Plant isolation reduces outcross pollen receipt in a partially self‐compatible herb

Abstract

Summary1 Few studies of pollination success in fragmented systems measure stigmatic pollen load, and those that do often find it unrelated to plant or population density, size or isolation. Reduced reproductive output, however, is commonly reported, probably because incompatible pollen is contributing substantially to pollen loads of isolated flowers. 2 We used manipulated floral arrays of a bee-pollinated species ( Dianella revoluta ) to investigate isolation effects on deposition of outcross pollen, while precluding self-pollen transfer. 3 Outcross pollen receipt declined significantly over short distances up to approximately 50 m but even the most isolated flowers received some pollen grains. In contrast, heterospecific pollen did not decline, indicating that the outcross-pollen decline was not due to reduced pollinator visitation. Increased distance of experimental arrays from a nature reserve did not reduce the probability of pollen receipt. 4 Many flowers were damaged by flower feeding beetles in the genus Arsipoda , which would be likely to substantially reduce the efficiency with which flowers are converted to fruits. The probability of flower damage from these predators was significantly lower in arrays that were more distant from the nature reserve. 5 This study indicates that reduced plant density and increased isolation from a source of outcrossed pollen can lead to a substantial decline in the probability of outcrossing, even when pollinator visitation is maintained at a high level. Depending on the mating system, this process will lead to reduced seed set or increased inbreeding for plants in fragmented habitats, even when pollinator abundance and behaviour are unaffected.

Delayed response in a plant–pollinator system to experimental grassland fragmentation

“…Duncan et al 2004;Ward and Johnson 2005). Pollinator limitation may not occur when the pollinators are able to Xy long distances.…”

Relationships between the floral neighborhood and individual pollen limitation in two self-incompatible herbs

“…All of these studies found negative relationships between conspeciWc Xower density (measured either as conspeciWc density or as isolation of target individuals) and individual pollen limitation. Several within-population studies have associated conspeciWc Xower density with other variables that are related to pollen limitation, such as seed/ fruit production (Roll et al 1997;Somanathan and Borges 2004;Pettersson 1997;Spigler and Chang 2008), pollen deposition and/or removal (Johnson et al 2003;Duncan et al 2004), stigma persistence (Wagenius et al 2007), or seed/ fruit production in combination with pollinator visits and/or pollen deposition (Aizen 1997;Waser 1999, 2001;Caruso 1999;Caruso 2002;Kirchner et al 2005).…”

Disentangling multiple drivers of pollination in a landscape-scale experiment

“…isolation of the plant population), through lowered pollinator density (caused by isolation of pollinator habitat) and through changes in pollinator movement [12]. Isolated plant populations can show lower pollination success independent of pollinator visitation because of a lack of compatible donor plants [18]. In turn, the absence of pollinators can decrease pollination success even in situations where the availability of donor plants is high [15].…”