Why elephant have trunks and giraffe long tongues: how plants shape large herbivore mouth morphology

We investigated whether mass and morphological spatial patterns in plants possibly induced the development of enlarged soft mouth parts in especially megaherbivores. We used power functions and geometric principles to explore allometric relationships of both morphological and foraging characteristics of mammalian herbivores in the South African savannah, covering a body size range of more than three orders magnitude. Our results show that, although intradental mouth volume scaled to a power slightly less than one to body mass, actual bite volume, as measured in the field, scaled to body mass with a factor closer to 1.75. However, when including the volume added to intradental mouth volume by soft mouth parts, such as tongue and lips (or trunks in elephant), mouth volume scaled linearly with actual bite volume and in a similar fashion as actual bite volume to body size. Bite mass and bite leaf mass scaled linearly with body size. We conclude that these scaling relationships indicate that large herbivores use their enlarged soft mouth parts to not only increase bite volume and thereby bite mass, but also select soft plant parts and thereby increase the leaf mass fraction per bite.     

Carbon isotopes as indicators of elephant diets and African environments

Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used ¹³C/¹²C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ¹³C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C₃ plants) and graze (C₄ plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments.     

徐州市城区公园绿地土壤养分状况

以徐州市三环路内4个城区的公园绿地土壤为研究对象,通过对其土壤的养分状况及化学性质取样分析,结果表明有机质含量为(1.05±0.41)%、全氮含量(0.071±0.045)%、全磷含量(0.053±0.051)%、全钾含量(1.860±1.449)%、碱解氮(47.7±29.9)mg·kg^-1、速效磷(3.5±0.9)mg·kg^-1、速效钾(121.7±53.5)mg·kg^-1、PH值(8.31±1.55)。有机质及全量养分低于该地区自然褐土的平均值,有效养分不均衡,PH值有升高的趋势;有机质与全氮、全氮与碱解氮、PH值与速效钾有一定的相关性,其它指标间的相关性较差。     

The nutrient status of epiphytes and their host trees along an elevational gradient in Costa Rica

Vascular epiphytes are a conspicuous and highly diverse group in tropical wet forests; yet, we understand little about their mineral nutrition across sites. In this study, we examined the mineral nutrition of three dominant vascular epiphyte groups: ferns, orchids, and bromeliads, and their host trees from samples collected along a 2600 m elevational gradient in the tropical wet forests of Costa Rica. We predicted that the mineral nutrition of ferns, orchids, and bromeliads would differ because of their putative differences in nutrient acquisition mechanisms and nutrient sources—atmospherically dependent, foliar feeding bromeliads would have lower nitrogen (N) and phosphorous (P) concentrations and more depleted δ¹⁵N values than those in canopy soil-rooted ferns because canopy soil is higher in available N, and more enriched in δ¹⁵N than the atmospheric sources of precipitation and throughfall. We also predicted that epiphyte foliar chemistry would mirror that of host trees because of the likely contribution of host trees to the nutrient cycle of epiphytes via foliar leaching and litter contributions to canopy soil. In the same vein, we predicted that epiphyte and host tree foliar chemistry would vary with elevation reflecting ecosystem-level nutrients—soil N availability increases and P availability decreases with increasing elevation. Our results confirmed that canopy soil-rooted epiphytes had higher N concentrations than atmospheric epiphytes; however, our predictions were not confirmed with respect to P which did not vary among groups indicating fixed P availability within sites. In addition, foliar δ¹⁵N values did not match our prediction in that canopy soil-rooted as well as atmospheric epiphytes had variable signatures. Discriminant function analysis (DFA) on foliar measurements determined that ferns, orchids, and bromeliads are statistically distinct in mineral nutrition. We also found that P concentrations of ferns and orchids, but not bromeliads, were significantly correlated with those of host trees indicating a possible link in their mineral nutrition’s via canopy soil. Interestingly, we did not find any patterns of epiphyte foliar chemistry with elevation. These data indicate that the mineral nutrition of the studied epiphyte groups are distinct and highly variable within sites and the diverse uptake mechanisms of these epiphyte groups enhance resource partitioning which may be a mechanism for species richness maintenance in tropical forest canopies.     

