Spatio-temporal variability in plant reproduction across a fragmented landscape of Southern Australia

Author: Alex Blackall

Blackall, Alex, 2023 Spatio-temporal variability in plant reproduction across a fragmented landscape of Southern Australia, Flinders University, College of Science and Engineering

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The research in this thesis explores spatio-temporal variability in pollination and reproduction of three plant species with contrasting pollination systems across a range of reserve areas protecting plant populations within a fragmented landscape of southern Australia. In particular, plants were chosen with ecological traits that have not usually been displayed by plants included in previous studies of landscape disturbance. Thus, this research examined three common species rather than the rare and threatened species which are more typically studied. This research also included the study of a plant species with high levels of insect pre-dispersal seed predation, which is an understudied biotic interaction in fragmented landscapes, and finally this research included a nocturnally moth-pollinated species whereas most studies have focused on plants with diurnal rather than nocturnal pollinators.

There was no evidence of pollen-limitation of reproduction of the papilionaceous legume Pultenaea daphnoides J.C.Wendl. (Chapter Two) in the two years studied. This may have been due to the relative diversity of bee visitors to flowers of P. daphnoides, including the introduced honeybee, Apis mellifera. However, viable seed production was mostly limited to the smallest reserves assessed in 2018, with almost complete abortion of viable seeds in larger reserves. This striking result occurred in a year of historically low early spring rainfall and highlights the possibility that smaller reserves may maintain at least some viable seed production across fragmented landscapes in particular years. However, plants within both small and large reserves were both successful at producing viable seeds in the previous year of 2017, and thus reserve area was not a consistent predictor of reproductive success.

In contrast to P. daphnoides, fruit production of the relatively more specialized buzz-pollinated Hibbertia exutiacies N.A.Wakef. (Chapter Three) was significantly pollen-limited in 2017, perhaps suggesting the more specialized pollination system of H. exutiacies increases the risk of reproductive failure. Viable seed production in 2017 was also positively related to the amount of native vegetation in the landscape surrounding sample sites, which was not necessarily related to reserve area, and this positive relationship appeared to be largely due to spatial variation in this species’ high level of insect pre-dispersal seed predation. However, similar to P. daphnoides, H. exutiacies displayed almost complete abortion of seed development in the following year of 2018. An experimental field study of two populations in 2019 demonstrated that water stress may limit reproduction in particular years for some populations (Chapter Four).

In comparison to H. exutiacies and P. daphnoides, reproduction of the nocturnally moth-pollinated Stackhousia aspericocca Schuch. ssp. Cylindrical inflorescence (W.R.Barker 1418) W.R.Barker (Chapter Five) was comparable between smaller and larger reserves in 2018 and 2019 and there was no significant difference in reproduction between years.

Regarding the conservation of common plants within fragmented landscapes, the findings of this thesis do not suggest the studied plant species are at greater risk of reproductive failure within smaller reserves versus larger reserves. Nevertheless, the idiosyncratic responses of the three species studied emphasises the importance of continued empirical studies of pollination and plant reproduction within fragmented landscapes.

Keywords: habitat loss, fragmentation, landscape disturbance, reserve area, scale-of-effect, plant reproduction, fruit-set, seed-set, pollen-limitation, water-limitation, rainfall, climate change, pre-dispersal seed predation, buzz-pollination, sonication, moth pollination, Fabaceae, Leguminosae, Mirbelieae, Pultenaea daphnoides, Dilleniaceae, Hibbertia exutiacies, Celastraceae, Stackhousia aspericocca, common plant species, sclerophyllous, South Australia, Mount Lofty Ranges, plant conservation, temporal variability

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Science and Engineering
Supervisor: Duncan Mackay