Patchy distribution and varied habitats of Macrozamia lucida cycads explained by constancy in a key environmental variable

Abstract

Identifying the influence of environmental variables on the spatio-temporal distribution of organisms remains a central goal of ecology. Although environmental limits to the geographic range of species have been investigated, less information is available regarding the influence of environmental variables limiting species to discrete patches within their geographic range. Identifying environmental variables of importance to the species in question is further complicated where the patches appear to be distributed across a variety of outwardly dissimilar habitats. We assessed the influence of environmental variables on the patchy distribution of Macrozamia lucida L.A.S. Johnson (Zamiaceae) cycads endemic to south-east Queensland, Australia. Here we show that patches of M. lucida are consistently associated with elevated moisture, despite the patches being located in contrasting habitats and topographic positions. Our survey results across five field sites demonstrate that both cycad abundance and adult cycad condition (estimated from measures of adult cycad leaf production and reproductive output) are positively correlated with elevated moisture, as measured by mean minimum relative humidity at the plant–soil interface. The historical biogeography of the genus Macrozamia may be intimately linked with the contraction and fragmentation of Australia’s mesic biomes during the Miocene. It is plausible that current distribution pattern of M. lucida, restricted to discrete patches that meet the species’ environmental requirements, reflects a contraction and fragmentation within its range from a more regular historical distribution under more favourable climatic regimes.

Different Criteria for Evaluation of the Conservation Status of Ceratozamia Miqueliana (Zamiaceae)

“…Humidity is the factor most related to the presence of the plant. A similar result was reported by Kaye et al (2016) for Macrozamia lucida, a species that inhabits Australia; while maximum temperature has been reported as such for Macrozamia macdonnellii (Preece et al, 2007).…”

“…The results of the Maxent model indicate that C. miqueliana requires specific environmental conditions, such as those of the soil (in this case, an acrisol), which was also found to be one of the most important variables in terms of conservation of this group of plants. Soil is the most important variable for some cycads, such as Encephalartos latifrons (Swart et al., 2018), Dioon sonorense (Álvarez-Yépiz et al., 2011), Macrozamia macdonnellii (Preece et al., 2007) and Macrozamia lucida , a species for which the soil is the most important variable in terms of abundance (Kaye et al., 2016). The presence of high concentrations of potassium characterizes the acrisol soil type, which is associated with humid tropical zones with tropical rain forest (TRF) vegetation that facilitates a greater retention of moisture on the leaves of the plants (Food and Agriculture Organization, 2008).…”

The interaction between diet breadth, geography and gene flow in herbivorous insects

“…obs.). It may be that suitable environmental conditions for these cycads (Kaye et al 2016) are rare in this area, and so their distribution has become restricted over time due to climactic change. These factors will need to be investigated specifically in future.…”

“…These cycads overlap geographically and do produce hybrids in at least one locality where they overlap (Terry et al 2004). Both species have a patchy distribution, and in M. lucida this is known to reflect its specific environmental requirements (Kaye et al 2016). That means that the fragmented spatial distribution of Macrozamia is likely to influence the genetic structure of this thrips species, spatially and temporally.…”