Effects of habitat fragmentation and disturbance on howler monkeys: a review

We examined the literature on the effects of habitat fragmentation and disturbance on howler monkeys (genus Alouatta) to (1) identify different threats that may affect howlers in fragmented landscapes; (2) review specific predictions developed in fragmentation theory and (3) identify the empirical evidence supporting these predictions. Although howlers are known for their ability to persist in both conserved and disturbed conditions, we found evidence that they are negatively affected by high levels of habitat loss, fragmentation and degradation. Patch size appears to be the main factor constraining populations in fragmented habitats, probably because patch size is positively related to food availability, and negatively related to anthropogenic pressures, physiological stress and parasite loads. Patch isolation is not a strong predictor of either patch occupancy or population size in howlers, a result that may be related to the ability of howlers to move among forest patches. Thus, we propose that it is probable that habitat loss has larger consistent negative effects on howler populations than habitat fragmentation per se. In general, food availability decreases with patch size, not only due to habitat loss, but also because the density of big trees, plant species richness and howlers' home range size are lower in smaller patches, where howlers' population densities are commonly higher. However, it is unclear which vegetation attributes have the biggest influence on howler populations. Similarly, our knowledge is still limited concerning the effects of postfragmentation threats (e.g. hunting and logging) on howlers living in forest patches, and how several endogenous threats (e.g. genetic diversity, physiological stress, and parasitism) affect the distribution, population structure and persistence of howlers. More long‐term studies with comparable methods are necessary to quantify some of the patterns discussed in this review, and determine through meta‐analyses whether there are significant inter‐specific differences in species' responses to habitat loss and fragmentation. Am. J. Primatol. 72:1–16, 2010. © 2009 Wiley‐Liss, Inc.     

Comparison of natural and artificial epidemics of take-all in sequences of winter wheat crops

Winter wheat was grown for six successive years (Expt 1) and for three successive years (Expt 2) in field experiments on different soil types. Artificial inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici cultured on autoclaved oat grains) was incorporated in the soil of some of the plots just before, or at, sowing of the first winter wheat crop. Expt 1 tested the incorporation of similar amounts of inoculum (212 kg ha^-1) at different depths. Expt 2 tested different amounts of inoculum at the same, shallow depth. Early sowing (September), late sowing (October) and spring inoculation were additional treatments, applied to the first crop only, in Expt 2. Seasonal factors apart, the disease outcome in the first year after inoculation depended on amounts and placement of applied inoculum, as well as date of sowing. Deeper inoculum resulted in less disease (Expt 1). Severe take-all was produced in Expt 2 by incorporating inoculum shallowly in sufficient quantities (400 kg ha^-1 or more). Less inoculum (200 kg ha^-1) generated less disease, especially in earlier-sown plots. Differences in disease amongst inoculum treatments were greatest in the first year and diminished subsequently, particularly where sowing had been early in the first year. In Expt 1, where first crops exposed to artificial inoculum developed moderate-to-severe disease, disease in subsequent second and/or third crops was less. In the fourth crop a second peak of disease occurred, coinciding with a first peak in sequences without added inoculum. Take-all decline (TAD) appeared to be expressed in all sequences thereafter. In Expt 2 in sequences without added inoculum, TAD occurred after a peak of disease in the second crop. Where 400 kg ha^-1 or more of inoculum were added, disease was severe in the first year and decreased progressively in successive years. Disease was less patchy in plots that received artificial inoculum. However, it remains uncertain mat severe disease caused by artificial inoculation achieved an early onset of true TAD. The infectivity of the top 12 cm of soil in the first 3 yr of Expt 1, determined by bioassay, depended on the depth of added inoculum and amount of disease in subsequent crops. However, at the time of the naturally occurring peak of disease severity (in either inoculated or non-inoculated plots) it did not predict either disease or TAD. Differences and similarities amongst epidemics developing naturally and those developing from different amounts and placement of applied inoculum have been revealed. The epidemiological implications of adding inoculum and the potential value of artificially-created epidemics of take-all in field trials are discussed.     

Biophysical stratification of the Amazon basin

In field measurement programmes, stratified sampling can optimize sampling efficiency, but stratification is often undertaken subjectively, and is frequently based on a priori classification schemes such as those used for vegetation maps. In order to avoid the problems associated with a priori subjective schemes, we explore here an objective procedure, Regression Tree Analysis (RTA). RTA has previously been used in local-scale studies, but here we apply it to a very large study domain, namely the entire humid tropical zone of South America. The aim of the study was to develop an optimal sampling design in preparation for the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). Co-registered spatially continuous fields of rainfall, temperature, photosynthetically active radiation (PAR), the normalized difference index (NDVI), an index of surface moisture, and other independent variables were used to predict three dependent variables, annual net radiation (Rn), latent heat (LE) and net primary production (NPP). Rather than simply dividing the study area based on differing levels of the three dependent variables, empirical models were developed using RTA to indicate how the relationships between these and possible forcing variables vary across the study area. For each variable long-term seasonal indices such as annual average, monthly minimum and amplitude were used to exclude effects of temporal phase differences between the hemispheres. The resulting hierarchical models revealed variations in the interdependence of the forcing variables throughout the study area and therefore provided a basis for a stratified sampling and identifying the most important variables to be collected in LBA for the Amazon basin as a whole as well as optimizing the sampling scheme for scaling up findings from the field scale to larger areas.     

