Seed-to-seedling transitions exhibit distance-dependent mortality but no strong spacing effects in a Neotropical forest

Consequences of Local Conspecific Density Effects for Plant Diversity and Community Dynamics

Conspecific density dependence (CDD) in plant populations is widespread, most likely caused by local-scale biotic interactions, and has potentially important implications for biodiversity, community composition, and ecosystem processes. However, progress in this important area of ecology has been hindered by differing viewpoints on CDD across subfields in ecology, lack of synthesis across CDD-related frameworks, and misunderstandings about how empirical measurements of local CDD fit within the context of broader ecological theories on community assembly and diversity maintenance. Here, we propose a conceptual synthesis of local-scale CDD and its causes, including species-specific antagonistic and mutualistic interactions. First, we compare and clarify different uses of CDD and related concepts across subfields within ecology. We suggest the use of local stabilizing/destabilizing CDD to refer to the scenario where local conspecific density effects are more negative/positive than heterospecific effects. Second, we discuss different mechanisms for local stabilizing and destabilizing CDD, how those mechanisms are interrelated, and how they cut across several fields of study within ecology. Third, we place local stabilizing/destabilizing CDD within the context of broader ecological theories and discuss implications and challenges related to scaling up the effects of local CDD on populations, communities, and metacommunities. The ultimate goal of this synthesis is to provide a conceptual roadmap for researchers studying local CDD and its implications for population and community dynamics.

Significance of seed dispersal by the largest frugivore for large-diaspore trees

How do large-bodied frugivores contribute to seed dispersal of large-diaspore plants? This study examined seed dispersal effectiveness for two large-diaspore tree species, Astrotrichilia asterotricha (AA) and Abrahamia deflexa (AD), in a Madagascan forest. I evaluated fruit removal rates through focal tree observations and factors affecting seedling recruitment up to the 2-year-old seedling stage. I confirmed brown lemur (Eulemur fulvus) as the sole disperser, removing 58.8% and 26.0% of fruits produced by AA and AD. Brown lemurs frequently visited large-crowned AA trees with high density of fallen fruits and more adjacent fruiting trees during seasons with low fruit diversity. Most AA seedlings were removed by predators, although canopy openness slightly improved seedling establishment. Although AD seeds were severely attacked by predators under mother trees, the seedlings survived under dispersal conditions distant from the mother trees, and with low density of diaspores. AD had a higher cumulative probability from fruit removal to seedling recruitment (6.5%) than AA (1.5%) in the first rainy season. This study clarifies the significance of seed dispersal to tree recruitment strategies, which vary among different combinations of tree species and large frugivores, i.e. quantitative dispersal to reach suitable microhabitats, and qualitative dispersal to escape from dangerous zones near mother trees.

Measuring epistemic success of a biodiversity citizen science program: A citation study

This paper offers a comparative evaluation of the scientific impact of a citizen science program in ecology, ‘‘Vigie-Nature”, managed by the French National Museum of Natural History. Vigie-Nature consists of a national network of amateur observatories dedicated to a participative study of biodiversity in France that has been running for the last twenty years. We collected 123 articles published by Vigie-Nature in international peer-reviewed journals between 2007 and 2019, and computed the yearly amount of citations of these articles between 0–12 years post-publication. We then compared this body of citations with the number of yearly citations relative to the ensemble of the articles published in ecology and indexed in the ‘‘Web of Science” data-base. Using a longitudinal data analysis, we could observe that the yearly number of citations of the Vigie-Nature articles is significantly higher than that of the other publications in the same domain. Furthermore, this excess of citations tends to steadily grow over time: Vigie-Nature publications are about 1.5 times more cited 3 years after publication, and 3 times more cited 11 years post-publication. These results suggest that large-scale biodiversity citizen science projects are susceptible to reach a high epistemic impact, when managed in specific ways which need to be clarified through further investigations.

At 50, Janzen–Connell Has Come of Age

Fifty years ago, Janzen (1970) and Connell (1971) independently published a revolutionary idea to explain the hyperdiverse tree communities of the tropics. The essential observations were that seedfall is concentrated in the vicinity of fruiting trees, whereas saplings recruit at a distance from reproductive conspecifics. These observations were encapsulated in a simple focal-tree model constructed of intersecting curves for seedfall and escape from host-specific enemies postulated to attack propagules (seeds and seedlings) in the vicinity of reproductive conspecifics. In conflict with the thinking of the times, the mechanism operates from the top down rather than from the bottom up. A deterrent to broad acceptance has been the giant intuitive leap required to generalize the focal tree model to an entire forest community. Recent theoretical and empirical results have succeeded in bridging the gap between the focal tree model and its community-level implications. With these new findings, Janzen–Connell has come of age.