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Offspring from elderly parents often have lower survival due to parental senescence. In cooperatively breeding species, where offspring care is shared between breeders and helpers, the alloparental care provided by helpers is predicted to mitigate the impact of parental senescence on offspring provisioning and, subsequently, offspring survival. We test this prediction using data from a long-term study on cooperatively breeding Seychelles warblers (Acrocephalus sechellensis). We find that the nestling provisioning rate of female breeders declines with their age. Further, the total brood provisioning rate and the first-year survival probability of offspring decline progressively with age of the female breeder, but these declines are mitigated when helpers are present. This effect does not arise because individual helpers provide more care in response to the lower provisioning of older dominant females, but because older female breeders have recruited more helpers, thereby receiving more overall care for their brood. We do not find such effects for male breeders. These results indicate that alloparental care can alleviate the fitness costs of senescence for breeders, which suggests an interplay between age and cooperative breeding.

Ecological speciation is facilitated when divergent adaptation has direct effects on selective mating. Divergent sensory adaptation could generate such direct effects, by mediating both ecological performance and mate selection. In aquatic environments, light attenuation creates distinct photic environments, generating divergent selection on visual systems. Consequently, divergent sensory drive has been implicated in the diversification of several fish species. Here, we experimentally test whether divergent visual adaptation explains the divergence of mate preferences in Haplochromine cichlids. Blue and red Pundamilia co‐occur across south‐eastern Lake Victoria. They inhabit different photic conditions and have distinct visual system properties. Previously, we documented that rearing fish under different light conditions influences female preference for blue versus red males. Here, we examine to what extent variation in female mate preference can be explained by variation in visual system properties, testing the causal link between visual perception and preference. We find that our experimental light manipulations influence opsin expression, suggesting a potential role for phenotypic plasticity in optimizing visual performance. However, variation in opsin expression does not explain species differences in female preference. Instead, female preference covaries with allelic variation in the long‐wavelength‐sensitive opsin gene (LWS), when assessed under broad‐spectrum light. Taken together, our study presents evidence for environmental plasticity in opsin expression and confirms the important role of colour perception in shaping female mate preferences in Pundamilia. However, it does not constitute unequivocal evidence for the direct effects of visual adaptation on assortative mating., Pundamilia cichlids exhibit light‐induced opsin expression plasticity, which correlates with female mate preference, but does not explain species differences in preference. Instead, female preference covaries with allelic variation in the LWS opsin in broad‐spectrum light, confirming the important role of colour perception in shaping Pundamilia mate preferences.

In northern Burkina Faso (West Africa), a study was undertaken to explore the possibilities of restoring the infiltration capacity of crusted soils through the stimulation of termite activity. Treatments consisted of the application of a mulch of a mixture of wood and straw without insecticides (resulting in “termite plots”) and the application of the same mulch and an insecticide (Dursban with chloropyrifos as the active ingredient) to prevent termite activity (resulting in “non-termite plots”). Three rainfall simulations of 60 minutes duration with an intensity of 50 mm/h at an interval of 24 hours between the first and the second and 72 hours between the second and third simulation were applied, to study the effect of consecutive showers on termite-modified soil characteristics. Cumulative infiltration amounts, final infiltration rates, soil water content and porosity were larger and bulk density was smaller on termite plots as compared to non-termite plots. This suggests that termites may be an important agent in soil-crust control and in the improvement of soil physical properties in Sahelian ecosystems.

According to classical exploitation theory, an increase of primary productivity should result in increased herbivore grazing pressure, thus maintaining a low plant standing crop, However, field data obtained from a salt marsh revealed a maximal grazing pressure by hares, rabbits, and geese at intermediate levels of plant standing crop. Grazing pressure was relatively low in the more productive parts. We argue that this pattern is due to a low foraging efficiency of these herbivores in dense vegetation. In order to investigate this hypothesis, we examine a plant-herbivore model where grazing becomes less efficient in dense vegetation, and analyze the behavior of this model along a gradient of primary productivity. In systems of intermediate productivity, the model predicts that a plant-herbivore system may have two stable states. In one state, the herbivore maintains a low standing crop. The other state is dominated by a dense vegetation unsuitable for herbivore grazing. In systems of high productivity, the herbivore is unable to keep plant growth in check and a dense vegetation develops. Thus, in line with our field data but in contrast to classical exploitation theory, our model does not predict ''top-down'' control in productive environments.

