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Current decline of the ‘‘Dodo Tree’’: a case of broken-down interactions with extinct species or the result of new interactions with alien invaders

  • January 2006
  • In book: Emerging Threats to Tropical Forests (pp.Chicago University Press)
  • Edition: 1st
  • Publisher: Chicago University Press
  • Editors: William F. Laurance, Carlos A. Peres
Authors:
Claudia Baider at Agricultural Services, Ministry of Agro-Industry and Food Security
Claudia Baider
  • Agricultural Services, Ministry of Agro-Industry and Food Security
Francois Benjamin Vincent Florens at University of Mauritius
Francois Benjamin Vincent Florens
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In W. F. Laurance and C.A. Peres. (eds). 2006.
Emerging Threats to TropicalForests. The University
of Chicago University Press, Chicago.
... Although all frugivores have the potential to contribute to seed dispersal to varying degrees, those that generally predate on seeds are functionally different because they are likely to contribute much less to the recruitment success of native plants. For example, the percentage of seeds destroyed after handling can be up to 100% for macaques Macaca fascicularis on Mauritius because they pick unripe fruits before seeds become viable [41][42][43] , and studies from other locations have reported percentages of 86% for pigs (Sus scrofa 44 ) and~65% for rats (Rattus rattus 45 ). The replacement of extinct interactions with novel ones has resulted in a 36% (304-196) reduction in seed dispersal interactions and an increase of 54% of mostly seeddestructive interactions. ...
... There have been substantial losses of plant-frugivore interactions on Mauritius as a consequence of animal extinctions, leading to the formation of a novel seed-disperser network with native plants, potentially leading to different ecological dynamics. The gain of a similar number of novel plant-frugivore interactions probably did not compensate for potential losses in seed dispersal, because the key introduced frugivores are often seed predators that generally destroy a large proportion of handled seeds (e.g., up to 100% for macaques [41][42][43] , 86% for pigs 44 and~65% for black rats 45 , Supplementary Data 3). In addition, the maximum size of seeds that can be swallowed by seed dispersers has decreased, while that of seed predators has increased, which could negatively affect large-seeded plant recruitment. ...
... At present, the severely reduced, fragmented, and disturbed natural habitats in Mauritius make it difficult for some plants and frugivores to interact by reducing range overlap 34 and causing local extinctions 47 . Other influencing factors are reduced encounter rates between species due to their rarity 13,54 , reduced fruit set because of nutrient competition with invasive plants 55,56 , destruction of fruits and flowers by monkeys and rats before they ripen [41][42][43]47 , and possibly reduced pollination due to pesticide use. The many intensive conservation efforts in Mauritius have been successful in increasing the population sizes of critically endangered plants and animals, weeding out invasive plants and reducing invasive animal densities 57 . ...
Novel plant–frugivore network on Mauritius is unlikely to compensate for the extinction of seed dispersers
Article
Full-text available
  • Feb 2023
Insular communities are particularly vulnerable to anthropogenic extinctions and introductions. Changes in composition of island frugivore communities may affect seed dispersal within the native plant community, risking ecological shifts and ultimately co-extinction cascades. Introduced species could potentially mitigate these risks by replacing ecological functions of extinct species, but conclusive evidence is lacking. Here, we investigate changes in plant–frugivore interactions involving frugivorous birds, mammals and reptiles in Mauritius, an oceanic island with an exceptionally well-specified frugivore community and well-described species introduction history. We demonstrate substantial losses of binary interaction partnerships (at the species level) resulting from native species extinctions, but also gains of equal numbers of novel interactions with introduced species, potentially supporting the idea that non-native species might compensate for lost seed dispersal. However, closer investigation of animal seed handling behaviour reveals that most interactions with seed dispersers are replaced by ecologically different interactions with seed predators. Therefore, restoration of seed dispersal functionality in this novel plant–frugivore community is unlikely.
