高寒草甸植物物种丧失对草原毛虫的影响

doi:10.17520/biods.2022069

摘要/Abstract

摘要：

植物多样性是调控食物网结构和生态系统功能最重要的生物因素, 植物多样性丧失深刻影响食草动物, 但由于小型食草动物种群数量波动明显、统计随机性较大等困难, 我们对植物多样性丧失如何影响小型食草动物依然知之甚少。基于在青藏高原高寒草甸设置的长期植物物种剔除试验, 本研究于2016-2020年7-8月连续调查了植物物种剔除各处理中草原毛虫(Gynaephora alpherakiif)的数量, 分析了植物物种及功能群丧失对草原毛虫的影响。结果表明, 虽然时空差异及统计随机性是影响草原毛虫数量变化的主要因素, 但植物物种剔除介导的群落差异对草原毛虫数量的影响依然显著: (1)在各观测时段, 优势种线叶嵩草(Kobresia capillifolia)的丧失导致群落中草原毛虫数量显著减少; 禾草类物种丧失也会减少草原毛虫数量, 但其影响仅在8月显著; (2)杂类草物种丧失通过增加群落中禾草物种多度, 可增加草原毛虫数量; 豆科物种丧失使莎草增多, 也会增加草原毛虫数量; (3)各植物功能群部分物种剔除并未显著影响草原毛虫数量。本研究证实了高寒草甸中草原毛虫数量会因优势植物嵩草和禾草的多度减少或禾草物种丧失而显著减少, 但群落总生物量、个体数和物种丰富度、豆科多度以及各功能群植物同比减少, 都对草原毛虫数量没有明显影响。这些结果说明在随机作用主导下, 植物群落中的特定功能群相对多度(而非物种多样性)变化深刻影响草原毛虫适合度, 进而影响生态系功能及服务; 未来生物多样性研究及草地虫害生物防控中应更多考虑统计随机性及植物功能多样性对小型食草动物的影响。

关键词: 物种多样性, 群落构建, 统计随机性, 重复测量, 功能群, 功能性状

Abstract

Aims: Plant diversity plays a crucial role in regulating food web dynamics and ecosystem functioning. Existing studies have documented significant impact on large herbivores and ecosystem functioning from loss in plant species diversity. Yet, little is known about effect of plant diversity loss on small herbivores and its functional consequence on food web dynamics, ecosystem functioning and ecosystem service, due to difficulty in distinguishing the role of plant diversity from larger fluctuations of small herbivore populations under the confounding effect of multiple ecological factors and demographic stochasticity.

Methods: Based on our long-term experiment of plant species removal in an alpine meadow on the Tibetan Plateau, we repeatedly measured the number of grassland caterpillar (Gynaephora alpherakiif) in each plot (i.e. density) in July and August over five years (2016-2020). We examined the effect of plant species removal on caterpillar population by associating changes in caterpillar counts with a shift in plant community attributes following plant removal and using a set of generalized linear mixed models.

Results: Plant removal induced a difference in the plant community, which significantly and consistently influenced the caterpillar counts over years and months independent of the observed variation in caterpillar counts accounted for by the difference in years and observational times within each month. Comparing the caterpillar counts in plots without removing plant species, (i) the caterpillar counts decreased in plots subjected to removal of dominant species (Kobresia capillifolia) in both July and August across five years, and increased in plots subjected to removal of forbs species in August of 2016 and 2019, and (ii) the caterpillar counts tended to increase in plots subjected to removal of legume species but only significantly in few cases, and did not significantly differ with plots subjected to removal of partial species (accounting for 20% aboveground biomass) of each functional groups. Further analysis showed that neither total aboveground biomass nor plant species richness and total individual numbers was significantly correlated with the caterpillar counts. The variation in caterpillar counts was associated positively with aboveground biomass of sedges and grasses as well as grass species richness, but negatively with the amount of forbs and legumes. The structural equation model further revealed that the removal of Kobresiaand grass species affected caterpillar counts through decreasing aboveground biomass of graminoids, but increasing graminoids following removal of forb and legume species promoted the density of caterpillars.

