The distribution of dioecious plant pollination, sex ratio and seed dispersal research by climate type in Australia

Abstract

Dioecious-plant life-history characteristics and reproduction vary greatly among species, and have been linked to certain climate and habitat types, particularly tropical and island habitats. Australia is a large, predominantly arid continent, although it also contains mediterranean, temperate and tropical climates. Dioecious plants occupy each of these climate types, with their respective habitats and evolutionary pressures. As a result, dioecious species demonstrate great variation in key reproductive characteristics (pollination mechanism, sex ratio, and seed dispersal), which require understanding so as to conserve dioecious species effectively among climate types. Therefore, to understand dioecious-plant ecology across Australia, research must include all climate types, and investigate reproductive traits in each to better focus conservation strategies. An external factor which could prevent equal study effort across climate types would be geoclimatic preference of study location or biases in researcher interest, causing gaps in practical understanding and less effective dioecious-plant conservation management in understudied systems. To assess the prevalence and nature of dioecious plant research in Australia, we conducted a systematic mapping and scoping review to answer the following questions: (1) what climate zones have been captured by dioecious-plant research in Australia, focusing on pollination, sex ratio and seed dispersal; and (2) what is the distribution of dioecious-plant pollination, sex ratio and seed dispersal research by climate type; of the 43 studies that met the inclusion criteria, 27 (62.8%) studies were conducted in temperate climates, 8 (18.6%) in dry climates, 6 (13.9%) in tropical climates, and 5 (11.6%) in continental climates. Of the three focal areas, pollination studies (n = 24, 75% studies of entomophily) were most common, whereas sex ratio (n = 17, 41% studies of sex ratio over more than one population) and seed dispersal studies (n = 13, 54% of studies investigated abiotic dispersal) were less frequently researched. Considering the climate classification distribution in Australia, studies of dioecious species in dry climates are less prevalent than those in temperate climates. Of the focal areas of research, particularly under-investigated areas were anemophily, biotic seed dispersal, and study of female-biased species. Further studies addressing these gaps would be beneficial to inform conservation initiatives for Australian dioecious plant species. Additionally, it would be informative to investigate whether similar patterns are found in dioecious plant research in other countries with diverse climate types.