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Mackay, Keith David
- PublicationClimate Change Threatens a Fig-Frugivore Mutualism at its Drier, Western Range MarginFicus rubiginosa (the Rusty Fig; Moraceae) provides a keystone food resource for a diverse array of vertebrate frugivores in eastern Australia. These frugivores, in turn, provide vital seed-dispersal services to the fig. The aims of this study were to investigate impacts of population size and climatic variation on avian-frugivore visitation to F. rubiginosa at the extreme western, drier margin of the species' range. Eighty-two bird species visited F. rubiginosa trees in this three-year study. Twenty-nine species were frugivores or omnivorous frugivore/insectivores. The number of ripe fruit in a tree had the greatest positive influence on frugivore visitation (p < 0.0001). Fig-population size influenced the assemblage of frugivore species visiting trees but not the number of frugivores or the rate of frugivore visitation. The number of ripe fruit in a tree was negatively associated with declines in rainfall, to total losses of standing crops through dieback and lack of crop initiation. Predicted long-term declines in rainfall across this region of eastern Australia and increased incidence of drought will lead to reduced crop sizes in F. rubiginosa and likely reduce the viability of local populations of this keystone fig. This will threaten the mutualism between F. rubiginosa and frugivores across the region.
- PublicationUnsuccessful introduced biocontrol agents can act as pollinators of invasive weeds: Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) as an example(2017-08-22)
- PublicationSmall populations of fig trees offer a keystone food resource and conservation benefits for declining insectivorous birdsNovel restoration approaches are required to provide food and habitat for declining bird populations, particularly as pressures increase from growing human populations and climate change. Fig (Ficus) species support many frugivores but there is a gap in our knowledge about the importance of these insect-pollinated plants to insectivores. We tested the influences of fig-population size and the number of fig-wasp-producing fruit per tree on avian-insectivore visitation to fig trees in eastern Australia over a three-year period. Eighty-four bird species visited fig trees in our study; two thirds (55) of these species were insectivores. More individual insectivores (1686) than frugivores (1051) visited fig trees (p < 0.0001). More insectivore species visited individual fig trees in small, fragmented populations (<16 fig trees) than in large populations (>50 fig trees; p = 0.016). We showed that figs provide insectivores with an important, year-round, food source. We showed that this occurred in a dry, temperate ecosystem and in a mesic, sub-tropical ecosystem. Insectivore visitation was significantly correlated with the number of ripening fig syconia and the number of emerging fig wasps but not with abundances of other insects in fig trees. Temporal resource partitioning between insectivores and frugivores was identified, with insectivores foraging as fig syconia were ripening, and frugivores foraging after syconia had fully ripened. Ficus species are very likely to provide similar keystone resources for avian insectivores throughout tropical, subtropical and temperate regions globally. This study revises our understanding of the role played by Ficus trees in supporting avian-insectivore populations.
- PublicationFicus rubiginosa, fruitset data and wasp and seed dataAim: We tested four hypotheses: (1) that pioneer trees at distribution margins would receive fewer visits from pollinators and pollinator parasitoids than would trees in larger, established populations; (2) that predator release (lower rates of pollinator parasitism) would result in higher pollinator reproductive success; (3) that less competition among fewer pollinator foundresses would correlate with higher plant reproductive success; and (4) that these effects would be greater at the plant species’ expanding range margin. Location: The dry, western side of the Great Dividing Range in northern New South Wales, eastern Australia. Taxon: The rusty fig (Ficus rubiginosa, Moraceae), its pollinator and the pollinator’s parasitoids. Methods: We measured fruit (syconia) set per tree, seed set per syconium, and fig-wasp numbers (pollinators and non-pollinators) per syconium in a total of 62 trees in 24 populations covering three distributional zones - the dry, western margin of the species’ range, a more mesic, eastern margin at the species’ altitudinal limit, and the zone between these two margins. These results were modelled against F. rubiginosa population size, the position of plant populations in relation to range margins, and climatic gradients of temperature and rainfall. Results: Lower rates of pollinator parasitism and less pollinator competition correlated with increased reproductive success in the pollinator and increased male fitness (in terms of pollen dispersal) and female fitness (in terms of seed per syconium) in isolated trees of F. rubiginosa, compared with trees in larger populations, particularly at F. rubiginosa’s mesic, expanding range margin. Main conclusions: Pollinator-predator release and pollinator-competition release can lead to increased pollinator and plant reproductive success in pioneer trees at range margins. This reinforces the need to understand biotic interactions underlying reproduction and dispersal at expanding range fronts if we are to understand and better predict the drivers and effects of climate-change-induced range shifts in plants and their pollinators.
