Relationships between species richness, evenness, and abundance in a southwestern savanna

Species richness and evenness are components of biological diversity that may or may not be correlated with one another and with patterns of species abundance. We compared these attributes among flowering plants, grasshoppers, butterflies, lizards, summer birds, winter birds, and rodents across 48 plots in the grasslands and mesquite-oak savannas of southeastern Arizona. Species richness and evenness were uncorrelated or weakly negatively correlated for each taxonomic group, supporting the conclusion that richness alone is an incomplete measure of diversity. In each case, richness was positively correlated with one or more measures of abundance. By contrast, evenness usually was negatively correlated with the abundance variables, reflecting the fact that plots with high evenness generally were those where all species present were about equally uncommon. Therefore richness, but not evenness, usually was a positive predictor of places of conservation value, if these are defined as places where species of interest are especially abundant. Species diversity was more positively correlated with evenness than with richness among grasshoppers and flowering plants, in contrast to the other taxonomic groups, and the positive correlations between richness and abundance were comparatively weak for grasshoppers and plants as well. Both of these differences can be attributed to the fact that assemblages of plants and grasshoppers were numerically dominated by small subsets of common species (grasses and certain spur-throated grasshoppers) whose abundances differed greatly among plots in ways unrelated to species richness of the groups as a whole.     

Cooperative breeding and immunity: a comparative study of PHA response in African birds

Cooperatively breeding birds might be expected to suffer from higher costs of parasitism than pair-breeding species because of two aspects of their ecology which should facilitate horizontal transmission and possibly select for higher parasite virulence: first, they interact regularly with more individuals than pair-breeding species, and second, these individuals are commonly close relatives that could share similar resistance alleles. This hypothesis predicts that cooperative breeders should invest relatively more in immune defence than closely related species which breed in pairs. I tested this prediction comparatively in African birds by examining the response of the immune system to the mitogenic lectin, phytoahemagglutinin (PHA response) in relation to cooperative breeding. Among 66 species, of which 18 breed cooperatively, PHA response was significantly higher in cooperatively breeding species. This association appeared not to be confounded by body size, clutch size, nest position, coloniality or similarity owing to common phylogenetic descent. These results suggest that cooperatively breeding birds may have been selected to invest more than pair-breeders in defences against parasites. If so, then additional costs of philopatry and helping behaviour might be imposed on breeders, helpers and offspring.     

Effects of climate and exurban development on nest predation and predator presence in the southern Appalachian Mountains (USA)

In the eastern United States, land-use and climate change have likely contributed to declines in the abundance of Neotropical migrant birds that occupy forest interiors, but the mechanisms are not well understood. We conducted a nest-predation experiment in southern Appalachian Mountain forests (North Carolina, U.S.A.) during the 2009 and 2010 breeding seasons to determine the effects of exurban development and temperature on predator presence and the average number of days until eggs in an artificial nest were disturbed by predators. We baited artificial nests with quail (Excalfactoria chinensi) eggs and monitored them for 18 days. We used clay eggs, track plates, and motion-triggered cameras to detect and identify nest predators. The average number of days a nest was undisturbed decreased as mean temperature increased and, to a lesser extent, as the density of buildings increased. Nests on the ground were more often depredated than those in trees, likely due to increased predation by opossum (Didelphis virginiana) and other carnivores. Raccoons (Procyon lotor), opossums, corvids (Corvus brachyrhynchos and Cyanocitta cristata), chipmunks (Tamias striatus), black bears (Ursus americanus), and domestic cats (Felis catus) were the most commonly detected predators. Presence of these predators did not vary as a function of mean temperature. Domestic cats and corvids were detected more frequently in plots with high rather than low densities of buildings. Forest-interior specialists and Neotropical migrants often nest in cool, high-elevation areas with low housing density. These bird species, especially those that nest on the ground, may be most vulnerable to increased nest predation if temperature and exurban development increase at higher elevations as anticipated.     

Postfire stand structure in a semiarid savanna: cross-scale challenges estimating biomass.

