Changes in Species Richness,Abundance, and Composition of Arboreal Twig‐nesting Ants Along an Elevational Gradient in Coffee Landscapes

The distribution, diversity, and assembly of tropical insects have long intrigued ecologists, and for tropical ants, can be affected by competitive interactions, microhabitat requirements, dispersal, and availability and diversity of nesting sites. Arboreal twig‐nesting ants are limited by the number of hollow twigs available, especially in intensive agricultural systems. Ant diversity and abundance may shift along elevation gradients, but no studies have examined if the proportion of occupied twigs or richness of arboreal twig‐nesting ants vary with elevation. In coffee agroecosystems, there are over 40 species of arboreal twig‐nesting ants. We examined communities of twig‐nesting ants in coffee plants along an elevational gradient to answer the following questions: (1) Do species richness and colony abundance decline with elevation or show a mid‐elevation peak? (2) Does community composition change with elevation? (3) Is elevation an important predictor of change in ant abundance, richness, and relative abundance of common species? We surveyed 42 10 × 10 m plots in 2013 from 450 to1550 m elevation across a coffee landscape in Chiapas, Mexico. We sampled a total of 2211 hollow coffee twigs, 77.1 percent of which were occupied by one of 28 species of ants. Pseudomyrmex simplex was more abundant in lower elevations, whereas Pseudomyrmex ejectus dominated in high elevations. Species richness and the percent of occupied hollow twigs both peaked at mid‐elevations (800–1050 m). In sum, we found that species richness, abundance, and composition of arboreal twig‐nesting ants shift with elevation. These findings may provide important insights for understanding ant communities in coffee agroecosystems.     

Beta‐diversity gradients of butterflies along productivity axes

Aim Several lines of evidence suggest that beta diversity, or dissimilarity in species composition, should increase with productivity: (1) the latitudinal species richness gradient is most closely related to productivity and associated latitudinal beta‐diversity relationships have been described, and (2) the scale dependence of the productivity–diversity relationship implies that there should be a positive productivity–beta‐diversity relationship. However, such a pattern has not yet been demonstrated at broad scales. We test if there is a gradient of increasing beta diversity with productivity. Location Canada. Methods Canada was clustered into regions of similar productivity regimes along three remotely sensed productivity axes (minimum and integrated annual productivity, seasonality of productivity) and elevation. The overall (β_j), turnover (β_sim) and nestedness (β_nes) components of beta diversity within each productivity regime were estimated with pairwise dissimilarity metrics and related to cluster productivity with partial linear regression and with spatial autoregression. Tests were performed for all species, productivity breadth‐based subsets (e.g. species occurring in many and a moderate number of productivity regimes), and pre‐ and post‐1970 butterfly records. Beta diversity between adjacent clusters along the productivity gradients was also evaluated. Results Within‐cluster β_j and β_sim increased with productivity and decreased with seasonality. The converse was true for β_nes. All species subsets responded similarly; however, productivity–beta‐diversity relationships were weaker for the post‐1970 temporal subset and strongest for species of moderate breadth. Between‐cluster beta diversity (β_j) and nestedness (β_nes) declined with productivity. Main conclusions As predicted, beta diversity of communities within productivity regimes was observed to increase with productivity. This pattern was driven largely by a gradient of species turnover. Therefore, beta diversity may make an important contribution to the broad‐scale gradient of species richness with productivity. However, this species richness gradient dominates regional beta diversity between productivity regimes, resulting in decreasing between‐productivity dissimilarity with productivity driven by a concurrent decline in nestedness.     

Differential elevational cline in the phenology and demography of two temporally isolated populations of a damselfly: Not two but one taxon?

1. Temporal isolation by cohort splitting is a life‐history mechanism that has been reported in many temperate insects, including those inhabiting freshwater habitats. Although the cohorts seem to maintain separate temporal niches in a specific location, the temporal isolation may be disrupted across a geographic gradient due to constraints imposed by seasonality. 2. This prediction was tested on two temporally isolated populations of the obligatory univoltine Lestes virens (Odonata, Lestidae) in north‐east Algeria. Although the two cohorts emerge at the same time in spring, one cohort reproduces in summer, while the second cohort estivates in summer and reproduces in autumn. A survey assessing the phenology and abundance was conducted on eight ponds across an elevational gradient (5–1012 m asl) using capture–mark–recapture and adult density sampling. 3. In all sites from low to high elevation, the species showed cohort splitting. The phenology of reproduction of both cohorts showed a delay with elevation, but the cline was 2.2 days for the summer cohort and 0.7 days for the autumn cohort per 100 m of elevation. Moreover, the density of adults in the autumn cohort was higher than that of summer cohort across the entire elevational range, and the difference increased with elevation. 4. These findings regarding the differential elevational cline in the phenology show that the temporal isolation of the two cohorts becomes narrower at high elevation, suggesting potential inter‐cohort temporal overlap at higher elevations. 5. The claim that the two cohorts of L. virens are true temporally isolated species needs further investigation.     