- PublicationInteractions between two species of recently-sympatric invasive honeybees: Apis cerana induces aggression in Apis mellifera during foraging(University of New England, 2019)
; ; ; ; Paini, DeanHoneybees Apis mellifera (European honeybee) and Apis cerana (Asian honeybee) are cosmopolitan, having colonized continents beyond their natural ranges. In tropical Australia, these alien species have recently become sympatric. The environmental and economic impacts of these species when in sympatry remain to be seen; however, any interspecific competition may be of significance. We examined conspecific and heterospecific interactions between honeybees foraging at the nectar- and pollen-providing flowers of Antipogon leptopus (Polygonaceae). We cross-classified 554 encounters by three variables; incoming bee species, resident bee species, and one of four potential responses: (1) incoming defers to resident; (2) incoming procures the flower from resident; (3) incoming and resident share the flower; or (4) both incoming and resident abandon the flower. We also measured aggression and foraging rates of workers at flowers. Both species visited similar numbers of flowers in a foraging bout and spent similar foraging times on individual flowers. Incoming A. mellifera were more likely to procure flowers from resident A. cerana, and incoming A. cerana were more likely to defer to resident A. mellifera. A. mellifera were more aggressive toward heterospecifics than conspecifics, with heterospecifics 4.5 times more likely to provoke an aggressive response. However, no significant difference between conspecific and heterospecific aggression was observed for incoming A. cerana. A. mellifera were less abundant, yet overall more likely to acquire flowers and use aggression to do so. Costs of aggression may help explain the population-scale dominance of A. cerana over A. mellifera in this study. - PublicationCan the native Rusty Fig, Ficus rubiginosa, beat climate change?(2018-04-14)
; ; ; This study investigated aspects of male and female reproductive success in a widespread, keystone dry-rainforest species, Ficus rubiginosa, the Rusty Fig. The primary aim of the study was to determine if climate change was impacting on reproductive success in F. rubiginosa and/or was likely to impact in the future. Four key questions relevant to plant population ecology in fragmented landscapes are addressed: Question 1. What impacts do climatic variation and fig-population fragmentation have on flowering and fruiting phenology in F. rubiginosa trees growing in a temperate, seasonal environment? Question 2. What impacts do climatic variation and fig-population fragmentation have on pollinator dispersal among F. rubiginosa trees and, if there are impacts, what are the consequences for pollen dispersal and fruit set? Question 3. What impacts do climatic variation and fig-population fragmentation have on frugivore visitation to F. rubiginosa and, if there are impacts, what are the consequences for seed dispersal? Question 4. What have the long-term patterns of dispersal and range extension by F. rubiginosa been in eastern Australia? Field work concentrated in the western half of F. rubiginosa's range in northern New South Wales, Australia. Four key areas of population ecology relating to phenology, pollination success, avian visitation and genetic variation were addressed. Environmental factors impacting on FF. rubiginosa's fitness in these four areas were identified and measured over a three-year period between January 2014 and January 2017. Further field work was conducted over the 3,000 km range of the species in July to October 2015 to collect genetic samples for Next Generation Sequencing and Single Nucleotide Polymorphism analysis to determine current and historic patterns of genetic variation across the species' fragmented distribution.
Major findings from this study were that phenology was impacted by temperature and rainfall. Low winter temperatures caused syconium development to slow down and go into stasis. Low rainfall stimulated the extension of male and female phenophases in trees through staggered syconium development, which increased reproductive assurance but reduced the number of ripe fruit on trees, thereby reducing a tree's attractiveness to frugivore seed-dispersers. Pollination success was reduced in drier parts of F. rubiginosa's range compared with that in more mesic environments. Extreme fragmentation - single trees - provided pollinators with refuge from parasitoids leading to increased male and female fitness in F. rubiginosa. Retention of unpollinated fruit on trees increased female fitness by increasing apparent crop size and attracting greater visitation by frugivores. Ficus rubiginosa was a pivotal and keystone resource for twice as many insectivorous bird species as frugivore species. Drier climates during the last ice age led to contraction of F. rubiginosa populations to four probable refugia, scattered over 22° (2,500 km) of latitude. Dry coastal zones that functioned as biogeographic barriers to gene flow during the last ice age have functioned as corridors facilitating dispersal more recently.