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... Thus, delaying germination beyond a critical threshold of dryness would lead to lower recruitment for recalcitrant species whose regeneration depends more on seedling stocks in the forest understory than on seeds persisting in soil banks (Hopkins & Graham 2006). Finally, although most studies have focused on the role of seed coat scarification (Barnea et al. 1991;Soltani et al. 2018;Traveset 1998) or even fantasized obligatory plant/seed-coat scarificator interactions (see the criticism of Temple [1977] in Baider & Florens [2006] for the iconic case of the dodo and the tambalacoque tree for instance), non-innate dormancy due to flesh persistence alone may be a major handicap for a large number of fleshy-fruited tree species (Rogers et al. 2021 PREPRINT). ...
... The focal species are large-seeded (mean seed diameter of 12 mm in L. calophylloides and 24 mm in M. balata) and typical species of the Sapotaceae family that grow as long-lived shade-tolerant trees in mature tropical rainforests (Levi & Peres 2013;Mahandran et al. 2018). These trees are often dominant in native lowland canopies and not threatened like other large-seeded Sapotaceae in the Mascarenes (Baider & Florens 2006;Cadet 1977;Strasberg 1996), despite their incapacity to recolonize the vast areas of historical lava flows due to frugivore loss (Albert et al. 2020b). Both species have been massively planted by the French National Office in the area of Saint-Philippe. ...
... Seed and fruit predation by R. rattus has already been reported for Sapotaceae seeds in the Mascarenes (Baider & Florens, 2006;Eric Rivière, pers. comm.), that is why we took into account the potential impact of this introduced species. ...
Tree recruitment after native frugivore extinction? A field experiment to test the impact of fruit flesh persistence in a tropical oceanic island
Article
  • Jun 2022
The loss of large frugivores leads to seed dispersal loss and regeneration failure of numerous large-seeded trees near mother trees. Although Janzen–Connell effects are considered as the primary underlying cause, other factors remain understudied. Here, we used a field experiment to test the impact of flesh persistence on the recruitment of two large-seeded Sapotaceae species that lost their dispersers. In the rainforest of Mare Longue (Réunion), we sowed 3840 seeds in a four-factor design: seed treatment (seed cleaning; flesh persistence), canopy closure (understory; gap), year of sowing (01/2018; 11/2019) and species ( Labourdonnaisia calophylloides , Mimusops balata ). We also used camera traps to evaluate the impact of extant vertebrates. Seed treatment was by far the most influential factor: flesh persistence led to seedling recruitment divided by 3,2 on average, mainly due to failure of germination or seedling emergence. There were also significant variations in recruitment between species, years and canopy closure levels, notably due to the behaviour of the invasive fauna, especially giant snails that could unexpectedly restore recruitment by feeding on fruit flesh. Together, our results demonstrate strongly depleted recruitment due to flesh persistence and the importance of field experiments to understand the processes at work in complex ecosystems with novel plant–animal interactions.
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... A decline among smaller diameter woody native plants (>2.5 to <10 cm DBH) is also apparent when comparing with studies done in the 1980s [87,88]. A closer tree by tree monitoring through time between adjacent weeded and nonweeded native forests showed native tree mortality to be increased by the presence of invasive alien plants at both community [89] and population levels [90]. Even native trees that largely overtop the alien plants are dying faster when growing within stands of alien plants [90], indicating that root interactions alone suffice in increasing mortality of native trees. ...
... A closer tree by tree monitoring through time between adjacent weeded and nonweeded native forests showed native tree mortality to be increased by the presence of invasive alien plants at both community [89] and population levels [90]. Even native trees that largely overtop the alien plants are dying faster when growing within stands of alien plants [90], indicating that root interactions alone suffice in increasing mortality of native trees. This elevated native tree mortality is generating an inexorable loss of suitable host plants for epiphytic orchids. ...
... The invasion by alien plants has also been shown to be reducing the extent of flowering of native woody plants [90,94] as well as the production of fruits [90,94,95] hence of seeds too, resulting in a much lowered native plant regeneration in forests invaded by alien plants [93]. Invasive plants also reduce growth rate of native trees [90], which in turn is expected to result in smaller trees with fewer opportunities for epiphytic orchids to grow on, as well as feeding back into reduced seed production and regeneration because smaller trees typically carry fewer fruits. ...
