Neighbourhood effects on plant reproduction: An experimental-analytical framework and its application to the invasive Senecio inaequidens

1. Density dependence is of fundamental importance for population and range dynamics. Density-dependent reproduction of plants arises from competitive and facilitative plant-plant interactions that can be pollination independent or pollination mediated. In small and sparse populations, conspecific d...

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Bibliographic Details
Published in:The Journal of ecology 2018-03, Vol.106 (2), p.761-773
Main Authors: Lachmuth, Susanne, Henrichmann, Colette, Horn, Juliane, Pagel, Jörn, Schurr, Frank M.
Format: Article
Language:English
Subjects:
Allee effect
Availability
biological invasion
competition
Composition
Density dependence
Dynamics
facilitation
Frameworks
Herbivores
Interactions
Introduced species
Invasive species
Observational studies
Plant communities
Plant populations
Plant reproduction
Plant-plant interactions
Planting density
Pollen
Pollination
Pollinators
Population decline
Population density
Populations
Range extension
Reproduction
reproductive success
Residential density
Seed set
Senecio
spatially explicit model
trait‐based neighbourhood model
Transplantation
Wildlife conservation
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Summary:1. Density dependence is of fundamental importance for population and range dynamics. Density-dependent reproduction of plants arises from competitive and facilitative plant-plant interactions that can be pollination independent or pollination mediated. In small and sparse populations, conspecific density dependence often turns from negative to positive and causes Allee effects. Reproduction may also increase with heterospecific density (community-level Allee effect), but the underlying mechanisms are poorly understood and the consequences for community dynamics can be complex. Allee effects have crucial consequences for the conservation of declining species, but also the dynamics of range edge populations. In invasive species, Allee effects may slow or stop range expansion. 2. Observational studies in natural plant communities cannot distinguish whether reproduction is limited by pollination-mediated interactions among plants or by other neighbourhood effects (e.g. competition for abiotic resources). Even experimental pollen supply cannot distinguish whether variation in reproduction is caused by direct density effects or by plant traits correlated with density. Finally, it is unknown over which spatial scales pollination-mediated interactions occur. 3. To circumvent these problems, we introduce a comprehensive experimental and analytical framework which simultaneously (1) manipulates pollen availability and quality by hand pollination and pollinator exclusion, (2) manipulates neighbourhoods by transplanting target plants, and (3) analyses the effects of con- and heterospecific neighbourhoods on reproduction with spatially explicit trait-based neighbourhood models. 4. Applying this framework to Senecio inaequidens, one of Europe's fastest plant invaders, we found that the seed set was strongly pollen limited. Reproduction had increased by pollinator-mediated facilitation by both con- and heterospecific neighbours which may lead to (community-level) Allee effects. Pollination-independent interactions, such as amelioration of abiotic conditions through neighbours, contributed to additional positive neighbour effects. However, these pollination-independent interactions were weaker than the pollination-mediated interactions and they occurred over smaller spatial scales. Finally, the strength and direction of neighbourhood effects depended on neighbour traits and thus changed with the trait composition of the neighbourhood. 5. Synthesis. By manipulating both p
ISSN:0022-0477
1365-2745
DOI:10.1111/1365-2745.12816