Abstract
Clonal species normally have low seed production, low recruitment rates and long lifespans, and it is expected that the rates of long-distance dispersal (LDD) of seeds will be low as well. Banksia candolleana is a clonal shrub in Mediterranean-type, fire-prone sclerophyll shrublands of southwestern Australia, whose reproductive biology and population dynamics contrast with those of co-occurring nonclonal congeneric species, all of which are restricted to a mosaic of sand dunes set within a matrix of inhospitable swales. Using microsatellite markers, we genotyped 499 plants in all 15 populations of B. candolleana within a 12-km2 area, assessed population genetic differentiation, and quantified the effective rate of interpopulation seed dispersal through genetic assignment of individuals to populations. We measured life history, reproductive and demographic attributes, and compared these with two co-occurring Banksia species, a non-clonal resprouter and a nonsprouter. B. candolleana has much higher levels of population genetic differentiation, and one-third the rate of interpopulation seed migration, as the other two species (2.2% vs 5.5−6.8% of genotyped plants inferred to be immigrants), though distances reached by LDD are comparable (0.3−2.3 km). The low rate of interpopulation dispersal was supported by an analysis of the age structure of three populations that suggests a mean interdune migration rate of <800 m in 200 years, and 60% of suitable dunes remain uninhabited. Thus, B. candolleana has poor properties for promoting long-distance dispersal. It is unclear if these are idiosyncratic to this species or whether such properties are to be expected of clonal species in general where LDD is less critical for species survival.
Highlights
Landscape genetics addresses how landscape elements, environmental factors and species life-histories influence the process and pattern of genetic connectivity and the spatial distribution of genetic variation within and among populations [1], [2], [3]
B. candolleana has poor properties for promoting long-distance dispersal. It is unclear if these are idiosyncratic to this species or whether such properties are to be expected of clonal species in general where LDD is less critical for species survival
Collating data we have on pollinators and relative pollen production and transport (Table 5), interpopulation pollen flow is expected to be only marginally less successful for B. candolleana than for B. attenuata, with both far less efficient than B. hookeriana, a highly successful bird-pollinated species that has strong evidence of interpopulation pollen flow [25], [48]
Summary
Landscape genetics addresses how landscape elements, environmental factors and species life-histories influence the process and pattern of genetic connectivity and the spatial distribution of genetic variation within and among populations [1], [2], [3]. Genetic connectivity among plant populations is achieved through the movement of pollen and seeds, but especially through the dynamics of seed dispersal [4], [5]. Most seeds are dispersed within the vicinity of the maternal plant, but long-distance dispersal (LDD) vectors may take seeds into new habitats or different populations. Though rare, these events are disproportionally important for species dynamics at the landscape scale [4], [6]. LDD of seeds, defined by Nathan et al [7] as dispersal to a distance at least 100 times plant height, plays a crucial role in metapopulation dynamics through colonisation of new habitats and/or recolonisation following local extinction [8]. Dispersal may be considered a bet-hedging strategy, allowing metapopulation persistence when any single habitat patch is only transiently favorable [9]
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