Diversity, Ecology, and Conservation of Mauritius Orchids
Chapter
  • Jan 2022
Mauritius was one of the last places on Earth to be colonized by humans offering one of the most complete history of what native species occurred originally and what was lost, when, and why. This situation can therefore serve as a laboratory to study human impacts in the current age of human-driven species extinction. Mauritius is also one of the most human-impacted places, thereby reflecting what awaits much of the tropics as human impacts intensify. We used available literature, herbarium samples, and personal observations and studies on the Orchidaceae to characterize its diversity, distribution and ecology, and the human-induced threats they face, to better inform their conservation in Mauritius. There are 91 native orchid species from 30 genera recorded on the island. Twenty species (22%) appear extinct, although some may survive undetected. New species and records continue to be added. Only 10% of the species are endemic to Mauritius, and 80% are unique to the south-west Indian Ocean islands. Most species are epiphytic, and the highest diversity occurs in native forests of the wet uplands. Mauritian orchids, particularly the larger ones, face many threats, some inexorably worsening. There exists much room to improve knowledge about Mauritian orchids that would better inform their conservation which is today still very neglected. This includes taxonomic research, detection of ecological patterns and trends, ecology of the species, as well as quantification and hierarchization of threats to prioritize conservation management. Studying Mauritius native orchids helps understand how devastating, sustained, and accelerating the many threats that human activities pose to orchid biodiversity can be and which await other countries currently less human-impacted than Mauritius.
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... A decline among smaller diameter woody native plants (>2.5 to <10 cm DBH) is also apparent when comparing with studies done in the 1980s [87,88]. A closer tree by tree monitoring through time between adjacent weeded and nonweeded native forests showed native tree mortality to be increased by the presence of invasive alien plants at both community [89] and population levels [90]. Even native trees that largely overtop the alien plants are dying faster when growing within stands of alien plants [90], indicating that root interactions alone suffice in increasing mortality of native trees. ...
... A closer tree by tree monitoring through time between adjacent weeded and nonweeded native forests showed native tree mortality to be increased by the presence of invasive alien plants at both community [89] and population levels [90]. Even native trees that largely overtop the alien plants are dying faster when growing within stands of alien plants [90], indicating that root interactions alone suffice in increasing mortality of native trees. This elevated native tree mortality is generating an inexorable loss of suitable host plants for epiphytic orchids. ...
... The invasion by alien plants has also been shown to be reducing the extent of flowering of native woody plants [90,94] as well as the production of fruits [90,94,95] hence of seeds too, resulting in a much lowered native plant regeneration in forests invaded by alien plants [93]. Invasive plants also reduce growth rate of native trees [90], which in turn is expected to result in smaller trees with fewer opportunities for epiphytic orchids to grow on, as well as feeding back into reduced seed production and regeneration because smaller trees typically carry fewer fruits. ...
Diversity, Ecology, and Conservation of Mauritius Orchids
Chapter
  • Aug 2021
Mauritius was one of the last places on Earth to be colonized by humans offering one of the most complete history of what native species occurred originally and what was lost, when, and why. This situation can therefore serve as a laboratory to study human impacts in the current age of human driven species extinction. Mauritius is also one of the most human-impacted places, thereby reflecting what awaits much of the tropics as human impacts intensify. We used available literature, herbarium samples, and personal observations and studies on the Orchidaceae to characterize its diversity, distribution and ecology, and the human-induced threats they face, to better inform their conservation in Mauritius. There are 91 native orchid species from 30 genera recorded on the island. Twenty species (22%) appear extinct, although some may survive undetected. New species and records continue to be added. Only 10% of the species are endemic to Mauritius, and 80% are unique to the south-west Indian Ocean islands. Most species are epiphytic, and the highest diversity occurs in native forests of the wet uplands. Mauritian orchids, particularly the larger ones, face many threats, some inexorably worsening. There exists much room to improve knowledge about Mauritian orchids that would better inform their conservation which is today still very neglected. This includes taxonomic research, detection of ecological patterns and trends, ecology of the species, as well as quantification and hierarchization of threats to prioritize conservation management. Studying Mauritius native orchids helps understand how devastating, sustained, and accelerating the many threats that human activities pose to orchid biodiversity can be and which await other countries currently less human-impacted than Mauritius.