Conclusion: Based on field observations on the grassland caterpillar populations in plots subjected to different removal protocols, our study provides robust evidence that the decline in relative abundance of graminoids significantly reduced the fitness of caterpillars, and thus potentially impacts grassland functioning and ecosystem service. This study also suggests that future research on biodiversity effects and biological control of pests needs to pay more attention to the effects of plant functional diversity and demographic stochasticity on small herbivores.

Key words: species diversity, community assembly, demographic stochasticity, repeated measurement, functional group, functional traits

雍青措姆, 习新强, 牛克昌 (2022) 高寒草甸植物物种丧失对草原毛虫的影响. 生物多样性, 30, 22069. DOI: 10.17520/biods.2022069.

Yongqingcuomu , Xinqiang Xi, Kechang Niu (2022) Effect of plant species loss on grassland caterpillar in alpine meadows. Biodiversity Science, 30, 22069. DOI: 10.17520/biods.2022069.

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链接本文: https://www.biodiversity-science.net/CN/10.17520/biods.2022069

https://www.biodiversity-science.net/CN/Y2022/V30/I11/22069

图/表 5

表1 利用广义线性模型评估年、月、重复测量和植物物种剔除处理对草原毛虫数量的影响效应。模型估计的斜率(均值 ± 标准差)表示影响的方向(正数为增加、负数为减小)、程度(斜率数值大小)及其显著性(* P < 0.05, ** P < 0.001)。

Table 1 Effect of year, month, repeated measurement and plant species removal on counts of grassland caterpillar assessed by generalized linear mixed models (GLMM). The tabular (estimated) slopes (mean ± SD) from GLMM measured the effect of fixed factors on caterpillar counts, with direction, strength and significance of the effects indicated by + (increased) or - (decreased), absolute size of value and * (* P < 0.05, ** P < 0.01), respectively. Ksp: Removal of Kobresia capillifoli; Gsp: Removal of grass species; Fsp: Removal of forb species; Lsp: Removal of legume species; Psp: Removal of partial species for each functional group.

影响效应 Effect size
年际影响 Effect of years (变异解释 Variability = 10.7%, F = 114.6^**, df = 4)
2017 vs. 2016	0.28 ± 0.03^**
2018 vs. 2016	0.12 ± 0.03^**
2019 vs. 2016	-0.54 ± 0.04^**
2020 vs. 2016	-0.44 ± 0.04^**
月份影响 Effect of months (变异解释 Variability = 1.9%, F = 16.3^**, df = 5)
8月vs. 7月August vs. July	-0.04 ± 0.02
重复测量影响 Effect of repeated measurement (变异解释 Variability = 40.8%, F = 48.8^**, df = 36)
第一次 1st vs. 0th observation	-0.36 ± 0.03^**
第二次 2nd vs. 0th observation	-0.70 ± 0.03^**
第三次 3rd vs. 0th observation	-0.84 ± 0.03^**
第四次 4th vs. 0th observation	-1.2 ± 0.04^**
植物剔除处理影响 Effect of plant removal (变异解释 Variability = 8.3%, F =1.5^**, df = 230)
剔除优势嵩草vs.对照 K_sp vs. CK	-0.29 ± 0.04^**
剔除禾草物种vs.对照 G_sp vs. CK	-0.19 ± 0.04^**
剔除杂类草物种vs.对照 F_sp vs. CK	0.12 ± 0.03^**
剔除豆科物种vs.对照 L_sp vs. CK	0.06 ± 0.03
各功能群部分物种剔除vs.对照 P_sp vs. CK	-0.02 ± 0.03
残差 Residuals (变异解释 Variability = 38.4%, df = 1,653)

