Disturbance‐induced density‐dependent seed set in Shorea siamensis (Dipterocarpaceae), a tropical forest tree

Abstract

Summary 0The reproductive output of Shorea siamensis\ a widespread dipterocarp tree\ was assessed in relation to disturbance and tree density at three sites in western Thailand during the 0885 and 0886~owering seasons[ The locations were similar except in disturbance history\ which was re~ected in decreasing tree density from undisturbed via moderately disturbed to disturbed sites[ 1 Hand pollination experiments showed S[ siamensis to be partially self!incompatible due to di}erential pollen tube growth and abortion of inbred fruit[ Although more than 89) of~owers from trees at all sites were pollinated\ pollen tubes developed in only a small proportion of these~owers[ Both pollen tube development and initial fruit production were highest at the undisturbed site[ Many fruit\ presumably selfed\ were aborted during development at all sites\ but signi_cantly more fruit were aborted at the disturbed site\ resulting in lowered production of mature fruit[ 2 Shorea siamensis was pollinated by small Tri`ona bees\ which exhibited signi_cant declines in intertree movements with increasing distance between~owering trees[ As resource availability did not di}er between sites\ di}erences in mature fruit set were considered to be mediated by changes in pollinator foraging behaviour at di}ering tree densities[ Variation in seed set was found to be negatively correlated with distance to nearest conspeci_c both within and between sites[ 3 At the two least disturbed sites observed seed set values corresponded with those expected by calculation[ However\ seed set at the disturbed site was signi_cantly lower than expected[ 4 Our results suggest that high reproductive success of S[ siamensis is dependent upon cross!pollination which\ through pollinator behaviour\ is a function of tree isolation[ This species may thus be subject to the Allee e}ect\ where population viability is reduced disproportionately with a decline in population size or\ as in this study\ population density[ The implications of these results for population recovery and genetic structure following disturbance are discussed[ Keywords] Allee e}ect\ disturbance\ forest regeneration\ gene~ow\ outcrossing\ pol! lination\ population viability Journal of Ecology "0887# 75\ 351Ð362

Reduced density due to logging and its consequences on mating system and pollen flow in the African mahogany Entandrophragma cylindricum

“…In some species, lower densities not only result in selfing, higher inbreeding and genetic relatedness within progenies (e.g., Murawski and Hamrick, 1991, for nine species under natural conditions; Lee et al, 2000;Obayashi et al, 2002), but also lowered fecundity (Ghazoul et al, 1998;Cunningham, 2000). Other species seem to be largely unaffected by low population densities (e.g., Kitamura et al, 1994;Hall et al, 1996).…”

Effects of local conspecific abundance on seed set and seed predation, and control of Carpinus laxiflora (Betulaceae) population density

“…However, local abundance was measured within a radius of 80 m in both studies, and whether the most effective distance is larger remains unknown. Pollen limitation has also been reported for insect-pollinated plants (Silander 1978, House 1993, Ghazoul et al 1998, García and Chacoff 2007, Dauber et al 2010, Jakobsson and Ågren 2014. Among basal areas of target individuals did not have significant effects in most situations (Table 1).…”

“…Previous studies have shown that pollination efficiency is positively correlated with local conspecific density of reproductive individuals. Moreover, multiple insect-pollinated plants are subjected to a decreased attraction of pollinators following fragmentation or isolation of the population (Silander 1978, House 1993, Ghazoul et al 1998, García and Chacoff 2007 April in this area, and fruit ripens in September-October. Seeds develop to full size even in unfertilized female flowers, and most remain on inflorescences until the main season of dispersal by wind (Shibata 2006).…”

Genetic structure and genetic diversity of <em>Swietenia macrophylla</em> in areas subjected to selective logging in Quintana Roo, Mexico

“…First, changes in behaviour of pollinators affecting reproductive success in tropical trees have been detected in disturbed forests (Ghazoul et al, 1998;Ghazoul and McLeish, 2001). Second, outcrossing rates may be also diminished by a reduction in the proportion of fl owering trees in logged forests (Murawski and Hamrick, 1991;Murawski et al, 1994;Obayashi et al, 2002).…”