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... One such strategy could be the control of invasive alien species, particularly those that may reduce natural food resources for flying foxes directly (e.g. long-tailed macaques on Mauritius (Baider & Florens, 2006)) or indirectly (for example through foraging habitat degradation). Invasive alien species are major drivers of habitat degradation, particularly on islands (Caujapé-Castells et al., 2010). ...
... Additionally, invasive alien plants can compete with native plants reducing their fitness (Brown & Mitchell, 2001;McKinney & Goodell, 2010;Stinson et al., 2006;Vilà et al., 2011) and may contribute to a major decrease in large tree density (Florens, Baider, Marday et al., 2017). Conversely, habitat restoration by controlling alien plants can increase growth rate, flowering and fruiting of native trees (Baider & Florens, 2006;Monty, Florens & Baider, 2013), leading to increased native tree regeneration and species richness (Baider & Florens, 2011). Notably, this includes species whose fruits are eaten by Pteropus (Florens, Baider, Marday et al., 2017). ...
... G. Krivek, et al. Journal for Nature Conservation 54 (2020) 125805 previously noted in several other species bearing fleshy fruits (Auchoybur & Florens, 2005;Baider & Florens, 2006;Monty, Florens, & Baider, 2013), suggesting that this trend is general. However, other processes may affect this outcome. ...
Invasive alien plant control improves foraging habitat quality of a threatened island flying fox
Article
Full-text available
Flying foxes play keystone ecological roles in plant reproduction. Yet, they face numerous threats, including persecution for eating commercial fruits. This human-wildlife conflict has recently escalated to culling campaigns of a threatened flying fox on Mauritius. Finding non-lethal solutions to this human-wildlife conflict on the island is therefore extremely important. We hypothesized that invasive alien plants may reduce native fruit availability through competition and that weeding alien plants could improve the native foraging habitat quality of flying foxes – in turn, reducing their consumption of commercially important fruits. We compared native fruit production and foraging intensity of the Mauritian flying fox (Pteropus niger) in forests weeded of alien plants a decade previously and adjacent non-weeded forests. Fruits and ejecta were collected weekly during five months under 144 randomly chosen native trees of two canopy species whose fruits are eaten by flying foxes. Intraspecific variations in tree and fruit traits were used to examine flying fox foraging preference. Native fruit production was significantly higher in weeded forests for both tree species, and this was matched by higher flying fox foraging intensity. Flying foxes preferred large trees and fed predominantly on large and ripe fruits. The predominant consumption of ripe fruits emphasizes the importance of flying foxes as seed dispersers. Our results indicate that alien plant invasion substantially reduces native fruit production and that weeded forests provide a much better habitat for flying foxes. Our findings lend support to invasive alien plant control as a management strategy in mitigating such human-wildlife conflicts.
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... Commercial fruit trees in particular offer more easily accessible and concentrated food resources compared to forests where fruits are more scattered due to the large diversity of tree species which often do not fruit simultaneously (Plotkin et al. 2000;Wills et al. 2006). This situation is particularly acute in Mauritius where invasive alien plants cause a reduction of native fruit production in forests (Baider and Florens 2006;Monty, Florens, and Baider 2013;Krivek et al. 2020). Generally, P. niger tends to roost closer to foraging sites (Figure 2), with animals tending to leave forest areas to roost closer to orchards during the fruiting season of commercial trees, particularly in the north-west and west of the island. ...
... Additionally, restoration, through weeding of invasive alien plants, is important to pre-empt further habitat degradation. Indeed, weeding is known to increase the flowering and fruiting of native trees (Baider and Florens 2006;Monty, Florens, and Baider 2013), which would consequently improve the foraging habitat quality of P. niger (Krivek et al. 2020) and likely reduce their reliance on commercial fruits. However, most of the habitat restoration on the mainland occurs at higher elevations (>250 m). ...
