Spatial networks differ when food supply changes: Foraging strategy of Egyptian fruit bats

Abstract

Animals are faced with a range of ecological constraints that shape their behavioural decisions. Habitat features that affect resource abundance will also have an impact, especially as regards spatial distribution, which will in turn affect associations between the animals. Here we utilised a network approach, using spatial and genetic data, to describe patterns in use of space (foraging sites) by free-ranging Egyptian fruit bats (Rousettus aegyptiacus) at the Dakhla Oasis in Egypt. We observed a decrease in home range size during spring, when food availability was lowest, which was reflected by differences in space sharing networks. Our data showed that when food was abundant, space sharing networks were less connected and more related individuals shared more foraging sites. In comparison, when food was scarce the bats had few possibilities to decide where and with whom to forage. Overall, both networks had high mean degree, suggesting communal knowledge of predictable food distribution.

Egyptian fruit bats do not preferentially roost with their relatives

“…Selection of roosts with high betweenness may facilitate access to information in a similar manner as proposed for the tree‐roosting giant noctules ( Nyctalus lasiopterus , Fortuna et al ., 2009). Moreover, as spring is the season of scarce food resources, we propose that multiple core roosts during this season may be beneficial for information transfer regarding suitable foraging sites (Bachorec et al ., 2020).…”

“…Consequently, we propose that these ‘socially exploratory’ fruit bats are likely to play an important role in connecting and providing valuable information to individuals that do not roost together (Whitehead, 2008; Chaverri, 2010; Farine & Whitehead, 2015). Though we have no evidence for information transfer, we presume that association with and/or following of these central individuals may facilitate access to public information on roosting or foraging sites (Bachorec et al ., 2020).…”

“…Since grouping with kin reduces numerous costs and having more relatives as roost mates could result in easier access to information on both roosting and foraging sites (Wilkinson, 1992; Rossiter et al ., 2002; Frank, 2003), we hypothesized a link between relatedness and roost sharing. As our previous results have shown that food resources become scarce in spring (Bachorec et al ., 2020), we investigated two distinct seasons, comparing data from winter and spring. As food distribution is likely to affect foraging associations, there could be associated impacts on roosting associations and dynamics related to a need for increased information transfer.…”

Social networks based on frequency of roost cohabitation do not reflect association rates of Myotis lucifugus within their roosts

“…to change between years due to births, deaths, dispersal, and addition of tagged bats. We chose to construct these networks based upon the entire maternity season because our goal was to use intraroost networks to evaluate cohabitation networks, which are typically based on seasons (Bachorec et al, 2020;Chaverri, 2010) or years (Kerth et al, 2011;Wilkinson et al, 2019). Data collected from Mammoth readers in 2017 were not included because antennas were placed in areas within the roost that few bats visited, and antennas were relocated in 2018.…”

Timing of emergence and cave return, and duration of nocturnal activity in an endemic Malagasy fruit bat

“…These studies found that time of emergence and return to day roost sites also varied according to season, age, sex, and depended on the intraspecific variation in a range of ecological parameters. The availability of food is an important component in this relation and Lučan et al (2016) and Bachorec et al (2020) have shown a negative correlation between fruit bat home range and food availability. Similar relations have been noted in other groups of mammals, for example, the rodent Octodon degus (Molina, 1782) (Octodontidae), which spent more time outside their burrows foraging during the nonreproductive period because of food scarcity compared to breeding period (Ebensperger and Hurtado 2005).…”