Concerns about widespread human-induced declines in insect populations are mounting, yet little is known about how land-use change modifies the dynamics of insect communities, particularly in understudied biomes. Here we examine how the seasonal patterns of ant activity, key drivers of ecosystem functioning, vary with human-induced land cover change on a subtropical island landscape. Using trap captures sampled biweekly from a biodiversity monitoring network covering Okinawa Island, Japan, we processed 1.2 million individuals and reconstructed activity patterns within and across habitat types. We determined that communities inside the forest exhibited more variability than those in more developed areas. Using time-series decomposition to deconstruct this pattern, we found that ant communities at sites with greater human development exhibited diminished seasonality, reduced synchrony, and higher stochasticity compared to those at sites with greater forest cover. We demonstrate that our results cannot be explained by variation in either regional or in situ temperature patterns, or by differences in species richness or composition among sites. We conclude that the breakdown of natural seasonal patterns of functionally key insect communities may comprise an important and underappreciated consequence of global environmental change that must be better understood across Earth's biomes.
Two major human-caused threats to ecosystems are habitat modification and the increasing frequency and intensity of extreme weather events. To study the combined effect of these threats, the authors used acoustic monitoring of bats along a habitat modification gradient on the island of Okinawa, Japan. During the observation period, the island experienced numerous typhoons and one supertyphoon. Native bat species remained active even at high wind speeds (up to 30 m/s in some cases). Milder typhoons had no observable effect on bat populations, with activity levels fully recovering within a few hours or days. The super typhoon also did not seem to affect bats in fully or partially forested habitats but caused their local disappearance at the urban site, which they have not re-colonized three years after the event. Notably, bats that disappeared at the urban site were species roosting in well-protected places such as caves and concrete structures. In all cases, the biomass of small flying insects and the acoustic activity of insects recovered within days after extreme weather events. Thus, the striking difference between habitats in supertyphoon effects on bats cannot be explained by the super typhoon directly killing bats, destroying their roosting sites, or decreasing the abundance of their prey. The results underscore the importance of preserving natural habitats in areas particularly affected by changing climate and show that the survival of species and ecosystems during the numerous episodes of climate change in the Earth’s history does not necessarily mean their ability to survive the accelerating climate change of our time.
Pipistrelles of the genus Hypsugo are among the rarest bats in Japan, known from a handful of records. In June 2018, a sequence of echolocation calls apparently by a bat of this genus was recorded by an automatic ultrasound recorder on the island of Okinawa. The calls closely resemble H. pulveratus, a Chinese species never before recorded in Japan, and H. alaschanicus, a very rare species in Japan. They also resemble calls of Hypsugo sp. bats from a small population recently discovered on nearby Amami-Oshima island. The extreme rarity in our recordings, combined with lack of detection in Okinawa by other surveys, suggests that the individual was a vagrant. However, given the cryptic nature of the species on Amami, it remains possible that there is a small and likely endangered resident population, underlining the need for further bat surveys on Okinawa and other Nansei Islands.
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