Effect of habitat fragmentation on seed dispersal ability of a wind-dispersed annual in an agroecosystem

Deficient dispersal ability due to habitat fragmentation adversely impact demographic connectivity and gene flow among population in a metapopulation, and therefore potentially leads to local extinction. A rich body of theoretical work provides distinct predictions regarding the distribution of dispersal abilities in relation to fragmentation gradient. Yet, empirical data remains elusive in general, and it is lacking for anthropogenic-induced landscapes in particular. We collected 9884 seeds of a wind-dispersed annual species Geropogon hybridus (Asteraceae) from 807 individual plants of 55 populations spanning three landscapes in a fragmented agroecosystem and measured four major dispersal-related traits at the landscape, population, plant and seed levels. Contrary to previous studies that were based on island or urban landscapes and where fragmentation was associated with reduced dispersal, we revealed increased seed dispersal ability in the more fragmented patches. However, the specific relationships between dispersal-related traits and fragmentation characteristics varied with ecological scale. The discrepancy between our results and those from previous studies may be explained by the milder contrast between the fragmented patches and the surrounding matrix in our system, which is a common feature in many agroecosystems. The findings add to the accumulating evidence that different selection pressures and constraints act on seed dispersal evolution under the global land use change.