Soil organic C and nutrient contents under trees with different functional characteristics in seasonally dry tropical silvopastures

Aims

The selection of tree characteristics is critical for the outcome of the tree effects on soil fertility in silvopastoral pastures. This study aims to quantify the effects of trees on soil nutrient and C stocks, as well as assessing differences on the effects between legume (Albizia saman; Enterolobium cyclocarpum) and non-legume tree species (Tabebuia rosea; Guazuma ulmifolia).

Methods

In Central Nicaragua, soil was sampled (0–10 cm deep) in paired plots, under both a canopy and in open grassland, in 12 sites per tree species and analysed for organic C, total N stocks, available P and extractable K⁺, Ca²⁺ and Mg²⁺. To assess the effects of herbaceous composition and cattle to soil proprieties, we recorded the cover of plant groups and assessed the mass of dung in each plot.

Results

Soil organic C and N, available P and extractable K⁺ and Ca²⁺ were higher under the tree canopy than under paired open grassland. The basal area of trees was positively related with the canopy effect on soil variables, thus suggesting that the age or sizes of the trees are relevant factors associated with the content of soil C and nutrients. No specific effects related to the legume species group were detected.

Conclusions

Our results indicate that in fertile seasonally dry subtropical pastures, scattered trees have an overall effect on soil fertility, and that the magnitude of the effect depends more on the tree characteristics (i.e. basal area, crown area) than on whether the species is a legume or not.     

洞庭湖西岸区防护林土壤和植物营养元素含量特征

对洞庭湖西岸区4种防护林地土壤与植物中营养元素含量进行研究。结果表明:环湖低丘平原封山育林和补植封山育林的水土保持林、平原湖区防护林pH值为4.54—5.27,呈酸性反应;防浪护堤林pH值为8.18,呈碱性反应。有机质和全N含量以环湖低丘平原封山育林的水土保持林地高于其余3种防护林,N素和P素有效率均低,速效N仅占全N含量的1.46%—3.35%,速效P仅占全P的0.5%—1.6%,全K含量亦不高,除环湖低丘平原封山育林的水土保持林地含K量适量外,其余3种防护林地均为严重缺K型土壤,防浪护堤林地全Ca及Mg含量高于其余3种防护林地。各防护林群落中植物体内不同营养元素含量差异很大,同一元素在不同植物体内含量的变化范围亦很大,高低值达几倍到十几倍,甚至几十倍。植物对土壤中营养元素的积累能力分为最强、中等和最弱3个层次。研究结果可为防护林体系建设和土壤肥力评价提供科学依据。     

白桦和落叶松苗木对其纯林土壤养分的生物检测

利用35年生白桦、落叶松纯林土壤分别栽植白桦、落叶松1年生苗木,通过对苗木生长、生物量、叶片养分及土壤养分变化的研究,对两种土壤的肥力进行评价,探讨白桦、落叶松混交林种间互作机制.结果表明:白桦纯林土壤全氮、碱解氮含量显著高于落叶松纯林土壤(P<0.05),落叶松纯林土壤全磷、全钾、速效磷含量显著高于白桦纯林土壤(P<0.05).盆栽第1年,白桦纯林土壤上的白桦苗木苗高、地径和生物量分别比在落叶松纯林土壤上增加69%、52%和65%(P<0.05),落叶松苗木分别增加12%、8%和37%(P>0.05).以白桦纯林土壤为基质时,白桦、落叶松苗木叶片氮浓度高于落叶松纯林土壤,而磷浓度低于落叶松纯林土壤.白桦凋落量大且分解速度快,落叶松对土壤磷具有活化作用,导致白桦纯林土壤氮素有效性较高,落叶松纯林土壤有效磷含量较高.推测两树种混交时,土壤氮、磷的互补作用可能对林分产量产生有益的作用.     

