Can a seed bank provide demographic and genetic rescue in a declining population of the endangered shrub Acacia pinguifolia?

Abstract

Many threatened species suffer reduced genetic diversity as a result of small population size and isolation. However, species with a persistent seed bank may be buffered against genetic loss as seed banks are expected to accumulate the reproductive output of many seasons. For fire-dependent species in decline, prescribed ecological burning may be a means to stimulate germination and recover genetic diversity stored in the seed bank, providing a demographic and genetic rescue effect. Here we investigated the effectiveness of this strategy in a small, isolated and inbred population of the endangered shrub, Acacia pinguifolia. We surveyed genetic diversity and structure of remnant populations of A. pinguifolia and monitored regeneration before and after burning. Germination was stimulated by fire, but seedling numbers 18 months postfire were low and barely above the number of adults killed by the fire. Genetic diversity was marginally higher in the post-fire seedling cohort than the pre-fire adults (H E = 0.1 vs. 0.09, respectively). Outcrossing rates of open-pollinated seed from surrounding plants suggested moderately high levels of self-fertilisation (t m = 0.65) and analysis of finescale genetic structure implied pollen and seed dispersal over distances of several metres, suggesting that restricted gene flow and inbreeding may act to limit genetic diversity in the seed bank. We conclude that prescribed burning has not been immediately successful as a recovery strategy for this relictual population of A. pinguifolia, though future monitoring may detect additional recruits. Alternative conservation strategies, including performing inter-population crosses, may be required to restore genetic diversity and ameliorate extinction risks.

Long-term nitrogen deposition depletes grassland seed banks

“…Such impoverishment threatens to increase the local extinction risk by reducing the capacity of the plant populations to recover from disturbance 9 . Loss of the seed bank also degrades a reservoir of genetic diversity 28 and therefore the ability of the community to respond to habitat alteration 29 and environmental change 30 . Finally, seed bank loss not only jeopardizes the natural ability of grasslands to recover from hazards such as fire, drought or overgrazing, but also limits the usefulness of seed banks as a source of plant material for the use in ecological restoration programmes.…”

Increased Genetic Diversity via Gene Flow Provides Hope for Acacia whibleyana, an Endangered Wattle Facing Extinction

“…The level of genetic structure found among A. whibleyena stands was high, given the small geographic range of the species (<38 km), and spatial location was a strong explanatory variable of the genetic variation in the species. The fact that the remaining A. whibleyana plants were distributed across small subpopulations suggests that genetic drift has played a part in shaping the genetic differentiation of the stands, as has been found for other endangered plant species, including the comparable Acacia pinguifolia [36]. Acacias are mostly pollinated by generalists, with bees their most common pollinators [37].…”

“…Similar patterns were also observed for A. pinguifolia, which is another threatened species endemic to a similar region to A. whibleyana. A. pinguifolia presented high levels of historical inbreeding, strong fine-scale genetic structure, and limited inter-stand gene flow [36]. Crossing between populations was recommended as a strategy to help reduce the risk of extinction in this species [36].…”

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

“…Small or fluctuating population size; seed bank is small and/or established from genetically depauperate population (Evans et al ., ; Ottewell et al ., )…”