Geographical patterns of butterfly species diversity in the subtropical Ryukyu Islands: the importance of a unidirectional filter between two source islands

Abstract

Aim To examine the roles of geohistorical and ecological factors in the development of butterfly assemblages on continental islands with multiple source pools.Location The Ryukyu Islands, Japan. This arc of continental islands is located between two source islands, Kyushu and Taiwan, and contains two major straits, the Tokara and Kerama gaps.Methods A total of 489 butterfly species were identified on 59 islands, including the two source islands. The influences on species richness and rarity of latitude, area, elevation, and distances from the nearest source and from the nearest larger island were analysed using generalized linear models. The relationships between differences in area, elevation, and distance and dissimilarity between island butterfly faunas were evaluated by multiple regressions on distance matrices. The relationships between area, elevation, and distance from the source and dissimilarity to the source fauna were examined using linear models. The dissimilarity was based on the Sørensen index and its nestedness and turnover components.Results Latitude, area and isolation determined species richness and rarity, whereas differences in elevation and distance regulated species turnover between islands. The gaps between islands were associated with nestedness between island faunas. Area consistently had a negative relationship with the total dissimilarity to source fauna. The overall dissimilarity to Kyushu decreased with the distance from Kyushu, whereas dissimilarity to Taiwan increased with distance from Taiwan.Main conclusions Both environmental filtering and dispersal limitation determine the geographical patterns of butterfly assemblages in the Ryukyus. The present study focuses on the unique pattern wherein migration from Kyushu is facilitated on islands farther from Kyushu, while migration from Taiwan is inhibited on islands farther from Taiwan. The two source islands have contrasting roles that affect butterfly distributions unidirectionally. This study highlights the importance of resolving dissimilarity into nestedness and turnover components to elucidate the formation of island biota.

Dispersal modality determines the relative partitioning of beta diversity in spider assemblages on subtropical land‐bridge islands

“…We found that 94% of the global datasets on island systems that we screened had a high (> 0.5) contribution of species replacement to multiple‐island dissimilarity, indicating that species turnover generally dominates beta diversity across various biological groups. For example, extreme contributions of species replacement to multiple‐island dissimilarity were found in island butterflies in Lake Kenyir, Malaysia (Yong et al ., ) and the Ryukyu Island, Japan (Hirao et al ., ). One explanation for these patterns of predominant turnover could be sampling effects, which can be a potential explanation for at least some variance in turnover between islands in most biogeographical studies, particularly as the Simpson index is sensitive to a large number of zero values (Dapporto et al ., , ).…”

“…Studies in insular biogeography that assess the contributions of the various groups of factors in determining compositional dissimilarities may be confounded by joint effects of geological age, historical events, multiple source pools, climate and human disturbance (Fattorini, ; Dennis et al ., ; Hirao et al ., ). The natural laboratories created by hydroelectric damming, such as the Thousand Island Lake in eastern China, can tease these factors apart (Benchimol & Peres, ; Wilson et al ., ).…”

“…However, most previous studies have been conducted at broad continental scales, and the mechanisms behind variation in species composition might be masked or confounded by, for example, strong local or regional effects (Ricklefs, ). To date, few studies on the partitioning of beta diversity have been conducted in island systems (but see Dapporto et al ., ; Heiser et al ., ; Hirao et al ., ; Si et al ., ; Vodă et al ., ).…”

Reconciling Darwin’s naturalization and pre‐adaptation hypotheses: An inference from phylogenetic fields of exotic plants in Japan

“…A broad range of latitudinal (22°N to 45°N) and altitudinal (0–3,776 m) gradients across these archipelagos create diverse climatic conditions, including subtropical, temperate and hemiboreal zones. During the Pliocene and the Pleistocene, geological processes intermittently divided the islands or periodically connected islands through land‐bridge corridors (Hirao, Kubota, & Murakami, ). These climatic and geographical conditions have resulted in a region‐specific endemic flora (Kubota, Kusumoto, Shiono, & Tanaka, ; Kubota et al, ).…”

Community variation of spiders, beetles and isopods in three small island groups of the Aegean Sea: the interplay between history and ecology

“…Several biogeographical drivers, such as area and distance from mainland and/or other islands, have been shown to exert a direct effect on species richness as well as on compositional dissimilarity patterns in archipelagos (Guerrero et al ., ; Hausdorf & Hennig, ; Fattorini, ,b, ,b; Pitta et al ., , ; Cabral et al ., ; Carvalho & Cardoso, ). Also palaeogeographic history, reflected in current inter‐island distances/connections, and distances from the mainland or possible connection intervals during past geological time periods is expected to be most influential on compositional dissimilarity patterns in continental archipelagos (Hausdorf & Hennig, ; Fattorini, ,b, ; Hirao et al ., ). Recently, it has been shown that palaeogeographic history, i.e.…”