影响效应 Effect size
年际影响 Effect of years (变异解释 Variability = 10.7%, F = 114.6^**, df = 4)
2017 vs. 2016	0.28 ± 0.03^**
2018 vs. 2016	0.12 ± 0.03^**
2019 vs. 2016	-0.54 ± 0.04^**
2020 vs. 2016	-0.44 ± 0.04^**
月份影响 Effect of months (变异解释 Variability = 1.9%, F = 16.3^**, df = 5)
8月vs. 7月August vs. July	-0.04 ± 0.02
重复测量影响 Effect of repeated measurement (变异解释 Variability = 40.8%, F = 48.8^**, df = 36)
第一次 1st vs. 0th observation	-0.36 ± 0.03^**
第二次 2nd vs. 0th observation	-0.70 ± 0.03^**
第三次 3rd vs. 0th observation	-0.84 ± 0.03^**
第四次 4th vs. 0th observation	-1.2 ± 0.04^**
植物剔除处理影响 Effect of plant removal (变异解释 Variability = 8.3%, F =1.5^**, df = 230)
剔除优势嵩草vs.对照 K_sp vs. CK	-0.29 ± 0.04^**
剔除禾草物种vs.对照 G_sp vs. CK	-0.19 ± 0.04^**
剔除杂类草物种vs.对照 F_sp vs. CK	0.12 ± 0.03^**
剔除豆科物种vs.对照 L_sp vs. CK	0.06 ± 0.03
各功能群部分物种剔除vs.对照 P_sp vs. CK	-0.02 ± 0.03
残差 Residuals (变异解释 Variability = 38.4%, df = 1,653)

图1 利用广义线性混合模型评估各年份和月份高寒草甸植物物种剔除处理对草原毛虫数量的影响效应。与对照组群落中(CK)毛虫数量(a)相比, 植物物种剔除处理对群落中毛虫数量的影响方向及大小(b-f)以广义线性混合模型中固定因子的斜率(及95%置信区间)表示, 植物剔除处理显著(* P < 0.05, ** P < 0.001)增加(正值)或减小(负值)的影响以带*的蓝色正或红色负斜率值(置信区间与零不相交)表示, 无*的灰色斜率值(置信区间与零相交)为影响不显著。

Fig. 1 Effect of plant species removal on numbers of grassland caterpillar in each year and month in a Tibetan alpine meadow assessed by generalized linear mixed models (GLMM). Comparing to caterpillar counts in plots (CK) without removing plant species (a), the effect of plant species removal in each year and month on the caterpillar counts indicated by values and 95% confidence interval (CI) of estimated slopes from GLMM, with significant (95% CI not overlap with zero, * P < 0.05, ** P < 0.01) positive (blue) and negative (red) effect highlighted by colored values with * and CI of the estimated slopes, and values without * and CI (overlap with zero) indicated non-significant difference between CK and treatment of plant species removal. Ksp, Gsp, Fsp, Psp, CK and Lsp see Table 1.

表2 利用广义线性模型评估多年植物物种剔除处理对植物群落属性的影响。表中数据为广义线性模型的固定因子(年际和植物种剔除处理)对因变量(植物基本属性)的变异解释(%)、差异显著性(F值)、斜率(均值 ± 标准差), 表示固定因子对因变量影响的方向(正数为增加、负数为减小)和程度(斜率数值大小)及其显著性(粗体为P < 0.1, * P < 0.05, ** P < 0.001)。

Table 2 Effect of year and plant species removal on plant community attributes assessed by linear mixed models (GLMM). The tabular values from GLMM measured the effect of fixed factors (year and treatment of plant species removal) on plant community attributes, including accounted variability (%), significance test of difference (F-value with P-value), and estimated slopes (mean ± SD) that indicate direction (+ increased, - decreased) and strength (absolute size of value) of effect of difference in year (each year vs. 2016) or in plant species removal (each treatment vs. CK plots without removing any species) on plant community attributes, with significance highlighted by bold (P < 0.1) and * (* P < 0.05, ** P < 0.01). Ksp, Gsp, Fsp, Psp, CK and Lsp see Table 1.