Summary We present the results of a histochemical study comparing seedlings of races C and D of Orobanche cumana Wallr. (syn. O. cernua Loefl.) attacking sunflower (Helianthus annuus L.) in southern Russia. Three groups of O. cumana seedlings were distinguished according to the peroxidase content of the cells in the radicles: (1) those with neither extracellular nor intracellubr peroxidase and whose radicles have a smooth apex (these were classified as non-infective): (2) those with a high peroxidase content of the nuclei and the cytoplasm layer adjacent to the cell wall, as well as excretion of peroxidase from the apex of the radicles: (3) those with a similarly high peroxidase activity in the parasite cells, but without extracellular excretion. The apices of the radicles of the last two groups are swollen. It is suggested that these belong to O. cumana races C and D respectively. The extracellular peroxidase in O. cumana race C reacts with phenolic compounds, which are lignin precursors of the host, resulting in host resistance due to the formation of lignin layers in sunflowers possessing the Or3 gene for resistance. The absence of extracellular peroxidase in O. cumana race D prevents lignin formation and enables the parasite to attach to the host vascular system. Comparison of these data with the information on the earlier O. cumana races A and B, and older sunflower cultivars, points to a crucial role of peroxidase in the process of breeding new sunflower cultivars and the evolution of new O. cumana races.

The currently widespread abandoning of agricultural land use in Western Europe offers new opportunities for ecological restoration and nature conservation. This is illustrated for abandoned arable fields and for permanent grasslands cut for hay after the cessation of fertilizer application. Although initiated by a sudden reduction of nutrient input to the system, the changing nutrient supply from the soil is considered to be the main driving force of succession. The soil nutrient supply is affected by soil organisms, both directly (root symbionts and herbivores) and indirectly (nutrient mineralization from dead organic matter). It is argued that because of the close association of changes in species diversity with changes in the functioning of ecosystems, biodiversity has to be studied in an ecosystem ecology context.

Experiences with the reintroduction of the takhi, or Przewalski horse (Equus ferus przewalskii, in Mongolia can serve as valuable lessons for reintroduction of ungulates in general. We discuss the present taxonomic, historical, and biological evidence and conclude that the takhi should be viewed as a typical steppe herbivore. Its last refuge, the Dzungarian Gobi, should therefore be seen as a marginal habitat because it consists mainly of desert and semidesert. Since 1992 two reintroduction projects have been in the acclimatization phase in Mongolia. Despite promising developments, problems with cooperation, management, habitat choice, insufficient knowledge of the ethology of the species, and current land use within the different project areas could jeopardize the successful reintroduction of takhi. We review the conditions required for a potentially successful ungulate reintroduction. The planning of a reintroduction within the framework of safeguarding an entire ecosystem with an integrated management plan appears essential. Each potential reintroduction site should be assessed thoroughly for its suitability, including size, habitat types, current land use, socioeconomics, legislation, and potential problems. Each site should be provided with one or more acclimatization facilities to harbor genetically and physically healthy, socially adapted animals in biologically sound groups. An organization structure should be established for each reintroduction site. Its objective should be to develop an effective management plan and to carefully monitor the population and its surrounding ecosystem. Special attention should be given to local socioeconomic situations, community participation, and training of staff for management, research, and ranger and warden activities. Las experiencias de reintroduccion del pakhi o caballo Przewalski (Equus ferus przewalskii) en Mongolia pueden proporcionar lecciones valiosas para la reintroduccion de ungulados en general. Discutimos la taxonomia actual, evidencias historicas y biologicas y concluimos que el pakhi debe ser considerado como un herbivoro tipico de estepas. El Dzungarian Gobi, considerado su ultimo refugio, deberia ser visto como un habitat marginal puesto que consiste basicamente de areas deserticas y semideserticas. Desde 1992, dos proyectos de reintroduccion estan en su fase de aclimatacion en Mongolia. A pesrar de avances promisorios, problemas con cooperacion, manejo, seleccion de habitat, insuficiente conocimiento de la etologia de la especie y el actual uso del suelo dentro de las diferentes areas del proyecto podrian amenazar la reintroduccion exitosa del takhi. Las condiciones necesarias para una reintroduccon exitosa de ungulados son revisadas. La planeacion de una reintroduccion dentro de un marco de salvaguarda del ecosistema en su conjunto con un plan de manejo integrado parece ser esencial. La viabilidad de coda sitio potencial para reintroducciones debera ser evaluada rigurosamente considerando tamano, tipos de habitats, uso actual del suelo, aspectos socioeconomicos, legislacion y problemas potenciales. Cada sitio debera ser provisto con una o mas instalaciones para aclimatacion, para embarcar animales genetica y fisicamente sanos, socialmente adaptados en grupos biologicamente estables. Se debera establecer una estructura organizacional para cada sitio de reintroduccion, cuyo objectivo sera el de desarrollar un plan de manejo efectivo y monitorear la poblacion y el ecosistema que lo rodea. Se debera poner especial atencion a las situaciones socioeconomicas locales, la participacion de la comunidad y el entrenamiento de un grupo de trabajo para actividades de majo, investigacion y vigilancia.

Recently, several species of basidiomycetes were shown to produce de novo high concentrations of chloroaromatic metabolites. Since these lignocellulose-degrading fungi play a major role in the ecosphere, the purpose of this study was to determine the ubiquity of organohalogen production among basidiomycetes. A total of 191 fungal strains were monitored for adsorbable organic halogen (AOX) production when grown on defined liquid media. Approximately 50% of the strains tested and 55% of the genera tested produced AOX. A low production of 0.1–0.5 mg AOX/l was observed among 25% of the strains, a moderate production of 0.5–5.0 mg AOX/l was observed among 16% of the strains and 9% of the strains produced high levels (5–67 mg AOX/l). The latter group was dominated by species belonging to the genera Hypholoma, Mycena and Bjerkandera, showing specific AOX productions in the range 1074–30893 mg AOX/kg dry weight of mycelial biomass. Many highly ecologically significant fungal species were identified among the moderate to high producers. These species were also able to produce AOX when cultivated on natural lignocellulosic substrates. Hypholoma fasciculare and Mycena metata respectively produced up to 132 mg and 193 mg AOX/kg dry weight of forest litter substrate in 6 weeks.

1. Ungulates and forest management Forest management is currently undergoing major changes, both in Western Europe and in North Amer- ica (Von SchGppfer, 1983; Thomas, 1994). Forestry becomes more oriented towards ecosystem manage- ment, with natural processes promoted and indige- nous species and multi-species forest stands favoured. Strictly regulated, even-aged forestry practices are becoming less common. Forest clearfelling is prac- tised on a smaller scale, thus preventing major dis- turbance of the forest microclimate. Spontaneous regeneration is stimulated in commercial forests by partly thinning of canopies or by small clearcuts, and structural diversity of managed stands is enhanced. In this ‘nature-following forestry’, silvicultural treat- ments are carried out in such a way that the habitat of typical forest plants, wildlife, insects and microor- ganisms is less affected. Sustainable forestry and biodiversity are items of growing importance in this type of forest management. In addition, after decades of reduction, in most countries forest cover is ex- panding again, related to the set-aside of agricultural land and other land-use changes. These new goals in forest management have far- reaching implications for the area and quality of ungulate habitats, for the ungulate populations and for their management. In the past, large herbivorous mammals were often seen as ‘pest species’, conflict

This paper sets out that the dynamics of the Sahelian rangeland vegetation can be interpreted as a cusp catastrophe and that this interpretation offers a promising basis for the description and analysis of tbis ecosystem. Firstly, an existing scheme of the dynamics of Sahelian herbaceous vegetation is translated into the state-and-transition formulation. Secondly, the application of the cusp catastrophe is explored by studying the behaviour of the Sahelian rangeland ecosystem under changing effective rainfall and grazing inteusity, using the transitions from the state-and-transition formulation as vectors along the cusp manifold. This conceptual cusp catastrophe model subsequently results in the identification of hypotheses and the detection of 5 catastrophic properties of this ecosystem (biiodality, inaccessibiity, sudden jumps, divergence and hysteresis) that have important management implications. The continuous and the discontinuous processes occurring in the Sahelian rangeland ecosystem can both be captured in a tified conceptual model by applying the cusp catastrophe theory. Testing the hypotheses generated by the conceptual model and searching for additional catastrophic properties, such as divergence of linear response and critical slowing down, is a useful direction for future research

The importance of private and commercial harvest of wild edible mushrooms in Europe and North America is briefly outlined. Possible negative effects of harvesting on the production of sporocarps are discussed. There is no evidence that picking of mushrooms is harmful for subsequent fruiting, except in some cases where mycelia are destroyed. Changes in frequency of edible mushrooms in Europe are described with special emphasis on The Netherlands. The occurrence of edible species on Red Lists of threatened fungi in Europe is discussed. The decline of many ectomycorrhizal species is supposed to be mainly caused by environmental pollution. Relations between harvesting of edible mushrooms, forest management and nature conservation are indicated. Key words: edible mushrooms, mushroom picking, decline of fungi, forest management.

Soil microarthropod populations in maize plots mulched with the prunings of three woody agroforestry plant residues (Acioa barteri, Gliricidia sepium and Leucaena leucocephala) and two crop residues [maize (Zea mays) stover (leaves and stems) and rice (Oryza sativa) straw] were monitored throughout the 1991 growing season and compared with those in fallow, bare fallow and unmulched control plots with three rates of nitrogen application. The mean densities of detritivore and phytophage microarthropods in the experimental plots decreased in the following order: rice straw > Gliricidia prunings > Leucaena prunings > maize stover > Acioa prunings > control 2 (90 kg N ha-1 year-1) > fallow > control 3 (135 N) > control 1 (45N) > bare fallow. Mulching also affected the population dynamics of predatory microarthropods and omnivorous ants. The chemical composition of plant residues probably influenced the densities of detritivore and phytophage microarthropods, which in addition were also greatly influenced by microclimatic conditons imposed by vegetation cover. Extremely low densities of microarthropods were recorded in the bare fallow plots probably as a result of the combined effects of absence of plant residues and vegetation cover. The potential of mulching as a component of farming practice for increasing the density of microarthropods and for influencing their species composition and population dynamics in agroecosystems is discussed.

The effects of tropical earthworms ( Eudrilus eugeniae ) and millipedes (Spirostreptidae) on the breakdown of plant residues [ Acioa (presently, Dactyladenia) barteri, Gliricidia sepium and Leucaena leucocephala prunings, maize ( Zea mays ) stover and rice ( Oryza sativa ) straw], with contrating chemical compositions, were studied in the field under humid tropical circumstances. Addition of earthworms significantly increased the breakdown of maize stover. Addition of millipedes significantly increased the breakdown of maize stover and rice straw. Combined addition of earthworms and millipedes generally resulted in greater plant residue breakdown, compared to that of a single group of fauna. During 10 weeks of exposure, earthworms and millipedes, on average, accounted for the breakdown of all plant residues by 10.4 and 28.4%, respectively. Millipedes and earthworms contributed more to the breakdown of plant residues with low quality (high C-to-N ratio, lignin and polyphenol contents) than to the degradation of those with high quality. It is concluded that fauna-enhanced breakdown of plant residues will have different effects on soil nutrient supply, depending on residue quality.