The role of fire and a long‐lived soil seed bank in maintaining persistence, genetic diversity and connectivity in a fire‐prone landscape

Abstract

Aim Terrestrial plant ecology and evolution is significantly influenced by the phenomenon of fire, but studies of its potential impact on intraspecific genetic variation and phylogeography are rare. This understanding will be important for predicting the biogeographical consequences of changing fire regimes under global climate change. Here, we asked whether changing historical fire regimes, together with climatic and geological history, have influenced phylogeographical patterns in a fire-ephemeral vine. We also asked whether demographic stochasticity associated with a fire-ephemeral life history results in nuclear genetic drift as expected from spatio-temporal patchiness, or if this effect is buffered by the connectivity and diversity afforded by a persistent soil seed bank.Location The fire-prone, mediterranean-type climate region of south-western Australia.Methods We used Bayesian phylogeny reconstruction and statistical tests of demographic expansion based on variation at three non-coding chloroplast sequence regions (atpF, ndhF-rpl32, psbD-trnT) to reconstruct phylogeographical history. Nuclear diversity and population structure at 11 microsatellite loci were investigated for evidence of genetic drift.Results Evidence for prolonged persistence and a lack of vicariance within the species range was found, together with strong evidence of historical demographic expansion. Contrary to expectations, there was little evidence of nuclear genetic drift despite strong, above-ground spatio-temporal population patchiness.Main conclusions Our findings suggest that a late Pleistocene increase in fire frequency may have led to demographic expansion in this fire-ephemeral species; alternatively, the expansion signal may be an inherent feature of fire ephemerals with a persistent soil seed bank. Prolonged climatic stability has likely fostered persistence within the species range in contrast to contraction and vicariance. The notable lack of genetic drift implies a role for ample pollen dispersal and a long-lived soil seed bank in the maintenance of diversity and connectivity in an otherwise stochastic, fire-driven system.

How does the post‐fire facultative seeding strategy impact genetic variation and phylogeographical history? The case of Bossiaea ornata (Fabaceae) in a fire‐prone, mediterranean‐climate ecosystem

“…As predicted, a very high level of genetic diversity was evident within and among populations of B. ornata , in both the nuclear and chloroplast genomes. Microsatellite diversity levels were consistently high within all sampled populations, and mean values of heterozygosity were higher than observed for other widespread (Ritchie & Krauss, ; Bradbury et al ., , ) and restricted species (Sampson et al ., ; Menz et al ., ) in the mesic SWAFR. The number of chloroplast haplotypes observed was also remarkable, being extremely high in comparison to other species both globally (reviewed by Petit et al ., ) and widespread within the SWAFR using similar molecular markers (Nistelberger et al ., ; Bradbury et al ., ).…”

“…Investigations of evolutionary drivers among resprouter and seeder fire‐response strategies at the genus and community level (macroevolutionary processes) in fire‐prone MCEs have suggested that resprouting is an ancestral plant state that has provided resilience to many kinds of disturbances including fire, drought, grazing and frost (Wells, ; Pausas & Keeley, ), while facultative seeding is hypothesized to be derived from obligate resprouting, which in turn probably facilitated the evolution of obligate seeding in regions where fire is a reliable and regular disturbance (Pausas & Keeley, ). In contrast, studies that investigate the drivers and distribution of genetic diversity on microevolutionary scales among populations of resprouting and seeding species, are rare (Premoli & Kitzberger, ; Premoli & Steinke, ; Segarra‐Moragues & Ojeda, ; Segarra‐Moragues et al ., ), especially those that concurrently investigate phylogeographical history (Bradbury et al ., ). Such studies inform intraspecific diversification processes, a fundamental basis for broader macroevolutionary processes.…”

“…Diversity harboured or accumulated in large and/or long‐lived seed bank (Honnay et al ., ; Bradbury et al ., )…”

“…Populations established/supplemented by multiple seedling recruits from a diverse soil seed bank (Ayre et al ., ; Banks et al ., ; Bradbury et al ., )…”

Severe effects of long-term drought on calcareous grassland seed banks

“…We expect our results to enhance our understanding of the effects of climate change on ecosystems. Seed banks represent biodiversity reservoirs for grasslands and other ecosystems on a global scale, 31 playing an important role in the maintenance of genetic and species diversity, 32,33 and in the reestablishment of species lost from the above-ground vegetation. 34 Moreover, they reduce the risk of extinction as a consequence of a single environmental event such as drought or flooding.…”