Foraging and roosting patterns of a repeatedly mass-culled island flying fox reveals opportunities to mitigate human–wildlife conflict
Article
  • Aug 2022
Human–wildlife conflicts (HWC) arising from fruit bats eating commercial fruits is a worsening problem worldwide and is epitomized by the Mauritian flying fox (Pteropus niger), a species threatened with extinction yet repeatedly mass-culled since 2015. Non-lethal solutions for dealing with this HWC are needed, which are rooted in the evidence available. In this study, we tracked the movements of 12 flying fox individuals over two years in order to document the animal’s movement ecology, with a view to deriving recommendations to alleviate the ensuing HWC. We found that flying foxes prefer to forage and roost in forested areas located at elevations < 250 m. However, during the fruiting season of commercial trees, the animals tended to roost closer to and forage more often on commercial fruits during the early hours of the night. These findings have several implications for the improvement of commercial fruit protection, which should in turn alleviate HWC, notably through informing management to take into consideration the spatio-temporal expression of flying fox foraging.
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... In this case, i.e. "hand-cleaning of seeds", germination can be seen, but in the case of "flesh persistence" modality, only the emergence of seedlings from the fruit can be properly assessed. Photos: A. Gorissen Seed and fruit predation by Rattus rattus have already been reported for Sapotaceae seeds in the Mascarenes (Baider and Florens, 2006;Eric Rivière, pers. comm.), that is why we took into account the potential impact of this introduced seed predator. ...
... Thus, the reward that has been selected to effectively disperse large seeds in a highly competitive environment via frugivory (Eriksson et al., 2000), may become alone a major handicap for large-seeded plants when mutualist partners disappear from the ecosystem. However, our results are not in line with those of Baider and Florens (2006) that claim seed cleaning to have no effect on the germination rate of Sideroxylon grandiflorum (Sapotaceae) on Mauritius. Even if their weak sampling (only 32 fruits) may considerably limit the scope of their results, the negative impact of flesh persistence might be all the more important as the ratio of pulp to seed is high. ...
Rupture des interactions mutualistes plantes à fruits charnus-vertébrés frugivores, et conséquences sur la régénération des forêts tropicales dans les Mascareignes
Thesis
Full-text available
  • Dec 2020
Les forêts tropicales sont largement dominées par les plantes à fruits charnus dont la dispersion est assurée par les vertébrés frugivores. L'effondrement global des grands vertébrés interroge donc quant à la résilience de ces écosystèmes, en particulier dans les îles qui concentrent l’essentiel des extinctions documentées. Les Mascareignes sont un remarquable système d'étude des ruptures d'interactions de frugivorie car la faune d'origine, pléthorique jusqu'à la colonisation humaine au 17ème siècle et aujourd'hui largement éteinte, est bien connue tout comme sa flore diversifiée qui compte parmi les plus menacées. La Réunion abrite encore des forêts indigènes le long de puissants gradients environnementaux et un volcanisme actif offrant l'opportunité d'explorer sur le long terme les conséquences de la défaunation. De plus, les niveaux variables d'extinction de vertébrés forestiers entre La Réunion (principal frugivore relictuel, masse=55 g) et Maurice (450 g) permet d'utiliser ces îles comme pseudo-réplicats pour tester diverses hypothèses. Cette thèse s'organise en trois parties qui visent à (1) décrire les patrons de distribution spatiale des traits de dispersion à La Réunion et Maurice, et comprendre les implications pour l'extinction de la faune qui a été fulgurante à La Réunion ; (2) évaluer les conséquences de la rupture des interactions de frugivorie sur la reconstruction des écosystèmes forestiers sur les coulées de lave du Piton de la Fournaise ; (3) évaluer les conséquences de la rupture des interactions de frugivorie sur le maintien de la diversité dans les forêts de l'archipel établies avant la colonisation humaine. (1) Les proportions de plantes à fruits charnus dans les communautés de plantes ligneuses chutent avec l'altitude et cette diminution est d'autant plus forte que les fruits sont gros. En comparant les principaux facteurs d'extinction de vertébrés entre La Réunion et Maurice, nous montrons que la destruction précoce des habitats favorables de basse altitude à La Réunion a probablement joué un rôle central dans la fulgurance des extinctions. (2) Après avoir étoffé la chronoséquence des coulées du Piton de la Fournaise, nous montrons que la disparition des populations de frugivores a profondément altéré la capacité des forêts de basse altitude à se rebâtir dès le 18ème siècle et que la refaunation des écosystèmes avec des frugivores introduits profite essentiellement aux plantes exotiques à fruits charnus. Néanmoins, en restaurant la dispersion, les plantes à grosses graines sont capables de s'installer sur les coulées historiques où recrutent très majoritairement des plantes envahissantes. (3) En comparant les forêts de référence de La Réunion et Maurice, nous montrons que la roussette noire permet un bien meilleur recrutement de nombreuses espèces ligneuses à Brise-Fer que le bulbul de La Réunion à Mare-Longue, excepté pour les plantes à grosses graines qui se régénèrent assez mal dans les deux îles. Une expérimentation à Mare-Longue montre enfin comment la persistance de la pulpe seule peut limiter fortement le recrutement, mais que ce dernier peut être notablement influencé par la faune introduite. Nos résultats inquiétants montrent l'urgence de protéger les grands frugivores indigènes où ils existent encore et de favoriser leur retour quand ils ont disparu. Parallèlement, des semis à large échelle devraient être envisagés dans les aires protégées où le maintien, voire le retour de la dynamique forestière indigène sont impératifs.