Signals of early population decline can be difficult to recognise in long-lived species such as large Ficus trees. However, several factors that impacted on pollination success and seed production in F. rubiginosa were identified during this project. Among these factors was fire, projected to keep increasing in frequency and intensity under the influence of climate change. Flower and fruit production was delayed by up to five years and more in many trees across the study area, as trees recovered (resprouted) after fire. Lower rainfall resulted in slower and reduced fruit production, and fruit that were produced were smaller and had fewer seeds. Smaller crops of ripe fruit in trees attracted lower avian visitation and, hence, reduced seed dispersal. Lower pollination success was recorded during drier conditions. And gene flow was obstructed by dry areas between populations. All of these factors and events point to reductions in fitness and early population decline. They are all consequences of deteriorating rainfall and increasing temperatures, which have been experienced across the study area over the last few decades. Further decline is likely and local population extinctions are possible in those parts of F. rubiginosa's range where climate change results in further reductions in rainfall and ongoing increases in temperature. This will negatively impact on the communities F. rubiginosa lives in and on ecosystem services the affected plants and animals provide within the local and surrounding environments.
Ficus rubiginosa would be an important species to use in restoration as it provides a year-round food resource for frugivores and, as found in this study, a year-round and unique food resource for insectivorous woodland birds, many of which are in decline in this region and others globally.
- PublicationBetween Art and Poetry: New Perspectives on Tablelands FloraBetween Art and Poetry is a collaboration between botanical writer John Charles Ryan and botanical artist David Mackay on the diversity and beauty of the natural environments and, in particular, the flora of the New England Tablelands. Held at Reader's Companion in Armidale in November 2017, the main event included a reading of poetry, an art exhibition, brief talks by John and David, a musical performance by Alana Blackburn and the launch of two books, The Language of Plants and Plants in Contemporary Poetry. The goal of Between Art and Poetry is to foster greater dialogue between the arts and sciences. The project aims to improve communication and enhance mutual understanding between the visual and literary arts, on the one hand, and between the arts and environmental science, on the other. The general purpose of the collaboration is to raise public awareness of the diversity and fragile beauty of the natural environments that surround us in the New England region. The art-science collaboration centred on six plant species of the New England Tablelands: Antarctic beech (Nothofagus moorei), southern giant stinging tree (Dendrocnide excelsa), Ingram's wattle (Acacia ingramii) , rock orchid (Dendrobium speciosum), river sheoak (Casuarina cunninghamiana) and Port Jackson fig (Ficus rubiginosa). While some species, such as Ingram's wattle, are highly localised endemics, others - for instance, river sheoak - are distributed more broadly across the Tablelands, coastal eastern Australia and, indeed, other parts of the globe.
- PublicationTwo decades of demography reveals that seed and seedling transitions limit population persistence in a translocated shrubBackground and Aims: 'Olearia flocktoniae' is an endangered shrub that was passively translocated from its natural ecosystem, where it has since gone extinct. This study aimed to determine sensitivities vital to populations persisting in human-created areas. Methods: Population colonization, longevity and extinction were investigated over 20 years using 133 populations. Seed-bank longevity was determined from germination trials of seeds exhumed from extinct and extant sites via a 10-year glasshouse trial and by 'in situ' sowing experiments. From 27 populations, 98 cohorts were followed and matrix models of transitions from seeds to adults were used to evaluate the intrinsic rate of population growth against disturbance histories. Ten populations (38 cohorts) with different disturbance histories were used to elevate sensitivities in vital rates. Key Results: Most populations had few individuals (~30) and were transient (<5 years above ground). The intrinsic population growth rate was rarely >1 and all but two populations were extinct at year 20. Seeds were short-lived 'in situ'. Although >1000 seeds per plantwere produced annually in most populations, sensitivity analysis showed that the transition to the seed bank and the transition fromthe seed bank to seedlings are key vulnerabilities in the life-cycle. Conclusions: Seedling establishment is promoted by recent disturbance. Increasing the number of disturbance events in populations, even severe disturbances that almost extirpate populations, significantly increases longerterm population persistence. Only populations that were disturbed annually survived the full 20 years of the study. The results show that translocated populations of 'O. flocktoniae' will fail to persist without active management.
- PublicationUnsuccessful introduced biocontrol agents can act as pollinators of invasive weeds: Bitou Bush ('Chrysanthemoides monilifera ssp. rotundata') as an example(John Wiley & Sons Ltd, 2017)
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