Large seeds, extinct vectors and contemporary ecology: testing dispersal in a locally distributed cycad, Macrozamia lucida (Cycadales)

Abstract

The possible reasons for the localised distribution of Macrozamia lucida Johnson in south-eastern Queensland were investigated through testing and quantifying aspects of seed dispersal, ex situ germination across local substrates and the spatial distribution of plants of different ages. Seeds of cones exposed to animals were moved significantly further (108.4 ± 13 cm, n = 10 cones) than those of cones not exposed to animals (49 ± 11 cm, n = 4). Only two mammal species interacted with seeds, common brushtail possums (Trichosurus vulpecula) and bush rats (Rattus fuscipes), but relatively infrequently. The possums were both seed dispersers and predators, whereas the rats ate only sarcotesta. Seed predation and removal occurred at a constant but low rate at cones exposed to animals, compared with no seed removal at unexposed cones. Seeds with sarcotesta intact and sarcotesta alone suffered significantly higher rates of removal by mammals. Seeds in soil had a significantly higher rate of germination (50%) than those in gravel (24.4%) or leaf litter (25.6%) and partially buried seeds germinated at a significantly higher rate (51.2%) than those on the surface (23.2%) and those buried completely (25.6%). In summary, this population appears to be localised spatially by low rates of dispersal, restricted dispersal distance and limited sites for successful germination. The results are discussed in relation to the possible extinction of the original seed dispersers of these organisms and the limitations this imposes on these plants should they be exposed to an unfavourable climatic regime.

Anything more than a picnic? Re‐considering arguments for ceremonial Macrozamia use in mid‐Holocene Australia

“…While there are significant rates of rodent toothmarking on the sclerotesta in some levels of the sites (discussed further below), the rate at which seeds were gnawed open is consistent with rates of gnawing observed on seeds found at the base of parent plants (Burbidge and Whelan 1982;Jones 1987;Snow and Walter 2007). Given the vast majority of seeds showed the direct evidence of human processing and very few seeds were gnawed open (less than 1% at each site), it is likely that gnawing of seeds had taken place prior to collection by human foragers.…”

Geographical variation in cone volatile composition among populations of the African cycad Encephalartos villosus

“…Long distance dispersal of seeds from the southern part of the range is highly unlikely to account for the volatile components of the VCNR population. There is no known long distance dispersal mechanism and cycad dispersal is typically within a short distance of the parent plant (Snow & Walter, 2007). Long range pollen dispersal (> 5 km) also appears to be unlikely because Donaldson (1997) discovered that Porthetes sp., Erotylidae sp.…”

Historia natural de Dioon Merolae (Zamiaceae)en Chiapas, México

“…En la mayor extensión del área de distribución de D. merolae se ha presentado en el último siglo un severo proceso de defaunación que ha ocasionado la casi extinción regional o alteración severa de las poblaciones de mamíferos de tamaño medio o grande como el venado cola blanca Odocoileus virginianus Zimmermann, los pecaríes Pecari tajacu Linnaeus y Tayassu pecari Link (Naranjo et al, 2005) y cánidos y mustélidos que podrían mover las semillas con sarcotesta. Finalmente, el tamaño de las semillas puede asociarse con megafauna extinta que pudo realizar su dispersión por endozoocoria (Janzen y Martin, 1982;Janzen, 1986), como también se ha sugerido para M. lucida (Snow y Walter, 2007). La antigüedad de las Cycadales sugiere que en otros periodos pudieron mantenerse prolongadas interacciones con dispersores ahora extintos, como se ha sugerido para un amplio conjunto de especies vegetales neotropicales que mantienen aparentes anacronismos ecológicos entre sus frutos y las poblaciones de animales que podrían dispersarlos (Janzen y Martin, 1982;Janzen, 1986;Barlow, 2000).…”