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... However, hundreds of hectares of native forests were cleared of invasive alien plants since early 1990s, much of which coincides with the bird's distribution. Such a conservation measure should have elicited population recovery for a bird like H. olivaceus given its diet of fruits, nectar and insects (Safford, 1996) as alien plant control leads to greater abundances of those resources (Baider & Florens, 2006;Florens, Mauremootoo, Fowler, Winder, & Baider, 2010;Monty, Florens, & Baider, 2013). Therefore, some other compensatory or limiting factor appears to be preventing recovery of the bird population. ...
... For example, invasive alien plants like the strawberry guava (Psidium cattleyanum Sabine), an invader on many other tropical islands worldwide (Tuler, Proença, Carrijo, & Peixoto, 2018), reaches high densities in most wet native vegetation of Mauritius , including all current localities of R. simplex (apart from Pétrin where it has been weeded). These alien plants are known to reduce native plant flowering and fruiting (Baider & Florens, 2006;Monty et al., 2013), tree density and regeneration (Baider & Florens, 2011) and are thus likely to be negatively impacting R. simplex. ...
Non-intrusive systematic study reveals mutualistic interactions between threatened island endemic species and points to more impactful conservation
Article
Oceanic islands harbour a disproportionately large share of extinct and endangered birds worldwide and up to about 6,800 highly threatened plants, stressing the urgency for conservation efforts there. However, effective conservation action can only be as sound as the ecological understanding on which it is based. Knowledge about the ecology of threatened birds and plants can be relatively sketchy even in well-studied oceanic islands and this can potentially misdirect or erode conservation actions’ effectiveness. We used camera traps to document vertebrate flower visitors of a threatened, mono-specific endemic oceanic island plant (Roussea simplex) that produces much nectar and which was abundant until the 1930s before declining severely despite its presence mostly within protected areas. We determined proportions of native and alien flower visitors in four populations and characterised their ecological role (e.g. florivore, nectar robber, pollinator) through observations and exclusion experiments alongside experiments to determine seed sets by agamospermy, autogamy, geitonogamy and xenogamy. Five native and three alien vertebrate species visited flowers (N = 5,085 camera trap-hours), 96.6% of visits being from birds. Among endemics, 74-96% of visits were by the Mauritius Bulbul (Hypsipetes olivaceus), a threatened bird able to effect pollination contrary to the other endemic birds. Roussea simplex is primarily xenogamous, producing 2657 ± 480 seeds, and seed set dropped markedly when the bird was excluded (861.8 ± 91.0 SE, Kruskal-Wallis χ2 = 14.2, p < 0.001). Natural seed set was very low (410.0 ± 85.3 SE) where the bird was locally extinct or very rare. Invasive alien rats (Rattus rattus) and long-tailed macaques (Macaca fascicularis) were important florivores or nectar robbers. Systematic non-intrusive study using camera traps combined with manipulative experiments revealed a mutualism between two relatively well-studied threatened endemic species as well as new threats from alien vertebrates acting as nectar robbers and florivores. Roussea simplex’s major decline within protected areas and its abundant and year round flowering and nectar production point to a major hitherto unrecorded drop in floral resource previously available to at least five endemic species, and particularly to its commonest flower visitor and principal pollinator, the threatened Mauritius Bulbul. These findings exemplify how systematic non-intrusive study of threatened species may radically change conservation managers’ priorities which in the current case should focus primarily on controlling alien rats and macaques and re-instating or reinforcing Bulbul-Roussea mutualism as each would be more impactful than addressing gecko-Roussea mutualism disruption by alien ants which so far was the only recorded threat thought to drive the rapid decline of Roussea simplex. Our study underscores that current conservation efforts should also pay particular attention to medium to longer-term changes in habitat or community composition which may not be obvious from merely considering extent and composition of current habitats.