Background level of risk determines how prey categorize predators and non-predators

Much of the plasticity that prey exhibit in response to predators is linked to the prey''s immediate background level of risk. However, we know almost nothing of how background risk influences how prey learn to categorize predators and non-predators. Learning non-predators probably represents one of the most underappreciated aspects of anti-predator decision-making. Here, we provide larval damselfish (Pomacentrus chrysurus) with a high or low background risk and then try to teach them to recognize a cue as non-threatening through the process of latent inhibition. Prey from the low-risk background that were pre-exposed to the novel odour cues in the absence of negative reinforcement for 3 days, and then provided the opportunity to learn to recognize the odour as threatening, failed to subsequently respond to the odour as a threat. Fish from the high-risk background showed a much different response. These fish did not learn the odour as non-threatening, probably because the cost of falsely learning an odour as non-threatening is higher when the background level of risk is higher. Our work highlights that background level of risk appears to drive plasticity in cognition of prey animals learning to discriminate threats in their environment.     

Viewing geometry determines how vision and haptics combine in size perception

Vision and haptics have different limitations and advantages because they obtain information by different methods. If the brain combined information from the two senses optimally, it would rely more on the one providing more precise information for the current task. In this study, human observers judged the distance between two parallel surfaces in two within-modality experiments (vision-alone and haptics-alone) and in an intermodality experiment (vision and haptics together). In the within-modality experiments, the precision of visual estimates varied with surface orientation, as expected from geometric considerations; the precision of haptic estimates did not. An ideal observer that combines visual and haptic information weights them differently as a function of orientation. In the intermodality experiment, humans adjusted visual and haptic weights in a fashion quite similar to that of the ideal observer. As a result, combined size estimates are finer than is possible with either vision or haptics alone; indeed, they approach statistical optimality.     

Farmer preferences and legume intensification for low nutrient environments

Improved varieties of legumes adapted to nutrient deficiency have the potential to improve food security for the poorest farmers. Tolerant varieties could be an inexpensive and biologically smart technology that improves soils while minimizing fertilizer costs. Yet other technologies that improve productivity and appear to be biologically sound have been rejected by farmers. To translate benefits to smallholder farmers, research on low-nutrient tolerant genes and crop improvement must keep farmer preferences and belief systems in the forefront. We review farmer participatory research on legume-intensification and soil fertility management options for smallholder farmers in Africa, including recent results from our work in Malawi and Kenya. We suggest that indeterminate, long-duration legumes are the best bet for producing high quality residues, compared to short-duration and determinate genotypes. This may be due to a long period of time to biologically fix nitrogen, acquire nutrients, photosynthesize and grain fill. Also, the indeterminate nature of long-duration varieties facilitates recovery from intermittent stresses such as drought or pest pressure. However, indeterminate growth habit is also associated with late maturity, moderate yield potential and high labour demand. These traits are not necessarily compatible with smallholder criteria for acceptable varieties. Malawi women farmers, for example, prioritized early maturity and low-labour requirement, as well as yield potential. To address complex farmer requirements, we suggest the purposeful combination of species with different growth habits; e.g. deep-rooted indeterminate long-duration pigeonpea interplanted with short-duration soyabean and groudnut varieties. On-farm trials in Malawi indicate that calorie production can be increased by 30% through pigeonpea-intensified systems. Farmers consistently indicate strong interest in these systems. In Kenya, a 55% yield increase was observed for a doubled-up pigeonpea system (a double row of pigeonpea intercropped with three maize rows) compared to traditional, low density intercrops. However, the need for improved pigeonpea varieties with high intercrop suitability, including reduced early branching, was highlighted by a farmer preference study in the same area. These examples illustrate the potential for participatory research methodologies to drive biophysical research in farmer-acceptable directions.     

Above-ground space sequestration determines competitive success in juvenile beech and spruce trees

A 2-yr phytotron study was conducted to investigate the intra- and inter-specific competitive behaviour of juvenile beech (Fagus sylvatica) and spruce (Picea abies). Competitiveness was analysed by quantifying the resource budgets that occur along structures and within occupied space of relevance for competitive interaction. Ambient and elevated CO(2) and ozone (O(3)) regimes were applied throughout two growing seasons as stressors for provoking changes in resource budgets, growth and allocation to facilitate the competition analysis. The hypothesis tested was that the ability to sequester space at low structural cost will determine the competitive success. Spruce was a stronger competitor than beech, as displayed by its higher above-ground biomass increments in mixed culture compared with monoculture. A crucial factor in the competitive success of spruce was its ability to enlarge crown volume at low structural costs, supporting the hypothesis. Interspecific competition with spruce resulted in a size-independent readjustment of above-ground allocation in beech (reduced leaf : shoot biomass ratio). The efficient use of resources for above-ground space sequestration proved to be a parameter that quantitatively reflects competitiveness.     

