Estimating the spatial scales of landscape effects on abundance

Context

Spatial variation in abundance is influenced by local- and landscape-level environmental variables, but modeling landscape effects is challenging because the spatial scales of the relationships are unknown. Current approaches involve buffering survey locations with polygons of various sizes and using model selection to identify the best scale. The buffering approach does not acknowledge that the influence of surrounding landscape features should diminish with distance, and it does not yield an estimate of the unknown scale parameters.

Objectives

The purpose of this paper is to present an approach that allows for statistical inference about the scales at which landscape variables affect abundance.

Methods

Our method uses smoothing kernels to average landscape variables around focal sites and uses maximum likelihood to estimate the scale parameters of the kernels and the effects of the smoothed variables on abundance. We assessed model performance using a simulation study and an avian point count dataset.

Results

The simulation study demonstrated that estimators are unbiased and produce correct confidence interval coverage except in the rare case in which there is little spatial autocorrelation in the landscape variable. Canada warbler abundance was more highly correlated with site-level measures of NDVI than landscape-level NDVI, but the reverse was true for elevation. Canada warbler abundance was highest when elevation in the surrounding landscape, defined by an estimated Gaussian kernel, was between 1300 and 1400 m.

Conclusions

Our method provides a rigorous way of formally estimating the scales at which landscape variables affect abundance, and it can be embedded within most classes of statistical models.

     

Feeding behavior under dark conditions in larvae of sutchi catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>

Sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature sensory organs; however, sensory organs develop rapidly with larval growth. Two-day-old larvae commenced ingesting Artemia nauplii. The larvae displayed many taste buds on the barbels, the head surface, and in the buccal cavity. Other sense organs were also well developed at this stage. Feeding experiments revealed that 2-day-old larvae ingested Artemia under both light and dark conditions, moreover, the larvae could ingest frozen dead Artemia. The ingestion rates for 4- and 7-day-old larvae were significantly higher under dark conditions than under light conditions. The rates using frozen dead Artemia were mostly higher than the rates using live Artemia. Therefore, feeding behavior under dark conditions is most likely not mediated by visual or mechanical senses, but rather by chemosensory senses, such as taste buds. Larval fish are vulnerable to predators; thus, if they can search for and eat food at night, they can avoid diurnal predators. The behavior observed here appears to represent their survival strategy. Moreover, these results suggest a new possibility that sutchi catfish larvae can be reared under dark or dim light conditions in order to improve survival and growth rates as in the case of African catfish Clarias gariepinus.     

A NMR study of water distribution in hardwoods at several equilibrium moisture contents

The water state of one tropical (Robinia coccinea) and two temperate (Acer saccharum and Fagus grandifolia) hardwoods was determined at different equilibrium moisture contents (EMC) during desorption at 25°C. NMR technique was used to separate different components of water in wood. The species studied presented different structures, which were apparent on the spin–spin relaxation T₂ values. Three different water components were separated: slow T₂ (liquid water in vessel elements), medium T₂ (liquid water in fiber and parenchyma elements) and fast T₂ (bound or cell wall water). The NMR results showed that even at equilibrated conditions a region exists where loss of liquid water and bound water takes place simultaneously. This region will vary according to the wood structure. Finally, liquid water was present at EMC lower than the fiber saturation point, which contradicts the concept of this point when considered as a bulk property of wood.     

Relating tradable credits for biodiversity to sustainability criteria in a dynamic landscape

Tradable biodiversity credit systems provide flexible means to resolve conflicts between development and conservation land-use options for habitats occupied by threatened or endangered species. We describe an approach to incorporate the influence of habitat fragmentation into the conservation value of tradable credits. Habitat fragmentation decreases gene flow, increases rates of genetic drift and inbreeding, and increases probabilities of patch extinction. Importantly, tradable credit systems will change the level of fragmentation over time for small and/or declining populations. We apply landscape equivalency analysis (LEA), a generalizable, landscape-scale accounting system that assigns conservation value to habitat patches based on patch contributions to abundance and genetic variance at landscape scales. By evaluating habitat trades using two models that vary the relationship between dispersal behaviors and landscape patterns, we show that LEA provides a novel method for limiting access to habitat at the landscape-scale, recognizing that the appropriate amount of migration needed to supplement patch recruitment and to offset drift and inbreeding will vary as landscape pattern changes over time. We also found that decisions based on probabilities of persistence alone would ignore changes in migration, genetic drift, and patch extinction that result from habitat trades. The general principle of LEA is that habitat patches traded should make at least equivalent contributions to rates of recruitment and migration estimated at a landscape scale. Traditional approaches for assessing the “take” and “jeopardy” standards under the Endangered Species Act based on changes in abundance and probability of persistence may be inadequate to prevent trades that increase fragmentation.     