Algorithms relating remotely sensed woody cover to biomass are often the basis for large-scale inventories of aboveground carbon stocks. However, these algorithms are commonly applied in a generic fashion without consideration of disturbances that might alter vegetation structure. We compared field and remote sensing estimates of woody biomass on savannas with contrasting disturbance (fire) histories and assessed potential errors in estimating woody biomass from cover without considering fire history. Field surveys quantified multilayer cover (MLC) of woody and succulent plants on sites experiencing wildfire in 1989 or 1994 and on nearby unburned (control) sites. Remote sensing estimates of the woody cover fraction (WCF) on burned and control sites were derived from contemporary (2005) dry-season Landsat Thematic Mapper imagery (during a period when herbaceous cover was senescent) using a probabilistic spectral mixture analysis model. Satellite WCF estimates were compared to field MLC assessments and related to aboveground biomass using allometry. Field-based MLC and remotely sensed WCFs both indicated that woody cover was comparable on control areas and areas burned 11-16 years ago. However, biomass was approximately twofold higher on control sites. Canopy cover was a strong predictor of woody biomass on burned and control areas, but fire history significantly altered the linear cover-biomass relationship on control plots to a curvilinear relationship on burned plots. Results suggest predictions of woody biomass from "generic" two-dimensional (2-D) cover algorithms may underestimate biomass in undisturbed stands and overestimate biomass in stands recovering from disturbance. Improving the accuracy of woody-biomass estimates from field and/or remotely sensed cover may therefore require disturbance-specific models or detection of vegetation height and transforming 2-D vegetation cover to 3-D vegetation volume.     

Environmental change and vulnerability in the Usangu plain,southwestern Tanzania: Implications for sustainable development

Natural resources are important assets for sustainability of rural livelihoods and economic development. The objectives of the study were to assess linkage of environmental change to emerging water scarcity, livelihoods insecurity and decline in wildlife biodiversity and hydropower generation in the Great Ruaha ecosystem, and to discuss policy lessons for sustainable development. Literature survey, participatory assessments, collection of records from stakeholders, participatory observations and a questionnaire survey were used. Participatory assessment found that increasing water scarcity is associated with degradation of land, vegetation cover and change in rainfall intensity and duration. Rainfall change is supported by 83% of respondents and rainfall trends analysis. About 42% of variation in cereal production is described by the rainfall amount variability. Analysis of trends for per capita cereals production from district records showed a significant (p < 0.05) decline over the years. Changes in water flows in the Great Ruaha River have been evident since 1993, and have affected wildlife diversity in the Ruaha National Park and power generation from the Kidatu hydroelectric plant downstream. Human livelihood activities, exclusiveness, weak coordination and collaboration between sectors and institutions in policy formulation and implementation have played a role. The pro-poor policy formulation through integrated planning, strong coordination and collaboration is recommended for sustainable development.     

Eumelanin-based coloration and fitness parameters in birds: a meta-analysis

Although melanin is the most common pigment in animal integuments, the adaptive function of variation in melanin-based coloration remains poorly understood. The individual fitness returns associated with melanin pigments can be variable across species as these pigments can have physical and biological protective properties and genes involved in melanogenesis may vary in the intensity of pleiotropic effects. Moreover, dark and pale coloration can also enhance camouflage in alternative habitats and melanin-based coloration can be involved in social interactions. We investigated whether darker or paler individuals achieve a higher fitness in birds, a taxon wherein associations between melanin-based coloration and fitness parameters have been studied in a large number of species. A meta-analysis showed that the degree of melanin-based coloration was not significantly associated with laying date, clutch size, brood size, and survival across 26 species. Similar results were found when restricting the analyses to non-sexually dimorphic birds, colour polymorphic and monomorphic species, in passerines and non-passerines and in species for which inter-individual variation in melanism is due to colour intensity. However, eumelanic coloration was positively associated with clutch and brood size in sexually dimorphic species and those that vary in the size of black patches, respectively. Given that greater extent of melanin-based coloration was positively associated with reproductive parameters and survival in some species but negatively in other species, we conclude that in birds the sign and magnitude of selection exerted on melanin-based coloration is species- or trait-specific.     

