Body-size dependent foraging strategies in the Christmas Island flying-fox: implications for seed and pollen dispersal within a threatened island ecosystem

Abstract

Background Animals are important vectors for the dispersal of a wide variety of plant species, and thus play a key role in maintaining the health and biodiversity of natural ecosystems. On oceanic islands, flying-foxes are often the only seed dispersers or pollinators. However, many flying-fox populations are currently in decline, particularly those of insular species, and this has consequences for the ecological services they provide. Knowledge of the drivers and the scale of flying-fox movements is important in determining the ecological roles that flying-foxes play on islands. This information is also useful for understanding the potential long-term consequences for forest dynamics resulting from population declines or extinction, and so can aid in the development of evidence-based ecological management strategies. To these ends, we examined the foraging movements, floral resource use, and social interactions of the Critically Endangered Christmas Island flying-fox (Pteropus natalis). Methods Utilization distributions, using movement-based kernel estimates (MBKE) were generated to determine nightly foraging movements of GPS-tracked P. natalis (n = 24). Generalized linear models (GLMs), linear mixed-effect models (LMMs), and Generalized linear mixed-effects model (GLMMs) were constructed to explain how intrinsic factors (body mass, skeletal size, and sex) affected the extent of foraging movements. In addition, we identified pollen collected from facial and body swabs of P. natalis (n = 216) to determine foraging resource use. Direct observations (n = 272) of foraging P. natalis enabled us to assess the various behaviors used to defend foraging resources. Results Larger P. natalis individuals spent more time foraging and less time traveling between foraging patches, traveled shorter nightly distances, and had smaller overall foraging ranges than smaller conspecifics. Additionally, larger individuals visited a lower diversity of floral resources. Conclusions Our findings suggest that smaller P. natalis individuals are the primary vectors of long-distance dispersal of pollen and digested seeds in this species, providing a vital mechanism for maintaining the flow of plant genetic diversity across Christmas Island. Overall, our study highlights the need for more holistic research approaches that incorporate population demographics when assessing a species’ ecological services.

Individual behaviour shapes patterns of bird‐mediated seed dispersal

“…The two seed dispersal strategies were not associated with differences in bird body mass or relative wing length, which is contrary to what has been found in previous studies of animal seed dispersers (Larsen & Burns, 2012; Todd et al., 2022; Wotton & Kelly, 2012). Thus, our results suggest that nutcrackers are not primarily limited by morphology for their seed dispersal behaviour and that the decision to pursue either behavioural strategy must be more strongly influenced by other factors.…”

“…The use of spatially explicit movement data has been highlighted to improve our understanding of seed dispersal patterns, as successful seed dispersal depends first, on the exact movement of an individual and second, on the characteristics of the habitat patch where seeds are deposited (Auffret et al., 2017; Schupp et al., 2010). However, studies that use spatially explicit movement data to investigate seed dispersal patterns remain sparse (but see Kays et al., 2011; Oleksy et al., 2015; Piazzon et al., 2012; Rodríguez‐Pérez et al., 2012; Santamaría et al., 2007; Todd et al., 2022).…”

Close-kin mark-recapture informs critically endangered terrestrial mammal status

“…Christmas Island is a territory of Australia located 1500 km west of the Australian mainland. Samples and measurements from individual CIFF were collected across the island during multiple sampling exercises for several different studies 19 , 24 , 39 , 40 (see “ Methods ” for a detailed description). Wing-membrane biopsies for each individual were taken and stored in ethanol for genetic analyses.…”

“…The decline of the CIFF, which is paralleled by that of other fauna on the island (including the extinction of the island’s only other bat species, Pipistrellus murrayi in 2009), has serious implications for the health of Christmas Island’s ecosystem. The CIFF is a keystone species that plays an important role in seed dispersal and pollination processes on the island 15 , 23 , 24 . Definitive demographic estimates for the CIFF population are essential to the management of this species but are difficult to obtain because of the CIFF’s cryptic nature, high mobility, the difficulty in accessing parts of the island, and incomplete knowledge of the species’ habitat use 16 , 23 , 24 .…”

“…The CIFF is a keystone species that plays an important role in seed dispersal and pollination processes on the island 15 , 23 , 24 . Definitive demographic estimates for the CIFF population are essential to the management of this species but are difficult to obtain because of the CIFF’s cryptic nature, high mobility, the difficulty in accessing parts of the island, and incomplete knowledge of the species’ habitat use 16 , 23 , 24 .…”