Elevated carbon dioxide and temperature effects on rice yield,leaf greenness,and phenological stages duration

The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO₂]) (550 μmol mol^?1) and air temperature (+2–3 °C) on japonica rice (Oryza sativa L. “Ariete”) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO₂]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO₂] (average 382 μmol mol^?1). Results obtained showed that the rice “Ariete” had a moderate high yielding under open-field condition, but was susceptible to air temperature rise of +2–3 °C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO₂] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.     

Species proportions by area in mixtures of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species’ proportions estimated with this method are best approximated by the proportions of the species’ leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.     

Growth,P uptake and rhizosphere properties of wheat and canola genotypes in an alkaline soil with low P availability

The aim of the present study was to assess the role of soil type on growth, P uptake and rhizosphere properties of wheat and canola genotypes in an alkaline soil with low P availability. Two wheat (Goldmark and Janz) and two canola genotypes (Drum and Outback) were grown in a calcareous soil (pH 8.5) at two P levels [no P addition (0P) or addition of 200 mg kg⁻¹ P as Ca₃(PO₄)₂ (200P)] and harvested at flowering or maturity. Shoot and root dry weight, root length and shoot P content were greater in the two canola genotypes than in wheat. There were no consistent differences in available P, microbial P and phosphatase activity in the rhizosphere of the different genotypes. Shoot P content was significantly positively correlated with root length, pH and phosphatase activity in the rhizosphere. The microbial community composition, assessed by fatty acid methylester analysis, of the canola genotypes differed strongly from that of the wheat genotypes. The weight percentage bacterial fatty acids, the bacteria/fungi (b/f) ratio and the diversity of fatty acids were greater in the rhizosphere of the canolas than in the rhizosphere of the wheat genotypes. In contrast to the earlier studies in an acidic soil, only small differences in growth and P uptake between the genotypes of one crop were detected in the alkaline soil used here. The results confirmed the importance of root length for P uptake in soils with low P availability and suggest that the rhizosphere microbial community composition may play a role in the better growth of the canola compared to the wheat genotypes.     

Influence of clay content and acidity of soil on development of the earthworm <Emphasis Type="Italic">Lumbricus rubellus</Emphasis> and its population level consequences

In this paper we report on the influence of clay content and acidity of soil on growth and reproduction of the epigeic earthworm species Lumbricus rubellus (Hoffm.), which is common in most temperate soils and abundant in grasslands. Growth, cocoon production and survival of L. rubellus were tested in 12 Dutch soils which differed in soil properties. A matrix model was used to assess the population-level consequences of changes in growth and reproduction. Soil acidity had a strong negative effect on earthworm survival, and the maturation weight decreased with clay content. Individual weight gain in L. rubellus decreased with both acidity and clay content. The acidity of soils had a larger influence on population growth rate than the clay content. The acidity of the soil also changed the population composition towards younger age classes, whereas in soils rich in clay, the population composition did not change. The average individual weight of L. rubellus in clayey soils, however, was lower compared with that in soils low in clay, a result that agrees with literature data.     

Livelihood change,farming, and managing flood risk in the Lerma Valley,Mexico

In face of rising flood losses globally, the approach of “living with floods,” rather than relying on structural measures for flood control and prevention, is acquiring greater resonance in diverse socioeconomic contexts. In the Lerma Valley in the state of Mexico, rapid industrialization, population growth, and the declining value of agricultural products are driving livelihood and land use change, exposing increasing numbers of people to flooding. However, data collected in two case studies of farm communities affected by flooding in 2003 illustrate that the concept of flood as agricultural “hazard” has been relatively recently constructed through public intervention in river management and disaster compensation. While farming still represents subsistence value to rural households, increasingly rural communities are relying on non-farm income and alternative livelihood strategies. In this context, defining flooding in rural areas as a private hazard for which individuals are entitled to public protection may be counterproductive. A different approach, in which farmers’ long acceptance of periodic flooding is combined with valuing agricultural land for ecoservices, may enable a more sustainable future for the region’s population.

Evaluation of technologies for sequestering carbon in agricultural land by using organic filter underdrains

Technology for storing carbon in the subsoil of agricultural land using organic filter materials in underdrains was evaluated as an activity for sequestering CO₂ to mitigate global warming. First, the quantity of carbon remaining in wood chips and rice husks in underdrains was determined over 11 years after construction. Moreover, the quantity of CO₂ emissions from the construction of two underdrain types was calculated. Then, a survey was conducted to investigate the effect on greenhouse gas emissions of the filter material. The results indicate that greenhouse gas emissions would not increase. The quantity of storage carbon in the wood chip filter material of underdrains during their 15-year service life was estimated to be 6.76 tCO₂eq ha^?1. Rice husks, in contrast, were found ineffective in storing carbon. Therefore, the selection of the filter material for underdrains is important. The value of storage carbon in the wood chip filter material is similar to the amount of carbon sequestered by no-till farming, which is now being implemented as a global warming countermeasure based on soil management in agricultural land.