The effect of non-uniform depth on the baroclinic response to wind in elongated basins

We examined the effect of along-thalweg depth variability on the baroclinic response to wind in elongated narrow basins with a sharp thermocline. The effect of depth variability was examined by deriving a modal-based forced model with two density layers and applying the model to a symmetric curved-bottom basin (CB), an asymmetric wedge-shaped basin (with a sloping bottom towards a vertical wall, WB), and a flat-bottom basin (FB). The baroclinic responses of CB, WB, and FB to uniform wind were found to differ in time-scale, number and energy of excited modes, and temporal pattern and along-thalweg structure of baroclinic flow and thermocline deflection. For all bottom profiles that were examined, the fundamental mode was found to dominate the response to spatially-uniform wind. Compared to FB, the asymmetric depth variability in WB increased the number and energy of excited higher modes and localized the interface shear, while the symmetric deviation from flat bottom in CB caused the opposite effects. Linear deviation from uniform wind was found to feed energy into higher baroclinic modes for the symmetric CB, but was found to reduce the energy of higher baroclinic modes for WB when the deviation from uniform wind is comparable to the spatial-average magnitude. Our results can explain the observation of the second baroclinic mode and irregular wave patterns in some lakes and reservoirs. Further, our results suggest that one-dimensional vertical mixed-layer models provide better results for shear entrainment in curved-bottom basins than in wedge-shaped basins.     

Density and extra-pair fertilizations in birds: a comparative analysis

Møller and Birkhead (1992, 1993) reported that extra-pair copulations (EPCs) occur more frequently in colonial than dispersed nesting birds. We comprehensively reviewed published data to investigate how breeding density affects extra-pair fertilizations (EPFs). Within species EPFs appeared to increase with density: two of three studies on colonial breeders and six of eight on dispersed nesters showed increases in EPFs with increasing density. However, comparisons among species (n?=?72) revealed no evidence that EPF frequencies correlated with (1) nesting dispersion, (2) local breeding density, or (3) breeding synchrony, even when each of these variables in turn was held constant and phylogenetic relationships were taken into account via contrast analyses. Methodological and biological reasons for the disparity between observational studies of EPCs and molecular genetic analyses of EPFs are discussed.     

Seed germination in response to chemicals: effect of nitrogen and pH in the media

Seed germination generally presents a peak in the next growing season after a fire. Among other factors associated with fire are the increase of soil nitrogen and changes in the pH of the soil. In this study, we addressed the question, whether or not the germination response of eight species is linked with the increase in pH and nitrogenous compounds in the germination media? We assessed the separate and combined effects of nitrogenous compounds and pH on the percentage and rate of germination of seeds of Medicago arabica (L.) Hudson, Epilobium hirsutum L., Foeniculum vulgare Miller, Daucus carota L., Thapsia villosa L., Cynosurus cristatus L., Dactylis glomerata L. and Rumex crispus L. All these species are well represented in the Mediterranean ecosystems of the central-west Spain. Water and CaCl2 were used as controls. Nitrogenous compounds increased percent germination (level) and rate in three of the species studied. High pH negatively affected the germination rate of seeds from most species, but had no effect on the per cent germination of any of the species. The higher concentration of the nutritious solutions affected negatively the germination level and rate. The different germination responses of seeds of the studied species could not be exclusively attributed to pH values in the media, whereas the amount and form of Nitrogen in the media has a greater effect on it. These differences in germination are species dependent.     

Inspection of mob-calls as sources of predator information: response of migrant and resident birds in the Neotropics

Migrating animals face numerous mortality risks, such as novel predators with which they may not be accustomed. Most animals can recognize predators innately; however, additional predator information can be collected to enhance familiarity. Because migrating birds rarely participate in mobs, they may seek alternative information sources such as cues provided by other birds that can provide information on predator location, identity, and degree of threat. We predicted that Nearctic–Neotropical migrants (hereafter, “migrants”) would react to vocal antipredator cues (e.g., mob-calls) of species residing in areas through which they migrate. To test this, we conducted experiments in Belize during spring migration, using playbacks of mob-calls of black-capped chickadees (Poecile atricapillus) and blue-gray tanagers (Thraupis episcopus); tanagers are familiar to all birds in Belize; chickadees are novel to residents but familiar to migrants. This also allowed us to assess response to novel and out-of-context antipredator signals. Resident birds did not respond to novel chickadee mob-calls, but did respond to familiar tanager calls. Birds overwintering south of our study area, which were migrating during our study, responded most strongly to chickadee playbacks. Conversely, individuals of species that include our study area in their winter range did not respond to either playback. This is the first evidence that birds react to vocal antipredator cues during migration, which may be a strategy used by migrants to learn about predators. Although residents failed to recognize a foreign cue, migrating birds responded most strongly to the out-of-context chickadee cue, associated with breeding grounds >2,000 km northward. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Avifaunal responses to fire in southwestern montane forests along a burn severity gradient.

