Mountain-climbing bears protect cherry species from global warming through vertical seed dispersal

Abstract

In a warming climate, temperature-sensitive plants must move toward colder areas, that is, higher latitude or altitude, by seed dispersal [1]. Considering that the temperature drop with increasing altitude (-0.65°C per 100 m altitude) is one hundred to a thousand times larger than that of the equivalent latitudinal distance [2], vertical seed dispersal is probably a key process for plant escape from warming temperatures. In fact, plant geographical distributions are tracking global warming altitudinally rather than latitudinally, and the extent of tracking is considered to be large in plants with better-dispersed traits (e.g., lighter seeds in wind-dispersed plants) [1]. However, no study has evaluated vertical seed dispersal itself due to technical difficulty or high cost. Here, we show using a stable oxygen isotope that black bears disperse seeds of wild cherry over several hundred meters vertically, and that the dispersal direction is heavily biased towards the mountain tops. Mountain climbing by bears following spring-to-summer plant phenology is likely the cause of this biased seed dispersal. These results suggest that spring- and summer-fruiting plants dispersed by animals may have high potential to escape global warming. Our results also indicate that the direction of vertical seed dispersal can be unexpectedly biased, and highlight the importance of considering seed dispersal direction to understand plant responses to past and future climate change.

The primacy of bears as seed dispersers in salmon‐bearing ecosystems

“…We did not find clear evidence of species partitioning resources across an elevation gradient, with brown bears feeding across a large elevation as observed by Naoe et al. (), although black bears consumed fruit at a higher elevation on average and rarely at low elevation (Fig. ).…”

Lags in the response of mountain plant communities to climate change

“…Indeed, animal‐dispersed plants are perhaps better able to track climate change than those relying on wind or passive dispersal. For example, bears disperse seeds of cherry trees upwards several hundred metres in elevation as they follow plant phenology during the summer season (Naoe et al., ), and birds regularly disperse seeds across large distances (Viana, Santamaría, & Figuerola, ). Interactions with animal vectors could therefore accentuate variation among plants in spread rates.…”

Negative correlation between altitudes and oxygen isotope ratios of seeds: exploring its applicability to assess vertical seed dispersal

“…Some of the samples of P. verecunda in 2012–2014 had also been used previously (Naoe et al. ). We analyzed three seeds per fruiting tree.…”

“…In particular, it plays a key role in plant escape and/or expansion under climate change (Corlett and Westcott ; Naoe et al. ). This role becomes more important during intensive climate change including present global warming (ref.…”

“…Naoe et al. () found a negative correlation between altitudes and δ 18 O of wild cherry seeds and then determined the altitude of the mother plant of a dispersed seed using δ 18 O of the dispersed seed. As a result, they determined vertical seed dispersal distance, that is, the vertical distance between a dispersed seed and its mother plant (see Fig.…”