Seed dispersal by vertebrates in Madagascar’s forests: review and future directions

Madagascar’s highly diverse forests are critically threatened because of increasing deforestation, and those that remain are facing declines of vertebrate frugivores that disperse their seeds. Thus, understanding plant - frugivore interactions is of critical importance for the conservation and maintenance of plant diversity in Madagascar. This paper reviews observational and experimental studies of the multifaceted aspects of seed dispersal by vertebrates across Madagascar including the relative importance of different seed vectors, the patterns of seed deposition, and the post - dispersal fate of dispersed seeds. This also aims to lay a foundation for future studies by discussing understudied aspects that are crucial for the understanding of the role of frugivores on plant populations and communities in Malagasy forests. Such perspectives are important given the increasing threats to seed dispersers, the low richness of frugivore assemblages in Malagasy forests and the strong reliance of many plant species on frugivores for their dispersal. Understanding this ecosystem service can provide us insights on plant colonization, community structure, demography and invasion, as well as forest restoration and regeneration.   RÉSUMÉ Les forêts de Madagascar abritent des communautés de plantes vasculaires exceptionnellement diverses avec un taux d’endémisme s’élevant à 82 %. Malheureusement, hormis les continuelles dégradation et fragmentation menaçant ces forêts, la flore malgache est aussi menacée par l’insuffisance et le déclin des populations d’animaux frugivores qui jouent un rôle fondamental dans la dissémination des graines. La compréhension de ce mécanisme de dissémination des graines par des frugivores est importante pour savoir comment préserver la biodiversité et la régénération forestière ainsi que pour établir des stratégies de conservation des habitats fragmentés. Le présent article constitue une synthèse des publications scientifiques sur les recherches concernant ce mécanisme dans les forêts malgaches. Les informations disponibles sont plutôt limitées mais suggèrent que la majorité des plantes malgaches dépendent des vertébrés frugivores pour la dissémination de leurs graines. Ces études montrent également quelques aspects portant sur des modèles de dispersion des graines et des plantules. Plusieurs éléments relatifs à ce mécanisme sont encore inconnus et nécessitent des recherches approfondies. Les pressions menaçant les différents vecteurs de graines sont discutées, et plus particulièrement celles qui pourraient avoir des effets néfastes sur la démographie des populations de plantes. En outre, des recommandations sont formulées pour permettre l’intégration des interactions frugivore–plante dans la conservation des écosystèmes forestiers malgaches.

Assessing the challenges and initiatives to increase women’s integration into science in Madagascar

We present here a commentary essay on the challenges and perspectives on the recruitment and retention of Malagasy women in STEM (Science, Technology, Engineering, and Mathematics). We base the essay on our personal experience as Malagasy women scientists and support the arguments with the responses of 60 Malagasy women scientists to an online survey that was shared among Malagasy scientists. We identified that the main causes for a limited number of Malagasy women in STEM relied upon traditional expectations and heavily ingrained cultural values. The situation becomes more complicated when accounting for familial constraints, financial constraints, and communication gaps between students and professors. This is obviously an unfortunate situation; however, there have been bridging-gap initiatives—financial, awareness to family pressure, and knowledge difference between senior and junior scientists—that should be continued to provide support to promising students and enhance STEM education as a tool for development in Madagascar. RésuméCet essai discute les défis et les perspectives dans le recrutement et le maintien des femmes citoyennes de Madagascar dans les sciences, la technologie, l’ingénierie et les mathématiques (STIM). Les arguments présentés sont basés sur nos expériences personnelles en tant que femmes scientifiques nées et ayant grandies à Madagascar. Ces arguments sont soutenus par des informations issues d’un sondage effectué en ligne auprès de 60 femmes scientifiques, s’identifiant elles-mêmes originaires de Madagascar. Les raisons pour lesquelles ces femmes sont peu nombreuses à participer activement dans les domaines des STIM à Madagascar sont liées à des contraintes traditionnelles et à des valeurs culturelles fortement ancrées depuis leur enfance. La situation se complique lorsqu’on tient compte des contraintes financières et des écarts de communication entre étudiants et professeurs. Si cette situation est évidemment regrettable, il existe cependant des initiatives visant à combler le fossé qui sont financières, ou qui s’inscrivent dans la sensibilisation à la pression familiale et à la différence de connaissances entre les scientifiques seniors et juniors. Ces encouragements devraient être poursuivis afin d'apporter un soutien aux étudiantes prometteuses et d'améliorer l'enseignement des femmes en STIM qui sont importantes pour le développement de Madagascar

Edge effects on components of diversity and above-ground biomass in a tropical rainforest