The effects of burn severity on avian communities are poorly understood, yet this information is crucial to fire management programs. To quantify avian response patterns along a burn severity gradient, we sampled 49 random plots (2001-2002) at the 17351-ha Cerro Grande Fire (2000) in New Mexico, USA. Additionally, pre-fire avian surveys (1986-1988, 1990) created a unique opportunity to quantify avifaunal changes in 13 pre-fire transects (resampled in 2002) and to compare two designs for analyzing the effects of unplanned disturbances: after-only analysis and before-after comparisons. Distance analysis was used to calculate densities. We analyzed after-only densities for 21 species using gradient analysis, which detected a broad range of responses to increasing burn severity: (I) large significant declines, (II) weak, but significant declines, (III) no significant density changes, (IV) peak densities in low- or moderate-severity patches, (V) weak, but significant increases, and (VI) large significant increases. Overall, 71% of the species included in the after-only gradient analysis exhibited either positive or neutral density responses to fire effects across all or portions of the severity gradient (responses III-VI). We used pre/post pairs analysis to quantify density changes for 15 species using before-after comparisons; spatiotemporal variation in densities was large and confounded fire effects for most species. Only four species demonstrated significant effects of burn severity, and their densities were all higher in burned compared to unburned forests. Pre- and post-fire community similarity was high except in high-severity areas. Species richness was similar pre- and post-fire across all burn severities. Thus, ecosystem restoration programs based on the assumption that recent severe fires in Southwestern ponderosa pine forests have overriding negative ecological effects are not supported by our study of post-fire avian communities. This study illustrates the importance of quantifying burn severity and controlling confounding sources of spatiotemporal variation in studies of fire effects. After-only gradient analysis can be an efficient tool for quantifying fire effects. This analysis can also augment historical data sets that have small samples sizes coupled with high non-process variation, which limits the power of before-after comparisons.     

The role of the rural settlements in the Brazilian savanna deforesting process

Although the drivers of deforestation in Brazil are relatively well known, there is still limited understanding of the role of family farm-based rural settlements in land cover changes, particularly in the Brazilian savanna. This research aims to identify land use patterns within rural settlements and examine how they are influenced by regional dynamics. The study is based on GIS techniques and satellite image classification (Landsat 5-TM and RapidEye imagery), combined with geo-referenced fieldwork data in three different regions of the State of Goiás. The results reveal that the deforestation arrangement within the studied rural settlements is very similar to the deforestation found in the surrounding regions. As a positive outcome, the rural settlements have a higher share of remnant vegetation when compared to the surrounding areas, but this is still concentrated within legal reserves. We conclude that the changing patterns of rural settlement land cover are highly influenced by regional dynamics.     

Malaria and risk of predation: a comparative study of birds

Predators have been hypothesized to prey on individuals in a poor state of health, although this hypothesis has only rarely been examined. We used extensive data on prey abundance and availability from two long-term studies of the European Sparrowhawk (Accipiter nisus) and the Eurasian Goshawk (Accipiter gentilis) to quantify the relationship between predation risk of different prey species and infection with malaria and other protozoan blood parasites. Using a total of 31 745 prey individuals of 65 species of birds from 1709 nests during 1977-1997 for the Sparrowhawk and a total of 21 818 prey individuals of 76 species of birds from 1480 nests for the Goshawk during 1977-2004, we show that prey species with a high prevalence of blood parasites had higher risks of predation than species with a low prevalence. That was also the case when a number of confounding variables of prey species, such as body mass, breeding sociality, sexual dichromatism, and similarity among species in risk of predation due to common descent, were controlled in comparative analyses of standardized linear contrasts. Prevalence of the genera Haemoproteus, Leucocytozoon, Plasmodium, and Trypanosoma were correlated with each other, and we partitioned out the independent effects of different protozoan genera on predation risk in comparative analyses. Prevalence of Haemoproteus, Leucocytozoon, and Plasmodium accounted for interspecific variation in predation risk for the two raptors. These findings suggest that predation is an important factor affecting parasite-host dynamics because predators tend to prey on hosts that are more likely to be infected, thereby reducing the transmission success of parasites. Furthermore, this study demonstrates that protozoan infections are a common cause of death for hosts mediated by increased risk of predation.     