	物种丰富度 Species richness	总个体数 Total individuals	总生物量 Total biomass	各功能群生物量 Biomass for each functional group
	物种丰富度 Species richness	总个体数 Total individuals	总生物量 Total biomass	莎草 Sedges	禾草 Grasses	杂类草 Forbs	豆科 Legumes
年际影响 Effect of years
变异解释 Variability (%)	34.5%	49.7%	79.9%	50.9%	20.2%	46.8%	26.8%
F	139.8^**	127.7^**	455.6^**	193.1^**	75.7^**	226.9^**	57.9^**
自由度 df	3	3	3	3	3	3	3
影响效应 Effect size (与2016年比, 各年的影响以斜率均值 ± 标准差衡量 Effect size of year vs. 2016 was measured by mean ± SD of slopes)
2017	0.06 ± 0.02	0.26 ± 0.01^**	-81.5 ± 2.7^**	-25.7 ± 1.5^**	-2.9 ± 1.5	-45.6 ± 2.5^**	-7.1 ± 0.6^**
2019	0.29 ± 0.03^**	0.66 ± 0.01^**	-51.5 ± 2.7^**	-11.8 ± 1.4^**	-1.7 ± 1.5	-35.9 ± 2.5^**	-4.6 ± 0.6^**
2020	0.30 ± 0.03^**	0.51 ± 0.01^**	-89.8 ± 2.7^**	-25.8 ± 1.4^**	-17 ± 1.5^**	-44.9 ± 2.5^**	-4.4 ± 0.6^**
物种剔除影响 Effect of species removal
变异解释 Variability (%)	39.8%	9.7%	1.90%	22.3%	52.6%	32.1%	28.3%
F	24.1^**	3.7^**	1.62^*	12.7^**	29.6	23.4^**	9.2^**
自由度 df	20	20	20	20	20	20	20
影响效应 Effect size (与对照比, 各处理的影响以斜率均值 ± 标准差度量 Effect size of treatment vs. CK was measured by mean ± SD of slopes)
剔除优势嵩草 K_sp	-0.05 ± 0.03	-0.11 ± 0.01^**	-5.4 ± 3.3	-11.4 ± 1.8^**	-1.7 ± 1.8	-4.8 ± 3.1	-0.5 ± 0.7
剔除禾草物种 G_sp	-0.20 ± 0.03^**	-0.11 ± 0.01^**	-7.70 ± 3.3^*	-0.36 ± 1.8	-14.4 ± 1.9^**	7.8 ± 3.1^*	-0.5 ± 0.7
剔除杂类草物种 F_sp	-0.45 ± 0.04^**	-0.30 ± 0.01^**	-8.0 ± 3.3^*	6.0 ± 1.8^**	19.2 ± 1.9^**	-31.1 ± 3.1^**	5.7 ± 0.7^**
剔除豆科物种 L_sp	-0.07 ± 0.03^*	-0.09 ± 0.01^**	-7.6 ± 3.3^*	-0.42 ± 1.8	-0.5 ± 1.8	-4.7 ± 3.1	-2.3 ± 0.8^**
各功能群部分物种剔除 P_sp	-0.11 ± 0.03^**	-0.19 ± 0.01^**	-3.7 ± 3.3	-3.8 ± 1.7^*	-2.7 ± 1.8	-1.7 ± 3.1	1.1 ± 0.7
残差 Residuals
变异解释 Variability (%)	25.7%	40.5%	18.2%	26.9%	27.2%	21.2%	45.0%
自由度 df	312	312	312	306	306	308	292