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Foraging Strategies of Invasive Macaca fascicularis may Promote Plant Invasion in Mauritius
Article
Full-text available
The effectiveness of seed dispersal by frugivorous primates may vary between seasons and plant species, depending on foraging strategies. We investigated how foraging strategies of an invasive frugivorous primate (the long-tailed macaque, Macaca fascicularis) affect seed dispersal effectiveness (SDE) between native and invasive plants in Mauritius’ native remnant forests. By collecting behavioural data on a group of partially habituated macaques via scan sampling from December 2019 until December 2020 (mean 19.2 ± SD 7.3 hours per month), we investigated seasonal patterns in diet, home range, and fruit availability to identify foraging strategies and determine fruit preference. We simultaneously assessed SDE for invasive vs native plants by quantifying native and invasive fruits consumed or dropped intact by macaques during feeding bouts (n = 114). Macaques fed increasingly on ripe invasive fruits and less on other food items as fruit availability increased, due to preference for invasive fruits and disproportionate availability of invasive vs native fruits. When fruit became scarcer, macaques had larger home ranges, increasingly fed on scarce unripe native and invasive fruits, and expanded their diet by eating orchard crops, indicating use of energy-maximizing strategies. Macaques consumed more native than invasive fruits when unripe and commonly destroyed seeds of native fruits, indicating higher SDE for invasive vs native plants. Higher discard rates of unripe compared to ripe fruits further reinforced these differences in SDE. Our results highlight potential facilitation of plant invasion by an invasive primate, due to foraging strategies shaped by the availability of invasive fruits.
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First come, first served: fruit availability to keystone bat species is potentially reduced by invasive macaques
Article
  • Feb 2021
Bats provide important pollination and seed-dispersal services to native angiosperms. However, many bat species are increasingly threatened by human disturbance, including the Mauritian flying fox (Pteropus niger), an endemic, keystone seed disperser. Native forests are scarce and P. niger frequently feeds in commercial plantations, where it now is considered a pest and subjected to frequent culling, thereby hindering conservation efforts. The invasive long-tailed macaque (Primates: Cercopithecidae, Macaca fascicularis) potentially competes with P. niger for scarce native fruits. We investigated the extent of dietary overlap between M. fascicularis and P. niger on Mauritius by sampling fruit drop for 17 tree species and identifying additional food species along line transects. Fruits of 13 of 17 species were eaten by animals and fruit production across tree replicates generally was low but highly variable. Although M. fascicularis ate only 4% of fruit overall, they consumed 20–100% of the fruits of seven species. Approximately 39% of dropped fruits were intact; based on field observations, most probably were dropped by M. fascicularis. Unlike P. niger, M. fascicularis ate mostly unripe fruit and depleted all fruit of certain species at an unripe stage. Hence, M. fascicularis may restrict P. niger’s diet and potentially disrupt seed dispersal of some tree species. Furthermore, small trees are more prone to fruit depletion at an unripe stage by macaques. In addition, asynchronous fruiting phenology across forest fragments may modulate the provision of native fruits to P. niger throughout the year. Although competition can be demonstrated only by controlled experimental studies that are logistically impossible in our scenario, our results highlight potential detrimental consequences that introduced frugivores may have on keystone seed dispersers. Finally, our results suggest that a more integrative and island-wide approach to forest restoration may be valuable for the conservation of P. niger.
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