Stepping-stone populations in linear landscape elements increase pollen dispersal between urban forest fragments

Abstract

Background and aims -Understanding how to ensure connectivity by gene flow between insect-pollinated plant populations is essential for designing functional ecological networks in a human-dominated matrix such as in urban settings. Linear landscape elements (LLEs) might contribute to such connectivity by increasing pollen transfer. Methods -Pollen dispersal was investigated for the insect-pollinated herb Primula elatior in urban forest remnants, using fluorescent dye as a pollen analogue, in three study sites comprising population pairs located in fragments connected or not by a wooded LLE. We examined whether the presence of a small patch of plants of P. elatior placed within the LLE (stepping-stone population) might increase pollen dispersal compared to an LLE where P. elatior is absent. Key results -Dye dispersal showed a leptokurtic decay distribution, with most dye transfer events at short distances (80% at less than 15.4-114.8 m) and a maximal distance of 647.5 m. Populations not connected by an LLE, separated by distances of 249 m or more, did not exchange dye, whereas populations that were connected by LLEs (up to 602 m) did show interpopulation dye transfer, suggesting that LLEs function as biological corridors facilitating dye dispersal. The presence of a stepping-stone population of P. elatior within the LLE increased between-population dye transfers (between 1.8 and 3.3 times the proportion of visited individuals) and deposition distances, compared to an LLE with no stepping stone, at least when pollen flow already existed. Conclusions -These results provide evidence that LLEs may be more effective for pollen dispersal when serving as both movement conduit and habitat. In urban settings, developing a network of core populations connected by LLEs comprising small, even temporary, stepping-stone populations should be encouraged.

What influences pollen dispersal in the clonal distylous Menyanthes trifoliata (Menyanthaceae)?

“…Similar distance ranges of within-population dye or pollen deposition were found for other bee-pollinated plant species (Kwak et al 1998), e.g. for the distylous Primula elatior , Van Rossum & Triest 2012 and Vaccinium oxycoccos (Van Rossum et al 2013). However, even if fluorescent dye usually provides a reliable analogue for pollen movement, especially by bees (Waser 1988, Dudash 1991, Rademaker et al 1997, mirroring pollinator activity (Mayer et al 2012b), dye particles may be smaller and less sticky than pollen grains and may be transported less far or farther than pollen and/or in different amounts, and may under-or overestimate pollen dispersal (Thomson et al 1986, Campbell 1991, Adler & Irwin 2006, so that whether dye dispersal accurately reflects pollen dispersal in M. trifoliata still needs to be verified.…”

“…In both regions, fen and bog populations appear isolated from each other, suggesting that restoring connectivity through extending habitat surface (e.g. fen and bog restoration after cutting of spruce plantation), biological corridors or stepping-stone populations might be needed (Van Geert et al 2010, Van Rossum & Triest 2012. Pollen dispersal may also be shaped by the interaction between population traits (e.g.…”

The structural and functional connectivity of the grassland plant Lychnis flos-cuculi

“…Recent studies have demonstrated that open areas in European agricultural landscapes do in fact enhance pollen flow among spatially isolated insect-pollinated plants (Kamm et al, 2010). Furthermore, agricultural areas with a network of structurally connected seminatural linear elements still contain small stepping-stone plant populations that support higher levels of gene flow (Van Geert et al, 2010;Van Rossum and Triest, 2012). In our study area, field boundaries adjacent to roads or forests were the most common seminatural habitats and could have mitigated the potential negative effect of agricultural fields on gene flow in L. flos-cuculi, at least to a certain extent.…”

Ditch network sustains functional connectivity and influences patterns of gene flow in an intensive agricultural landscape

“…As semi-natural linear pathways within the agricultural matrix, native and introduced vegetation occurring on ditch banks may enhance pollinators' movements among habitat patches, as shown for other linear landscape elements (Cranmer et al, 2012;Van Rossum and Triest, 2012). In addition, water flow is also expected to facilitate seed dispersal.…”