Exchanging Genes Within a City: Analysis of Pollen Flow Patterns in a Narrow Endemic Plant Species Threatened by Urbanisation

Human-driven habitat fragmentation is known to disrupt gene flow in a wide range of species. However, its consequences for endemic plant species that depend on specialised invertebrate pollinators remain poorly understood. Although honeybees are capable of travelling considerable distances while foraging, many small-bodied native bee species lack the capacity to expand their foraging ranges or cross anthropogenic barriers, rendering habitat fragmentation the most significant threat to these ecological interactions. In many long-lived plants, the time since fragmentation has not been long enough for detectable changes in the genetic composition of standing populations. Changes in dispersal patterns observed in seedlings may thus provide insights into future impact of habitat changes. Using paternity assignment analysis, we characterised the plant mating system and changes in dispersal patterns across multiple fragmented and non-fragmented populations. Results showed that while pollen could travel unimpeded through unfragmented bushland, fragments separated by built-up areas resulted in complete isolation, with no pollen immigration. Extensive landscape fragmentation for urbanisation limited the capacity of native pollinators to maintain effective inter-population pollen flow. Reduced contemporary gene flow may limit the capacity of small populations to regain lost genetic diversity via connectivity with larger habitat remnants, potentially compromising the long-term persistence of threatened species that depend on specialised pollinators. These findings underscore the need to incorporate species-specific life history characteristics and ecological requirements into conservation planning, including translocation and reintroduction efforts, to ensure populations are large enough to maintain genetic diversity and functional mating systems within populations.