Waterfowl endozoochory: An overlooked long-distance dispersal mode forCuscuta(dodder)

Several plant traits are known to evolve in predictable ways on islands. For example, herbaceous species often evolve to become woody and species frequently evolve larger leaves, regardless of growth form. However, our understanding of how seed sizes might evolve on islands lags far behind other plant traits. Here, we conduct the first test for macroevolutionary patterns of seed size on islands. We tested for differences in seed size between 40 island–mainland taxonomic pairings from four island groups surrounding New Zealand. Seed size data were collected in the field and then augmented by published seed descriptions to produce a more comprehensive dataset. Seed sizes of insular plants were consistently larger than mainland relatives, even after accounting for differences in growth form, dispersal mode and evolutionary history. Selection may favour seed size increases on islands to reduce dispersibility, as long-distance dispersal may result in propagule mortality at sea. Alternatively, larger seeds tend to generate larger seedlings, which are more likely to establish and outcompete neighbours. Our results indicate there is a general tendency for the evolution of large seeds on islands, but the mechanisms responsible for this evolutionary pathway have yet to be fully resolved.

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Dispersal traits in the hyper-arid hot desert of the United Arab Emirates

Plant Ecology and Evolution ◽

10.5091/plecevo.2018.1359 ◽

2018 ◽

Vol 151 (2) ◽

pp. 194-208 ◽

Cited By ~ 3

Author(s):

Hatem A. Shabana ◽

Teresa Navarro ◽

Ali El-Keblawy

Keyword(s):

United Arab Emirates ◽

Dry Season ◽

Arid Environments ◽

Long Distance Dispersal ◽

Species Dispersal ◽

Long Distance ◽

Dispersal Mode ◽

Dispersal Traits ◽

Floristic Elements ◽

Soil Cracks

Background and aims – This study describes the dispersal traits of 302 species in five Afro-Arabian habitats from the hyper-arid hot desert of United Arabian Emirates (UAE).Methods – Diaspore size (diaspora length) was studied in relation to growth forms, dispersal modes, presence of structures for long distance dispersal, APG IV groups, phytogeography and dispersal phenology using ANOVA and Pearson χ2 test-statistical analyses.Results – Small diaspores were predominant (six orders of magnitude from 10-4 to 102). The major diaspores were found in Fabids phylogenetic APG IV group (1.80±0.41 cm) mainly trees and the minor in Commelinids (0.30±0.08 cm). The most dominant dispersal mode was semachory (43.7% of the total and 67.5% of the herbaceous species), followed by anemo-meteochory (28.8%) and barochory (23.8%). Semachores/barochores (67.5%) formed the largest groups from the Fabaceae, Poaceae, Boraginaceae, Brassicaceae and Amaranthaceae families. Savanna trees such as Acacia, Prosopis, Ziziphus sp. and Indigofera sp. produced large diaspores secondarily dispersed by vertebrates. Anemo-meteochoric species with small diaspores were predominantly semi-shrubs such as Haloxylon sp. Graminoids such as Stipa sp. and Stipagrostis sp., without structures for long-distance dispersal had diaspore appendages acted as “active drills” in soil cracks. Dryness (dry season) favours the efficient dispersion by the wind for the small shrub species with haired capsule (e.g. Aerva javanica), winged calyx (e.g. Astragalus squarrosus) or wings (e.g. Tribulus qatarensis). Most of the species studied (64.2%) dispersed in the dry season according to what was found in other arid region from the world. The longer dispersal phenology corresponded to Saharo-Arabian and Sudano-Decanian species which is related to the floristic richness of the study area. Species dispersal throughout the year indicates an important seed resource e.g. barochoric species with fleshy fruits or pods with nutrient structures (e.g. Senna italica and Indigofera sp.).Conclusions – In the hyper-arid hot desert of UAE, the dispersal spectra are close to those recorded in other arid environments but with particularities due to the presence of African floristic elements.

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