Effects of nest-box density on the behavior of Tree Swallows during nest building

ABSTRACT.   In territorial species, increased density is often linked to an increase in aggressive interactions, which may result in trade-offs between competitive behavior and nest construction. We examined the impact of nesting in areas of high-density versus low-density nest boxes on conspecific interactions and nest-building effort in a population of Tree Swallows ( Tachycineta bicolor ). We also examined whether expected differences in behavior related to variation in nest quality and reproductive success in high-density and low-density areas. No differences in either nest-building behavior or reproductive success were observed between areas of high-density and low-density boxes, but there was a tendency of more frequent behavioral interactions at high density. Similarly, there was a significant difference between pairs defending single nest boxes and those defending multiple nest boxes in the number of interactions with conspecifics. These results suggest that although there may be more competition with conspecifics for Tree Swallows nesting at high density, this does not appear to affect either nest quality or reproductive success.     

Is microbial community composition in boreal forest soils determined by pH,C-to-N ratio,the trees,or all three?

In Fennoscandian boreal forests, soil pH and N supply generally increase downhill as a result of water transport of base cations and N, respectively. Simultaneously, forest productivity increases, the understory changes from ericaceous dwarf shrubs to tall herbs; in the soil, fungi decrease whereas bacteria increase. The composition of the soil microbial community is mainly thought to be controlled by the pH and C-to-N ratio of the substrate. However, the latter also determines the N supply to plants, the plant community composition, and should also affect plant allocation of C below ground to roots and a major functional group of microbes, mycorrhizal fungi. We used phospholipid fatty acids (PLFAs) to analyze the potential importance of mycorrhizal fungi by comparing the microbial community composition in a tree-girdling experiment, where tree belowground C allocation was terminated, and in a long-term (34 years) N loading experiment, with the shifts across a natural pH and N supply gradient. Both tree girdling and N loading caused a decline of ca. 45% of the fungal biomarker PLFA 18:2ω6,9, suggesting a common mechanism, i.e., that N loading caused a decrease in the C supply to ectomycorrhizal fungi just as tree girdling did. The total abundance of bacterial PLFAs did not respond to tree girdling or to N loading, in which cases the pH (of the mor layer) did not change appreciably, but bacterial PLFAs increased considerably when pH increased across the natural gradient. Fungal biomass was high only in acid soil (pH < 4.1) with a high C-to-N ratio (>38). According to a principal component analysis, the soil C-to-N ratio was as good as predictor of microbial community structure as pH. Our study thus indicated the soil C-to-N ratio, and the response of trees to this ratio, as important factors that together with soil pH influence soil microbial community composition.     

Inferring developmental constraint and constraint release: primordial germ cell determination mechanisms as examples

Developmental constraint and its converse constraint release are significant concepts in understanding pattern and process in macroevolution. The purpose of this paper is to propose a two-step method for identifying constraints and constraint release. The first step is a phylogenetic optimization procedure to identify which trait/process is primitive and which is derived. The primitive trait is inferred to be the constraint and the convergently derived trait the release. The second criterion uses sister-clade asymmetry. Clades diagnosed by the constraint will have fewer taxa than clades diagnosed by the release. As an example, we use the process of germ cell specification, in which there are three modes of specification. Our results corroborate previous conclusions that the induced mode is the constraint and the predetermined mode is the release and we speculate on the importance of these two processes in terms of robustness and evolvability.     

Food web structure and interaction strength pave the way for vulnerability to extinction