Alternate bearing influences annual nutrient consumption and the total nutrient content of mature pistachio trees

The influence of alternate bearing on nutrient utilization and total tree nutrient content was investigated in mature pistachio (Pistacia vera L. cv Kerman trees). Removal of N, P and Zn in fruit and abscised leaves of cropping (‘on’) trees averaged 5, 6, and 2 times, respectively, the removal in abscised leaflets of the non-fruiting, ‘off’ year trees. One hundred and thirty-five kg N, 131 kg K, 86 kg Ca, 39 kg Mg and 18 kg P per hectare were removed in fruits and abscised leaves in ‘on’ year trees. Tree nutrient contents and, presumably, the size of nutrient storage pools in dormant trees varied between ‘on’ and ‘off’ years. There was 22% and 14% more N and P, respectively, in dormant trees following ‘off’ than ‘on’ years. The greater N and P accumulation in ‘off’ year trees is depleted in support of the large fruit demand for N and P during ‘on’ years. In contrast to N and P, there was greater K and Ca accumulation in perennial tree parts during ‘on’ years than during ‘off’ years. The greater K accumulation in perennial tree parts and approximately 30% greater removal of K in annual organs during ‘on’ than ‘off’ years suggests that K uptake could be 4 times higher in ‘on’ year trees than in (non-cropping), ‘off’ year trees.     

Soil nutrient status after bamboo flowering and death in a seasonal tropical forest in western Thailand

We have examined the surface (0–10 cm) soil characteristics of sites after bamboo (Cephalostachyum pergracile) mass flowering and death (DB sites) in comparison with sites with living bamboo (Bambusa tulda) (LB sites) in a seasonal tropical forest in Thailand. One year after bamboo flowering the DB sites were acidic with lower concentrations of exchangeable Ca and Mg and soil nitrogen than the LB sites. Therefore, although leaf and root litter of the dead bamboo was deposited in the DB sites after bamboo flowering, soil nutrient status decreased.     

Numerical modelling of shape regulation and growth stresses in trees

The main objective of this paper is to present the results of a study of the interactions between the growth and design of a tree with regards to biomechanical factors at the plant level. A numerical incremental model dedicated to the calculation of tree mechanical behaviour has been integrated in the plant architecture simulation software AMAPpara. At any stage of tree growth, a new equilibrium was calculated considering the weight increment applied on the structure, i.e. the mass of new wood layers and vegetative elements, as well as the biomechanical reaction caused by cell maturation strains in both normal and reaction wood. The resulting incremental displacements allowed the tree shape to be modified. The field of growth stresses was calculated within the stem, using a cumulative process taking into consideration the past history of each growth ring. The simulation results of trunk and branch shape, as well as internal stresses, were examined after consideration of different growth strategies. A block of trees was also simulated in order to show the influence of spatial competition on stem curvature and the variability in growth stress.     

Numerical modelling of shape regulation and growth stresses in trees

This paper is the first of a series focusing on the biomechanical analysis of live trees. The finite element method (fem) is the most common method used for the analysis of complex mechanical structures. Several fem industrial codes exist, but they need to be adapted to calculate the mechanical behaviour of growing trees. A general incremental model has been developed for this specific application. In this model, time was discretised and for any developmental stage, a new equilibrium was written considering the increment of weight due to the mass of new wood layers and new vegetative elements being added. Maturation strains of new-formed cells were also considered for the simulation of the shoot reorientation process. This model was intended for use at the whole plant level. A multi-layer beam finite element is presented, which is well adapted to discretise tree limbs. The shape evolution of the structure was represented at each time step by the nodal displacement vector. The mechanical stresses induced as a result of growth were determined within the stem using a cumulative process taking into account the past history of each growth ring. The first basic results of growth stresses and shape evolution were compared with already published results at the branch level.     

Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure

Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem.