Understanding the design of warning signals: a predator’s view

Animal warning signals show remarkable diversity, yet subjectively appear to share visual features that make defended prey stand out and look different from more cryptic palatable species. Here we develop and apply a computational model that emulates avian visual processing of pattern and colour to Lepidopteran wing patterns to show that warning signals have specific neural signatures that set them apart not only from the patterns of undefended species but also from natural scenes. For the first time, we offer an objective and quantitative neural-level definition of warning signals based on how the pattern generates neural activity in the brain of the receiver. This opens new perspectives for understanding and testing how warning signals function and evolve, and, more generally, how sensory systems constrain general principles for signal design.

Changes in Vegetation of Flooded Savannas Subject to Cattle Grazing and Fire in Plains of Colombia

Cattle grazing and fire are common types of management on natural ecosystems, generating several threats to the conservation of native vegetation (e.g., changes in species richness, cover, and abundance, mainly of bovine-palatable species). In this work, we analysed the response of the structure and composition of vegetation managed with different cattle stocking rates and fire in the savanna ecosystems of Colombia. The study was located in the eastern area of the Llanos region, where savannas were subjected to grazing and burning. Regarding grazing, we classified the area according to the cattle stocking rate (Bos indicus ~300 kg): NG = non-grazed, LS = low stocking rate (0.5 ind ha−1 yr−1), and HS = high stocking rate (1.0 ind ha−1 yr−1). Controlled artificial burning was applied in all the area at the beginning of the study, and surveys were conducted in the same plots at pre-burn (t0) and four post-burn times (t1, t2, t3, t4), at 15, 45, 75 and 105 days after burning. Vegetation composition (species list, life-form, palatability) and structure (bare soil and vascular plant ground covers, species height and richness) were recorded at each sampling. Data were compared through ANOVAs and multivariate analyses. We found 53 species in total: 26 in the pre-burn treatment and 44 in the post-burn treatments, detecting an increase of 18 species considering all treatments. Seven natives and two exotic species represented the dominant cover (>50%). LS and HS had the highest number of palatable species in t0 (seven species) compared with NG (two species), but this became similar after burning (14 species in NG, 12 in LS, and 11 in HS). ANOVAs and multivariate analyses showed that plant assemblages were significantly different according to the grazing treatment, and more homogeneous in pre-burn than in post-burn periods. Cattle grazing favored higher covers of dominant palatable species (e.g., Axonopus purpusii) compared with NG, but many native species with high palatability only recovered within the system after burning. In the context of the current management proposals, the search for new alternatives other than intensive cattle grazing and burning is needed to reconcile human production activities, international commitments against climate change and biodiversity conservation in the savanna landscapes.

Caractérisation des pâturages herbacés sahéliens à accès limité : Cas du Centre Secondaire de Multiplication de Bétail de Sayam (Diffa).

Objectifs : Cette étude vise à caractériser l’état actuel des pâturages herbacés du Centre Secondaire de Multiplication de Bétail de Sayam. Méthodologie et Résultats : Quatre groupements pastoraux ont été identifiés et décrits à partir de 56 relevés linéaires réalisés sur un transect Sud - Nord. Au total 98 espèces herbacées réparties parmi 59 genres et 27 familles botaniques ont été répertoriées. Les genres suivants : Eragrostis, Ipomoea, Aristida, Cenchrus, Indigofera, Digitaria et Brachiaria ont été les mieux représentés. Ils représentent environ 50% du total et renferment l’essentiel des espèces de bonne valeur pastorale. Le recouvrement global, les valeurs pastorales brutes et nettes sont respectivement de 85,5%, 75,05% et 67,56%, celles-ci attestent que le pâturage du centre est de bonne qualité. La productivité globale en phytomasse herbacée a été estimée 2,26 tMS/ha avec une capacité de charge globale de 0,40 UBT/ha/an soit 2,5 ha/UBT/an. L’analyse du spectre fourrager indique que les espèces de bonne valeur pastorale et de faible valeur pastorale dominent le tapis herbacé. La première catégorie domine la zone centrale mieux protégée tandis que la dernière occupe les parties périphériques soumises à une forte exploitation du bétail. Conclusion et application des résultats : Le front de colonisation des espèces faiblement appétées (espèces qui ont IS = 0 ou IS = 1) progresse vers le centre sous l’effet de la forte pression pastorale. D’où l’urgence de clôturer l’ensemble du périmètre du centre afin d’éviter de créer un déséquilibre écologique préjudiciable à la survie de nombreuses espèces inféodées à ces milieux particuliers. Dans les perspectives d’une gestion durable des ressources fourragères des centres secondaire de multiplication de bétail, ce travail fournit des informations scientifiques fiables sur l’état actuel des pâturages herbacés de ce centre. Mots-clés : Kouri, composition floristique, groupements pastoraux, qualité pastorale, Sayam. Idrissa et al., J. Appl. Biosci. 2020 Caractérisation des pâturages herbacés sahéliens à accès limité : Cas du Centre Secondaire de Multiplication de Bétail de Sayam (Diffa). 16096 Characterization of Sahelian herbaceous pastures with limited access: Case of the Secondary Cattle Multiplication Center of Sayam (Diffa). ABSTRACT Objectives : This study aims to characterize the current state of the herbaceous pastures of the Sayam Secondary Cattle Multiplication Center. Methodology and Results : Four pastoral groups have been identified and described from 56 linear surveys carried out on a South - North transect. A total of 98 herbaceous species distributed among 59 genera and 27 botanical families have been listed. The best represented genera are: Eragrostis, Ipomoea, Aristida, Cenchrus, Indigofera, Digitaria and Brachiaria. They represent about 50% of the total and contain most of the species of good pastoral value. The overall recovery, the gross and net pastoral values are respectively 85.5%, 75.05% and 67.56%, these attest that the pasture of the center is of good quality. The overall productivity of herbaceous phytomass was estimated at 2.26 tMS / ha with an overall carrying capacity of 0.40 TLU / ha / year, ie 2.5 ha / TLU / year. Analysis of the forage spectrum indicates that species of good pastoral value and those of low pastoral value dominate the grass cover. The first category dominates the better protected central zone while the last occupies the peripheral parts subject to heavy livestock exploitation. Conclusion and applicability of results : The colonization front of poorly palatable species is progressing towards the center under the effect of strong pastoral pressure. Hence the urgency to enclose the entire perimeter of the center in order to avoid creating an ecological imbalance detrimental to the survival of many species dependent on these particular miles. With a view to the rehabilitation and sustainable management of these pastoral centers, this study provides additional information on the current state of the herbaceous pastures in this center. Keywords : Kouri, floristic composition, pastoral groups, pastoral quality, Sayam, Niger

Germination characteristics and phytotoxic inhibition of germination in Artemisia adamsii, a low-palatability weed in the Mongolian steppe

Artemisia adamsii is a weed with low palatability to livestock and is thus recognized as an indicator of rangeland degradation in Mongolia. We investigated the germination characteristics of this species, phytotoxic suppression of its germination by its own residue, and the applicability of such germination behaviour to the control of this species. We also discussed the ecological consequence of these factors regarding the vegetation dynamics of the Mongolian steppe. Germination of A. adamsii was tested at different light and temperature conditions. Germination was also tested for A. adamsii and four native grassland species in the presence or absence of A. adamsii residue. Germination of A. adamsii was light-demanding and temperature-dependent. Artemisia adamsii residue showed autotoxic but sub-fatal suppression of germination, and the chemicals causing that suppression were shown to be aqueous and volatile. Phytotoxicity of A. adamsii residue on the germination of grassland species was low, except for in Artemisia frigida. The applicability of the observed sub-fatal autotoxicity for controlling this species was likely to be low, but the elucidated germination characteristics could contribute to developing a strategy for controlling this species. The autotoxicity in A. adamsii germination was suggested to have an ecological consequence that mediates species transition from A. adamsii to other species in degraded land occupied by A. adamsii. As low-palatability A. adamsii can act as a nurse plant of palatable species under grazing conditions, the invasion of A. adamsii into disturbed grasslands may facilitate the recovery of such grasslands in terms of improving pasture quality.

Effects of Grazing Exclusion on Biomass Growth and Species Diversity among Various Grassland Types of the Tibetan Plateau

Livestock grazing is an important determinant of species diversity and plant growth. Overgrazing is identified as one of the most important disturbances resulting in grassland degradation. Although many restoration practices have been implemented, grazing exclusion is one of the most effective methods to restore degraded grasslands. We explored the impact of five years of grazing exclusion on plant growth and species diversity in four types of grasslands: temperate steppe (TS), swamp meadow (SM), alpine steppe (AS), and alpine meadow (AM). Our results showed that grazing exclusion increased plant height, coverage, biomass, and species diversity in all four grasslands. The aboveground biomass in AM (180.8%), TS (117.3%), and SW (105.9%) increased significantly more than AS (10.1%). Grazing exclusion in AM had the greatest effect on proportion of palatable species, and the increase in palatable species in AM was higher than that of the other grassland types significantly. Species diversity increased significantly within the enclosure in SM (23.9%) and AM (20.8%). Our results indicate that grazing exclusion is an effective management strategy to restore degraded grasslands and it works best in alpine meadow. This study contributes to the growing theoretical basis for grassland management strategies and has a significant effect on sustainable development for grassland resources and pastoral areas.

Batesian mimicry and masquerade

This chapter concerns Batesian mimicry, which is the resemblance of a palatable species to an unpalatable or otherwise unprofitable species. Often these unprofitable models have warning signals, which the mimic has evolved to copy. The chapter also considers another well-known form of deception, namely masquerade, which is the resemblance of a palatable species to the cues of an object of no inherent interest to a potential predator such as leaves, thorns, sticks, stones, or bird droppings. Batesian mimicry and masquerade share many properties, and both can be considered examples of ‘protective deceptive mimicry’. We begin by briefly reviewing some well-known examples of protective deceptive mimicry. We then compare and contrast the various theories that have been proposed to understand them. Next, we examine the evidence for the phenomenon and its predicted properties, and finally we address several important questions and controversies, many of which remain only partly resolved.

Grazing elevates litter decomposition but slows nitrogen release in an alpine meadow

Nutrient cycling is a key ecosystem function whereby the processes of litter decomposition and N release in the soil-plant interface are vitally important but still not clear in the alpine ecosystems. We carried out a 3-year study to improve our understandings in nutrient cycle and develop strategies for restoring the degraded grasslands on the Qinghai-Tibetan Plateau. We established the grazing (GP) and grazing exclusion paddocks (GEP), then identified litter species composition and analyzed litter and soil chemical characteristics. Litter decomposition and N release were monitored by incubating litter in situ and across paddocks over 799 days. We found that grazing did not change plant species composition, but increased litter N; while grazing exclusion increased litter mass of palatable species and promoted soil organic carbon. Litter decomposed faster in GP, while N release was faster in GEP. Incubation site environment had more but litter source had less impact on litter decomposition and N release. Therefore, grazing and grazing exclusion had different impacts on litter decomposition and N release but both elevated nutrient cycle. The implications of our findings in restoring the degraded grasslands on the Qinghai-Tibetan Plateau were discussed.

Walking like an ant: a quantitative and experimental approach to understanding locomotor mimicry in the jumping spider Myrmarachne formicaria

Protective mimicry, in which a palatable species avoids predation by being mistaken for an unpalatable model, is a remarkable example of adaptive evolution. These complex interactions between mimics, models and predators can explain similarities between organisms beyond the often-mechanistic constraints typically invoked in studies of convergent evolution. However, quantitative studies of protective mimicry typically focus on static traits (e.g. colour and shape) rather than on dynamic traits like locomotion. Here, we use high-speed cameras and behavioural experiments to investigate the role of locomotor behaviour in mimicry by the ant-mimicking jumping spider Myrmarachne formicaria , comparing its movement to that of ants and non-mimicking spiders. Contrary to previous suggestions, we find mimics walk using all eight legs, raising their forelegs like ant antennae only when stationary. Mimics exhibited winding trajectories (typical wavelength = 5–10 body lengths), which resemble the winding patterns of ants specifically engaged in pheromone-trail following, although mimics walked on chemically inert surfaces. Mimics also make characteristically short (approx. 100 ms) pauses. Our analysis suggests that this makes mimics appear ant-like to observers with slow visual systems. Finally, behavioural experiments with predatory spiders yield results consistent with the protective mimicry hypothesis. These findings highlight the importance of dynamic behaviours and observer perception in mimicry.

Changes in understory species occurrence of a secondary broadleaved forest after mass mortality of oak trees under deer foraging pressure

The epidemic of mass mortality of oak trees by Japanese oak wilt has affected secondary deciduous broadleaved forests that have been used as coppices in Japan. The dieback of oak trees formed gaps in the crown that would be expected to enhance the regeneration of shade-intolerant pioneer species. However, foraging by sika deerCervus nipponhas also affected forest vegetation, and the compound effects of both on forest regeneration should be considered when they simultaneously occur. A field study was conducted in Kyôto City, Japan to investigate how these compound effects affected the vegetation of the understory layer of these forests. The presence/absence of seedlings and saplings was observed for 200 quadrats sized 5 m ×5 m for each species in 1992, before the mass mortality and deer encroachment, and in 2014 after these effects. A hierarchical Bayesian model was constructed to explain the occurrence, survival, and colonization of each species with their responses to the gaps that were created, expanded, or affected by the mass mortality ofQuercus serratatrees. The species that occurred most frequently in 1992,Eurya japonica,Quercus glauca, andCleyera japonica, also had the highest survival probabilities. Deer-unpalatable species such asSymplocos prunifoliaandTriadica sebiferahad higher colonization rates in the gaps, while the deer-palatable speciesAucuba japonicahad the smallest survival probability. The gaps thus promoted the colonization of deer-unpalatable plant species such asSymplocos prunifoliaandTriadica sebifera. In the future, such deer-unpalatable species may dominate gaps that were created, expanded, or affected by the mass mortality of oak trees.