Edge effects are among the most significant consequences of forest fragmentation. Therefore, understanding the impacts of edge creation on biodiversity is crucial for forest management and biological conservation. In this study, we used trait‐based and phylogenetic approaches to examine the effects of fragmentation on components of diversity and above‐ground biomass of rainforest tree communities in Madagascar in forest edge vs. interior habitats. Tree communities in forest edges showed lower phylogenetic diversity relative to those in interior habitats, suggesting that some clades may be more vulnerable to environmental filtering than others. Functional diversity was also significantly lower on the edge for productivity traits, but not for dispersal traits. Tree communities in the forest edge showed higher divergence of dispersal traits and lower divergence in productivity traits than expected, while functional diversity in interior forest did not differ from random expectations. This suggests that separate mechanisms affect productivity traits vs. dispersal traits in edge habitats. There was no significant difference in above‐ground biomass between edge and interior habitats, suggesting that edge effects have not yet negatively influenced the forest's potential for carbon storage. However, these changes may not have occurred yet, given the slow turnover of tree communities. Synthesis and applications. Our results highlight the role of edge effects in the erosion of functional and phylogenetic diversity of highly diverse tree communities. While above‐ground biomass did not appear to be affected by forest edge in our study, we suggest long‐term monitoring of forests for potential changes in ecosystem functioning. These findings also indicate the need to reduce edge creation and buffer existing edges for holistic biodiversity conservation

The total dispersal kernel: a review and future directions

The distribution and abundance of plants across the world depends in part on their ability to move, which is commonly characterized by a dispersal kernel. For seeds, the total dispersal kernel (TDK) describes the combined influence of all primary, secondary and higher-order dispersal vectors on the overall dispersal kernel for a plant individual, population, species or community. Understanding the role of each vector within the TDK, and their combined influence on the TDK, is critically important for being able to predict plant responses to a changing biotic or abiotic environment. In addition, fully characterizing the TDK by including all vectors may affect predictions of population spread. Here, we review existing research on the TDK and discuss advances in empirical, conceptual modelling and statistical approaches that will facilitate broader application. The concept is simple, but few examples of well-characterized TDKs exist. We find that significant empirical challenges exist, as many studies do not account for all dispersal vectors (e.g. gravity, higher-order dispersal vectors), inadequately measure or estimate long-distance dispersal resulting from multiple vectors and/or neglect spatial heterogeneity and context dependence. Existing mathematical and conceptual modelling approaches and statistical methods allow fitting individual dispersal kernels and combining them to form a TDK; these will perform best if robust prior information is available. We recommend a modelling cycle to parameterize TDKs, where empirical data inform models, which in turn inform additional data collection. Finally, we recommend that the TDK concept be extended to account for not only where seeds land, but also how that location affects the likelihood of establishing and producing a reproductive adult, i.e. the total effective dispersal kernel

Advancing an interdisciplinary framework to study seed dispersal ecology

Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant’s life history and environmental variability that ultimately influences a population’s ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity

Employing plant functional groups to advance seed dispersal ecology and conservation

Seed dispersal enables plants to reach hospitable germination sites and escape natural enemies. Understanding when and how much seed dispersal matters to plant fitness is critical for understanding plant population and community dynamics. At the same time, the complexity of factors that determine if a seed will be successfully dispersed and subsequently develop into a reproductive plant is daunting. Quantifying all factors that may influence seed dispersal effectiveness for any potential seed-vector relationship would require an unrealistically large amount of time, materials and financial resources. On the other hand, being able to make dispersal predictions is critical for predicting whether single species and entire ecosystems will be resilient to global change. Building on current frameworks, we here posit that seed dispersal ecology should adopt plant functional groups as analytical units to reduce this complexity to manageable levels. Functional groups can be used to distinguish, for their constituent species, whether it matters (i) if seeds are dispersed, (ii) into what context they are dispersed and (iii) what vectors disperse them. To avoid overgeneralization, we propose that the utility of these functional groups may be assessed by generating predictions based on the groups and then testing those predictions against species-specific data. We suggest that data collection and analysis can then be guided by robust functional group definitions. Generalizing across similar species in this way could help us to better understand the population and community dynamics of plants and tackle the complexity of seed dispersal as well as its disruption

Data from: Co-fruiting plant species share similar fruit and seed traits while phylogenetic patterns vary through time

1.Co-fruiting plant species are subject to a variety of biotic and abiotic processes that may influence patterns of fruiting phenology and the functional and phylogenetic diversity of co-fruiting taxa in a community. Understanding the seasonal patterns of functional and phylogenetic diversity of fruiting in a community will shed new light on potential mechanisms structuring plant communities. 2.Using rainforest trees in south-eastern Madagascar as our system, we predicted there would be clustering of fruit and seed traits and phylogenetic relationships among co-fruiting species because plants are vying for seed dispersal services from a limited set of generalist frugivore taxa. We also predicted that seasonal variations in rainfall would mediate fluctuations in functional trait and phylogenetic diversity of co-fruiting assemblages. 3.Despite fluctuating patterns in their functional trait diversity over time, co-fruiting assemblages displayed consistent clustering of fruit/seed traits across time. Phylogenetic diversity was not clustered overall, but fluctuated non-randomly, in time between clustered and overdispersed, such that strong shifts in rainfall were associated with the co-fruiting of more closely related species. 4.Synthesis: We suggest that it may be more beneficial for co-fruiting plant species to share similar fruit and seed traits than to diversify traits, when they rely on a comparatively small set of generalist frugivorous taxa for seed dispersal. Results also demonstrate that rainfall-driven environmental filtering may cause seasonal fluctuations in the phylogenetic patterns of phenology in a community. Results highlight the importance of a temporal context in examining structural patterns of communities