图1 传粉昆虫下降背景下授粉生态弹性不同机制示意图。以土地类型变化为代表的全球变化引起传粉昆虫群落结构变化。在①功能冗余、②密度补偿、③响应多样性、④连接周转; ⑤跨尺度弹性机制作用下, 传粉功能团保障传粉功能(如植物柱头上沉降花粉数量)在可接受的水平, 形成授粉生态弹性。

Fig. 1 The framework showing the different mechanisms of ecological resilience of pollination in the face of pollinator decline. The global changes, such as land use change, invoke the variations in pollinator community. Under the mechanisms of ①functional redundancy, ②density compensation, ③response diversity, ④interaction turnover; ⑤cross-scale resilience, pollinator communities are able to deliver an acceptable level of pollination functioning (e.g. pollen grains on stigma surface), forming the ecological resilience of pollination.

图2 不同传粉功能团间功能冗余引起授粉生态弹性的机制示意图。假设生态系统中3个传粉功能团(a、b和c)均为开花植物授粉(A), 当传粉功能团a沉降的花粉(黄色)数量和传粉功能团c沉降的花粉(橙色)数量下降时, 传粉功能团b沉降的花粉(蓝色)数量增加(B)。柱头花粉数总量保持不变, 传粉昆虫群落形成授粉生态弹性。

Fig. 2 Conceptual diagram showing the mechanical effect of functional redundancy among functional groups of pollinators on ecological resilience of pollination. Three functional groups (a, b and c) are supposed to pollinate the flowering plants in the ecosystems (A). When the amount of pollens delivered by functional group a (yellow) and functional group c (orange) decreases, the amount of pollens delivered by functional group b (blue) increases (B). The number of pollens deposited on stigma surfaces does not change. The pollinator communities have the ecological resilience of pollination.

图3 密度补偿作用引起授粉生态弹性的机制示意图。假设生态系统存在传粉功能团a和传粉功能团b (A), 全球变化下生态系统由功能团a的4个体和功能团b的5个体的传粉昆虫群落(A)转变为功能团a的2个体和功能团b的9个体的传粉昆虫群落(B)。当生态系统内传粉功能团a访花频率下降时, 传粉功能团b访花频率上升, 反之亦然(B)。虽然不同传粉功能团传粉效率(如单次访花花粉沉降量)存在差异, 但沉降花粉数量保持不变, 形成授粉生态弹性。

Fig. 3 Conceptual diagram illustrating the mechanical effect of density compensation on ecological resilience of pollination. Two functional groups of pollinators (a and b) are supposed to deliver pollens on stigma surfaces (A). In the face of global changes, the pollinator communities with 4 individuals of functional group a and 5 individuals of functional group b (A) is transformed to a different pollinator communities with 2 individuals of functional group a and 9 individuals of functional group b (B). The visit density of functional group a decreases, but the visit density of functional group b increase, and vice versa (B). Due to the differences in pollination efficiency (e.g. pollen deposition per visit), the overall pollen numbers delivered by different pollinator communities are the same. The pollinator communities have the ecological resilience of pollination.

图4 响应多样性引起授粉生态弹性的机制示意图。假设传粉功能团在个体大小和巢穴位置等响应性状方面表现出多样性, 不同个体大小的传粉昆虫(A)对自然生境的空间响应尺度存在差异, 个体大的传粉昆虫响应尺度大于个体小的传粉昆虫(B)。同时, 不同巢穴位置的传粉昆虫(C)种群数量对自然生境呈现不同的响应规律, 部分传粉昆虫种群数量随自然生境百分率的下降而下降, 但其他传粉昆虫种群数量保持不变甚至增长(D)。传粉功能团的响应多样性可能通过效应多样性调节传粉功能, 使植物柱头花粉沉降数量保持不变, 形成授粉生态弹性(E)。

Fig. 4 Conceptual diagram showing the mechanical effect of response diversity on ecological resilience of pollination. Pollinators are supposed to be different in body size and nesting site. The pollinators with different body sizes (A) respond to natural habitats at different spatial scales, with a relatively large scale of effect for the large pollinators compared to a relatively small scale of effect for the smaller pollinators (B). Meanwhile, the pollinators with different nesting sites (C) respond differently to the natural habitats, with a decrease of populations for most pollinators along the loss of semi-natural habitats but an increase or stability of populations for other pollinators (D). Response diversity can affect ecosystem pollination functioning through effect diversity. The overall pollen numbers delivered by pollinators keep the same. The pollinator communities have the ecological resilience of pollination (E).

