators. Conspicuous colors and deflection displays may shiftattacks to the expendable tail, increasing the prey's overallprobability of surviving attacks. The persistence of both stripedbody pattern and blue tail fits the active foraging period ofneonates and hence may be appropriate for other species thatdisplay a conspicuous tail accompanied by a striped pattern.