This paper focuses on how food web structure and interactions among species affects the vulnerability, due to environmental variability, to extinction of species at different positions in model food webs. Vulnerability is here not measured by a traditional extinction threshold but is instead inspired by the IUCN criteria for endangered species: an observed rapid decline in population abundance. Using model webs influenced by stochasticity with zero autocorrelation, we investigate the ecological determinants of species vulnerability, i.e. the trophic interactions between species and food web structure and how these interact with the risk of sudden drops in abundance of species. We find that (i) producers fulfil the criterion of vulnerable species more frequently than other species, (ii) food web structure is related to vulnerability, and (iii) the vulnerability of species is greater when involved in a strong trophic interaction than when not. We note that our result on the relationship between extinction risk and trophic position of species contradict previous suggestions and argue that the main reason for the discrepancy probably is due to the fact that we study the vulnerability to environmental stochasticity and not extinction risk due to overexploitation, habitat destruction or interactions with introduced species. Thus, we suggest that the vulnerability of species to environmental stochasticity may be differently related to trophic position than the vulnerability of species to other factors. Earlier research on species extinctions has looked for intrinsic traits of species that correlate with increased vulnerability to extinction. However, to fully understand the extinction process we must also consider that species interactions may affect vulnerability and that not all extinctions are the result of long, gradual reductions in species abundances. Under environmental stochasticity (which importance frequently is assumed to increase as a result of climate change) and direct and indirect interactions with other species some extinctions may occur rapidly and apparently unexpectedly. To identify the first declines of population abundances that may escalate and lead to extinctions as early as possible, we need to recognize which species are at greatest risk of entering such dangerous routes and under what circumstances. This new perspective may contribute to our understanding of the processes leading to extinction of populations and eventually species. This is especially urgent in the light of the current biodiversity crisis where a large fraction of the world's biodiversity is threatened.     

Effects of filamentous algal mats on sulfide invasion in eelgrass (Zostera marina)

The effect of filamentous algae invasion into Zostera marina meadows on water quality, sediment sulfur pools and sulfide invasion into plant tissues was studied experimentally. Sulfide invasion was assessed through analysis of sulfur isotopic composition (δ³⁴S) and total sulfur (TS) concentrations in plant tissues. The algal mats (5 and 10 cm thickness) depleted oxygen in the mats and increased the pools of sulfides in the sediments. Plants exposed to algal mats had δ³⁴S signals closer to the δ³⁴S of sediment sulfide, whereas plants with no mats present had δ³⁴S signals closer to the δ³⁴S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to algal mats. The δ³⁴S varied between the plant tissues with the leaves having more positive δ³⁴S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS concentrations were higher in plants exposed to algal mats suggesting that sulfur derived from sediment sulfide accumulated in the plants. F_sulfide showed that up to 50% of the sulfides in the plants were derived from sedimentary sulfides. The combined effect of water column anoxia in the lower parts of the meadow and high sulfide invasion into the plants lead to significantly reduced growth rates after 3 weeks and the below-ground tissues showed signs of degradation suggesting that algal mats invasion in to Zostera marina meadows can result in seagrass decline.     

Survival of Rio Grande Wild Turkeys on the Edwards Plateau of Texas

Abstract: The southeastern portion of the Edwards Plateau of Texas, historically a stronghold of Rio Grande wild turkeys (Meleagris gallopavo intermedia), has seen a decline in turkey numbers since the 1970s. Because adult and juvenile survival are key parameters affecting turkey population dynamics, we used radiotagged individuals to compare Rio Grande wild turkey survival in areas of suspected decline versus stable portions of the Edwards Plateau during 2001–2003. Reproductive period (breeding or nonbreeding) had an impact on survival, but differences in age, sex, or region did not influence survival. Model averaged estimates of monthly survival were 0.97 (SE = 0.005) for nonbreeding periods and 0.96 (SE = 0.007) for breeding periods. Our results indicate juvenile and adult survival in the declining areas was similar to survival in the stable areas of the Edwards Plateau. This suggests causes of the decline might be associated with differences during other life-history stages, such as nest success or poult survival, although we cannot rule out the possibility juvenile or adult survival contributed to the decline in the past. This situation demonstrates why wildlife managers should be cognizant of the implications of initiating long-term monitoring programs after changes in population status occur, rather than initiating them in expectation of such changes.     

Successive cambia development in Avicennia marina (Forssk.) Vierh. is not climatically driven in the seasonal climate at Gazi Bay, Kenya

This study is intended to provide early access to recent findings on the formation of the successive cambia of Avicennia marina (Forssk.) Vierh. in Kenya. The non-annual character of the growth layers was demonstrated by using three trees from a cambial marking experiment and three trees from a plantation of known age. The respective number of growth layers produced during one year was on average a half and three. Considering 28 stem disks of trees at three study sites, differing in local site conditions, growth layer development was shown to be strongly correlated with stem diameter (R²=0.84, p<0.0001, n=31). However, an additional influence of the site conditions was also demonstrated (homogeneity-of-slopes model test: F=54.72, p<0.0001, n=28). With increasing salinity and/or inundation class the width of the growth layers decreased. The significance of these variations in growth layer width offer interesting perspectives. The larger proportion of xylem in comparison with phloem in trees with wide as opposed to narrow growth layers may provide extra mechanical strength. On the other hand, the larger fraction of living tissue (phloem and parenchyma) in trees with thin growth layers may be beneficial for the water balance of the tree. Next to the non-annual nature of the growth layers and their networking pattern, more than one cambium was found to be simultaneously active. We conclude that classical dendrochronological methods (ring width measurements) should not be applied to A. marina (from Kenya).