Ecological interactions among insect herbivores,ants and the host plant Baccharis dracunculifolia in a Brazilian mountain ecosystem

Insect–plant interactions occur in several ways and have considerable environmental and ecological importance. Many feeding strategies have evolved among herbivorous insects, with host–herbivore systems likely being influenced by trophobionts with ants. We investigated how these interactions vary across elevation gradients by evaluating the structure of the herbivorous insect community and ants associated with Baccharis dracunculifolia at three distinct elevations (800, 1100, and 1400 m a.s.l.) on a mountain in southeastern Brazil. Moreover, we evaluated the diversity and specialisation of interactions between herbivores and host plants along the elevational gradient. We sampled herbivores and ants on 60 plants at each elevation (totalling 180 plant individuals). Herbivore species composition differed among elevations, as did interaction diversity and specialisation. Richness and abundance of chewing insects increased with elevation, while β‐diversity among patches of the host plant was higher at the lowest elevation, probably due to the patchy occurrence of B. dracunculifolia. Richness and abundance of sap‐sucking insects were higher at the intermediate elevation, possibly due to local environmental conditions. We observed a positive relationship between ant and herbivore trophobiont richness on B. dracunculifolia. We found that interactions were more specialised and less diverse at higher elevations compared to the lowest elevation. Changes in vegetation and environmental variables shaped species distributions and their ecological interactions along the elevation gradient. Our study demonstrates that increased elevation changes the structure and patterns of interactions of the herbivore insect guilds associated with the host plant B. dracunculifolia. Ant effects depend on the context, the environment, and the species of ants involved, and are essential for the presence of insect trophobionts.     

Tropical tree species diversity in a mountain system in southern Mexico: local and regional patterns and determinant factors

Mechanisms explaining patterns of biodiversity along elevation gradients in tropical mountain systems remain controversial. We use a set of climatic, topographic, and soil variables encompassing regional, landscape, and local‐level spatial scales to explain the spatial variation of tree species diversity in the Sierra Madre of Chiapas, Mexico. We sampled 128 circular plots (0.1‐ha each) in four elevational bands along four elevation gradients or transects encompassing 100–2200 m. A total of 12,533 trees belonging to 444 species were recorded. Diversity patterns along the elevation gradient and the explanatory power of independent variables were dependent on spatial scale (regional vs transect) and functional group (total vs late‐successional or pioneer species). Diversity of all species and late‐successional species (1 – proportion of pioneer species) showed a constant pattern at the regional and transect scales, with low predictive power of climatic variables and/or elevation. A linear decrease in either number or proportion of pioneer species diversity was observed with increasing elevation, which was correlated with temperature, rainfall, and human disturbance trends. Total species diversity showed an increase with rainfall of the warmest quarter, indicating a regional‐level limiting effect of seasonality (drought duration). Yet the explanatory power of climatic and topographic variables was higher at the individual transect level than at the regional scale, suggesting the parallel but differential influence of evolutionary and geological history factors on diversification not so far studied to explain elevation patterns of species diversity in tropical mountain systems.     

Are plant pathogen populations adapted for encounter with their host? A case study of phenological synchrony between oak and an obligate fungal parasite along an altitudinal gradient

Biotrophic fungal pathogens are expected to have adapted to their host plants for phenological synchrony, to optimize the possibility of contacts leading to infections. We investigated the patterns and causes of variation in phenological synchrony in the oak‐powdery mildew pathosystem, a major disease in natural ecosystems. The study was carried out along an altitudinal gradient, representing a wide temperature range, in mature oak stands. Both sporulation (pathogen infective stage) and oak flushing (host susceptible stage) were delayed with increasing elevation, but with a significantly different sensitivity for the two species. This resulted in a variable host–pathogen synchrony along the gradient. A common garden experiment did not give evidence of among‐population genetic differentiation (past adaptation) for fungal phenology. This could be explained by the high phenotypic variation in phenology within host populations, precluding selection on fungal phenology at the population scale, but possibly favouring adaptation at the within‐population scale. Phenotypic plasticity was the major cause of the observed variation in the phenology of the fungal populations.     

Floristic variation,chorological types and diversity: do they correspond at broad and local scales?

