Abstract
Understanding the timescales that shape spatial genetic structure is pivotal to ascertain the impact of habitat fragmentation on the genetic diversity and reproductive viability of long-lived plant populations. Combining genetic and ecological information with current and past fragmentation conditions allows the identification of the main drivers important in shaping population structure and declines in reproduction, which is crucial for informing conservation strategies. Using historic aerial photographs, we defined the past fragmentation conditions for the shrub Conospermum undulatum, a species now completely embedded in an urban area. We explored the impact of current and past conditions on its genetic layout and assessed the effects of genetic and environmental factors on its reproduction. The historically high structural connectivity was evident in the genetics of the species. Despite the current intense fragmentation, we found similar levels of genetic diversity across populations and a weak spatial genetic structure. Historical connectivity was negatively associated with genetic differentiation among populations and positively related to within-population genetic diversity. Variation partitioning of reproductive performance explained ~ 66% of the variance, showing significant influences for genetic (9%), environmental (15%), and combined (42%) fractions. Our study highlights the importance of considering the historical habitat dynamics when investigating fragmentation consequences in long-lived plants. A detailed characterization of fragmentation from 1953 has shown how low levels of genetic fixation are due to extensive gene flow through the non-fragmented landscape. Moreover, knowledge of the relationships between genetic and environmental variation and reproduction can help to implement effective conservation strategies, particularly in highly dynamic landscapes.
Highlights
Flowering plants are a crucial component of most terrestrial ecosystems (Ollerton et al 2006)
The generally even levels of genetic diversity and widespread presence of private genetic diversity reflects in the balanced percentage of individuals that should be collected from each population to maximise the allelic diversity
Genetic analysis of this threatened species revealed a relatively weak genetic structure and levels of genetic diversity and differentiation indices mainly influenced by historical levels of connectivity
Summary
Flowering plants are a crucial component of most terrestrial ecosystems (Ollerton et al 2006) They provide food and shelter for vertebrate and invertebrate populations, which in turn are important for plant pollination and seed dispersal. The structural changes imposed by anthropogenic habitat fragmentation can have a range of potentially deleterious genetic and demographic consequences (Haddad et al 2015). Such consequences may result from the loss of pollinators and other alterations to plant-pollinator interactions, as well as from the reduction of reproductive output due to drastic changes in the size and isolation of populations (Aguilar et al 2019; Lienert 2004; Potts et al 2010). Understanding the consequences of habitat fragmentation and the main drivers of declines in plant reproductive output is critical in implementing effective restoration strategies
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