The air speed of migrating birds and its relationship to the wind

Summary This paper deals with the flight speeds of migrating birds observed by radar over a Swiss Alpine pass. The distributions of air speeds for different classes of birds and the influence of the wind on air speeds were investigated. Our findings differ greatly from observations of bird migration over the North Atlantic Ocean and the North American continent. Our data reveal: (1) that the air speeds of the bulk of migrating birds were in the range of 8–18 m/s and that the amount of slow flyers (air speed below 5 m/s) was less than 5%; (2) that there was an obvious influence of the wind on air speeds and, moreover, the data showed a distinctly variable compensatory behavior among different bird classes; (3) that the wind component in the direction of the bird's heading was a better predictor for air speed than the wind direction. Although we do not speculate about possibilities and mechanisms of wind detection, a simple argument shows how birds could estimate wind directions if they do use the moving surface as a reference system.     

荞麦叶内抗氧化系统对铝胁迫的响应

以荞麦(FagopyrumesculentumMoench)为实验材料,采用沙培法,研究了荞麦对不同铝质量浓度胁迫下体内保护酶的响应和变化规律。结果表明,铝胁迫下荞麦体内铝质量浓度的升高促进了过氧化物酶的活性,抑制了过氧化氢酶和超氧化物歧化酶的活性,增加了蛋白质、丙二醛、抗坏血酸和游离脯氨酸的含量;多酚氧化酶和抗坏血酸过氧化物酶在适当的铝质量浓度处理下活性都有提高。在高铝处理下,叶片中积累的铝明显较根和茎多。在铝的胁迫下,荞麦体内非酶系也发挥了重要的作用。     

The functional response of a hoarding seed predator to mast seeding

Mast seeding involves the episodic and synchronous production of large seed crops by perennial plants. The predator satiation hypothesis proposes that mast seeding maximizes seed escape because seed predators consume a decreasing proportion of available seeds with increasing seed production. However, the seed escape benefits of masting depend not only on whether predators are satiated at high levels of seed production, but also on the shape of their functional response (type II vs. type III), and the actual proportion of available seeds that they consume at different levels of seed production. North American red squirrels (Tamiasciurus hudsonicus) are the primary vertebrate predator of white spruce (Picea glauca) mast seed crops in many boreal regions because they hoard unopened cones in underground locations, preempting the normal sequence of cone opening, seed dispersal, and seed germination. We document the functional response of cone-hoarding by red squirrels across three non-mast years and one mast year by estimating the number of cones present in the territories of individual red squirrels and the proportion of these cones that they hoarded each autumn. Even though red squirrels are not constrained by the ingestive and on-body (fat reserves) energy reserve limitations experienced by animals that consume seeds directly, most squirrels hoarded < 10% of the cones present on their territories under mast conditions. Cone availability during non-mast years also reached levels that satiated the hoarding activity of red squirrels; however, this occurred only on the highest-quality territories. Squirrels switched to mushroom-hoarding when cone production was low and mushrooms were abundant. This resulted in type III functional response whereby the proportional harvest of cones was highest at levels of cone availability that were intermediate within non-mast years. Overall, more cones escaped squirrel cone-hoarding during a mast event than when cone production was low in non-mast years, which supports the predator satiation hypothesis. However, the highly variable seed escape in non-mast years may help to explain why all spruce cone production is not concentrated into fewer, larger, mast years.     

Mechanisms of sperm competition in birds: mathematical models

Summary We built models of sperm competition and compared their predictions with observations from domestic chickens in an attempt to elucidate the mechanism of sperm competition. The models suggest that (1) observed levels of precedence of sperm are not merely a passive consequence of the greater mortality of sperm from earlier inseminations; (2) displacement of existing sperm from sperm storage tubules by incoming sperm explains observed levels of sperm precedence and disappearance from the reproductive tract, even in the absence of recognition of sperm from different inseminations; (3) stratification of sperm within the sperm storage tubules fails as an explanation of observed patterns of sperm precedence and disappearance because long-term levels of sperm precedence as high as those observed can only be predicted in combination with rates of disappearance of sperm much lower than those observed in chickens. The predictions of sperm precedence levels following multiple inseminations also suggest that displacement rather than stratification is the most likely mechanism of sperm competition in chickens. We discuss the consequences of male or female control of sperm competition, non-uniform distribution of sperm between sperm storage tubules, and variation in sperm precedence with time after the last insemination, and suggest ways in which the models may be used in future to aid in the elucidation of mechanisms of sperm competition. Offprint requests to: C.M. Lessells