Abstract. The relationships between biogeographical patterns and local‐scale patterns based on microscale features, such as topoclimate, are well known in plant biogeography. Here we present a method of determining this correspondence using constrained ordination and correlations. We examined compositional gradients at two different scales, biogeographical chorotypes, and diversity. Compositional data (124 taxa × 113 plots) were sampled at four regularly spaced sites in south‐eastern Spain. Longitude (LONGI) was used as a spatial variable representing an east–west climate gradient, together with a radiation index (RADIN), elevation, and a disturbance indicator. All factors correlated with the compositional gradients, but the local‐topoclimate factor (RADIN) and the broad‐scale factor (LONGI) were most important. These two, spatially independent factors were both correlated with the two first ordination axes, and therefore should relate to the same general trend in species‐turnover. There was a significant Spearman's rank correlation between the species order along these two gradients. This is interpreted as an ecological self‐similar pattern, i.e. coenoclines repeating at different scales. A consistent order of species along local‐ and broad‐scale coenoclines may indicate that similar operational factors act at several scales, here related to moisture and temperature. The distribution of Mediterraneo–Macaronesian, Mediterraneo–Saharo–Arabian and Ibero–Maghribian species confirmed the correspondence between the broad‐ and local‐scale gradients. The former group decreases in number with increasing aridity along both gradients, whereas the two latter groups increase. A discordant pattern was found with south‐eastern Iberian endemics, but this may be explained by several of them being edaphic (saxicolous) specialists. There is a significant decrease in species richness with high radiation, but the expected increase along the longitudinal gradient from west (dry) to east (moist) was not statistically significant. This may be due to the correspondence between high richness and disturbance, both occurring in the middle of the broad‐scale gradient.     

Aquatic insect β‐diversity is not dependent on elevation in Southern Rocky Mountain streams

相似文献   

The environmental control of plant species density on a Himalayan elevation gradient

Aim In eastern Nepal, forests occupy an elevation gradient of 4000 m with bioclimatic zones from near tropical to alpine. Understorey plants and trees were censused to measure species density and identify patterns of ecological change. By sampling in a manner robust against spurious mid‐domain effects, I aim to identify biologically valid controls on species density. Location The study area consists of land below 4250 m elevation between 27.1 and 27.8° N latitude, 86.5 and 88.0° E longitude on the southern slopes of the Himalaya Range in eastern Nepal. Sampling sites are limited to intact, natural forest with relatively little human impact. Methods Team members counted species of understorey plants and trees ≥ 10 cm d.b.h. in 0.04 ha plots throughout the study area. In addition, basal area, leafing phenology and species composition were determined for the trees in each plot. Estimates of regional species density were compiled for successive 250 m elevation bands from 250 to 4250 m elevation. Species density trends were identified and compared with the expectations of O'Brien's [Journal of Biogeography 25 (1998) 379–398] climate‐based water–energy dynamics model. Results Stand basal area, tree leafing phenology and taxonomic composition (angiosperm vs. gymnosperm) show non‐random change with elevation. Understorey plant and tree species density both have a humped, unimodal trend with more species near the bottom of the gradient and fewest at the top. These trends are consistent with expected effects of the climatically active water and energy variables. After curve‐fitting, significant spatial structure in the residuals suggests that tree communities within the 1750–2250 m elevation range do not realize their climatic potential species richness. Main conclusions Neither mid‐domain effects nor biologically valid boundary effects like dispersal limitation explain the plant species density trends observed. Trends do fit a model in which species density is controlled by the same ‘active’ climatic variables that predict species richness on continental scales. Patterns of leafing phenology on the elevation gradient provide further support for the hypothesis of environmental control of species density. The productivity–diversity linkage that exists on continental scales may also apply on the smaller scale of a Himalayan elevation gradient. Human activity and possible competitive exclusion by Castanopsis tribuloides are the two best explanations for the observed decline in tree species density at 1750–2250 m elevation. Burning, lopping for fodder and livestock grazing might account for the decline, but this study does not assess the relative importance of these activities. The elevation richest for understorey plant and tree species (500–1500 m) also has the most severe reduction in forest cover. Local farmers deserve credit for sustaining plant biodiversity in forest enclaves, but further loss of forest at these elevations should be discouraged.     

Variation in freshwater fish assemblages along a regional elevation gradient in the northern Andes,Colombia

Studies on elevation diversity gradients have covered a large number of taxa and regions throughout the world; however, studies of freshwater fish are scarce and restricted to examining their changes along a specific gradient. These studies have reported a monotonic decrease in species richness with increasing elevation, but ignore the high taxonomic differentiation of each headwater assemblage that may generate high β‐diversity among them. Here, we analyzed how fish assemblages vary with elevation among regional elevation bands, and how these changes are related to four environmental clines and to changes in the distribution, habitat use, and the morphology of fish species. Using a standardized field sampling technique, we assessed three different diversity and two structural assemblage measures across six regional elevation bands located in the northern Andes (Colombia). Each species was assigned to a functional group based on its body shape, habitat use, morphological, and/or behavioral adaptations. Additionally, at each sampling site, we measured four environmental variables. Our analyses showed: (1) After a monotonic decrease in species richness, we detected an increase in richness in the upper part of the gradient; (2) diversity patterns vary depending on the diversity measure used; (3) diversity patterns can be attributed to changes in species distribution and in the richness and proportions of functional groups along the regional elevation gradient; and (4) diversity patterns and changes in functional groups are highly correlated with variations in environmental variables, which also vary with elevation. These results suggest a novel pattern of variation in species richness with elevation: Species richness increases at the headwaters of the northern Andes owing to the cumulative number of endemic species there. This highlights the need for large‐scale studies and has important implications for the aquatic conservation of the region.