图5 连接周转引起授粉生态弹性的机制示意图。在生态系统中, 假设原传粉网络存在3种传粉昆虫(a1, a2, a3)和3种开花植物(p1, p2, p3) (A)。干扰作用下, 传粉昆虫和开花植物间部分连接消失但新的连接形成, 网络连接发生重连(B); 或者传粉昆虫下降, 对应的连接消失, 或新的传粉昆虫(a4)进入网络, 建立新连接, 传粉昆虫发生物种周转(C)。在传粉网络重连和物种周转的共同作用下, 传粉昆虫和开花植物形成传粉网络连接周转(D)。对开花植物来说, 连接周转前后传粉昆虫群落组成存在差异, 但原传粉网络中的传粉昆虫和连接周转后的传粉昆虫传播等量花粉, 形成授粉生态弹性(E)。黑线示意周转前传粉昆虫同开花植物间的联系, 红线示意形成的新连接。

Fig. 5 Conceptual diagram illustrating the mechanical effect of interaction turnover on ecological resilience of pollination. The ecosystem is hypothesized to have an original pollination network with three pollinators (a1, a2, a3) and three plants (p1, p2, p3) (A). Under disturbances, some interactions are lost but new interactions occur, forming interaction rewiring (B). Interactions are also lost as a result of pollinators decline, but new interactions is built as new pollinators (a4) enter the pollination network, resulting from species turnover of pollinators (C). The combined effect of interaction rewiring and species turnover explains an interaction turnover of the pollination network (D). For plants, their pollinator assemblages are different before and after interaction turnover, however, the amount of pollens delivered by the pollinator assemblages is the same. The pollinator communities have the ecological resilience of pollination (E). Black lines indicate the original interactions before interaction turnover and red lines indicate newly-built interactions after interaction turnover.

图6 跨尺度弹性引起授粉生态弹性的机制示意图。在生态系统中, 假设空间分布的开花植物a、b、c、d、e和f存在大、中、小3种传粉功能团, 传粉功能团空间传粉尺度(或空间搜索范围)分别约为300 m、1,000 m和1,500 m, 个体大的传粉昆虫空间跨尺度为开花植物传粉(A)。3种传粉功能团在个体大小(body size)轴上形成不连续性的分布(B)。开花植物a接收3个传粉功能团传粉, b、d和f接收2个传粉功能团传粉, c和e仅接收1个传粉功能团传粉, 因此开花植物a的传粉功能团跨尺度传粉功能冗余程度高于其他开花植物(C)。以开花植物a为对象, 当某搜索范围(如300 m)的传粉功能团访花密度下降时, 其他尺度(如1,500 m)的传粉功能团增加访花密度, 传播等量花粉, 形成授粉生态弹性(D)。在(C)和(D)中, 线条长度示意对应的传粉昆虫空间传粉范围, 线条宽度示意传粉昆虫空间传粉功能。

Fig. 6 Conceptual diagram showing the mechanical effect of cross-scale resilience on ecological resilience of pollination. The ecosystems are hypothesized to have three functional groups with large (1,500 m), medium (1,000 m) and small (300 m) spatial scales (i.e., foraging ranges), respectively, and they pollinate flowering plants a, b, c, d, e and f spatially distributed in ecosystems. The large-sized functional groups pollinate plants across scale (A). The three functional groups of pollinators are distributed discontinuously along the x-axis of body size (B). Flowering plant a is pollinated by three functional groups, flowering plant b, d and f are pollinated by two functional groups, and flowering plant c and e are pollinated by just one functional groups. Therefore, the level of cross-scale redundancy of pollinator assemblages for plant a is higher than that of other plants (C). If the visit density of a certain functional group of pollinators with a specific foraging range (e.g. 300 m) declines (e.g. plant a), other functional groups of pollinators with a large spatial foraging range (e.g. 1,500 m) increase their visit densities. The amount of pollens delivered by the pollinator assemblages on the stigma surface of plant a is similar. The pollinator communities have the ecological resilience of pollination (D). In (C) and (D), the lengths of lines corresponding to the pollinators indicate the foraging ranges of pollinators and the widths of lines quantify their pollination functioning.