	物种丰富度 Species richness	总个体数 Total individuals	总生物量 Total biomass	各功能群生物量 Biomass for each functional group
	物种丰富度 Species richness	总个体数 Total individuals	总生物量 Total biomass	莎草 Sedges	禾草 Grasses	杂类草 Forbs	豆科 Legumes
年际影响 Effect of years
变异解释 Variability (%)	34.5%	49.7%	79.9%	50.9%	20.2%	46.8%	26.8%
F	139.8^**	127.7^**	455.6^**	193.1^**	75.7^**	226.9^**	57.9^**
自由度 df	3	3	3	3	3	3	3
影响效应 Effect size (与2016年比, 各年的影响以斜率均值 ± 标准差衡量 Effect size of year vs. 2016 was measured by mean ± SD of slopes)
2017	0.06 ± 0.02	0.26 ± 0.01^**	-81.5 ± 2.7^**	-25.7 ± 1.5^**	-2.9 ± 1.5	-45.6 ± 2.5^**	-7.1 ± 0.6^**
2019	0.29 ± 0.03^**	0.66 ± 0.01^**	-51.5 ± 2.7^**	-11.8 ± 1.4^**	-1.7 ± 1.5	-35.9 ± 2.5^**	-4.6 ± 0.6^**
2020	0.30 ± 0.03^**	0.51 ± 0.01^**	-89.8 ± 2.7^**	-25.8 ± 1.4^**	-17 ± 1.5^**	-44.9 ± 2.5^**	-4.4 ± 0.6^**
物种剔除影响 Effect of species removal
变异解释 Variability (%)	39.8%	9.7%	1.90%	22.3%	52.6%	32.1%	28.3%
F	24.1^**	3.7^**	1.62^*	12.7^**	29.6	23.4^**	9.2^**
自由度 df	20	20	20	20	20	20	20
影响效应 Effect size (与对照比, 各处理的影响以斜率均值 ± 标准差度量 Effect size of treatment vs. CK was measured by mean ± SD of slopes)
剔除优势嵩草 K_sp	-0.05 ± 0.03	-0.11 ± 0.01^**	-5.4 ± 3.3	-11.4 ± 1.8^**	-1.7 ± 1.8	-4.8 ± 3.1	-0.5 ± 0.7
剔除禾草物种 G_sp	-0.20 ± 0.03^**	-0.11 ± 0.01^**	-7.70 ± 3.3^*	-0.36 ± 1.8	-14.4 ± 1.9^**	7.8 ± 3.1^*	-0.5 ± 0.7
剔除杂类草物种 F_sp	-0.45 ± 0.04^**	-0.30 ± 0.01^**	-8.0 ± 3.3^*	6.0 ± 1.8^**	19.2 ± 1.9^**	-31.1 ± 3.1^**	5.7 ± 0.7^**
剔除豆科物种 L_sp	-0.07 ± 0.03^*	-0.09 ± 0.01^**	-7.6 ± 3.3^*	-0.42 ± 1.8	-0.5 ± 1.8	-4.7 ± 3.1	-2.3 ± 0.8^**
各功能群部分物种剔除 P_sp	-0.11 ± 0.03^**	-0.19 ± 0.01^**	-3.7 ± 3.3	-3.8 ± 1.7^*	-2.7 ± 1.8	-1.7 ± 3.1	1.1 ± 0.7
残差 Residuals
变异解释 Variability (%)	25.7%	40.5%	18.2%	26.9%	27.2%	21.2%	45.0%
自由度 df	312	312	312	306	306	308	292

图2 利用广义线性混合模型分析评估高寒草甸植物群落属性对草原毛虫数量的影响。将观测年月作为随机因子, 广义线性混合模型中植物群落属性(因变量)的斜率及置信区间表示了植物群落总的地上生物量、个体数及物种数对草原毛虫数量的影响效应(a-e), 以及各功能群的生物量(f-j)、个体数(k-o)和物种数量(p-t)对草原毛虫数量(每月第1-4次观测以及多次观测中位数)的影响, 其中带*的蓝或红色斜率值及置信区间(不与零相交)表示显著的(* P < 0.05, ** P < 0.001, 加粗为边缘显著0.05 < P < 0.1)正或负影响效应, 不带*的斜率值为不显著(置信区间与零相交)。

Fig. 2 Effect of plant community attributes on numbers of grassland caterpillar in a Tibetan alpine meadow assessed by generalized linear mixed models (GLMM). Using difference in years and month as random factors, the values and 95% confidence interval (CI) of estimated slopes from GLMM measured the effect of whole community attributes (aboveground biomass, individual numbers and species numbers) on caterpillar counts (a-e), aboveground biomass (f-j), individual numbers (k-o), and species numbers (p-t) of each functional groups on the caterpillar counts, with significant positive (blue) and negative (red) effect highlighted by values with * and CI (not overlap with zero) of the estimated slopes (* P < 0.05, ** P < 0.01, no * but bolded values indicates 0.05 < P < 0.1), and the values without * and CI (not overlap zero) indicated non-significant effect.

图3 结构方程模型揭示高寒植物物种剔除通过改变群落属性和结构影响草原毛虫数量。以年份和月份作为随机因子, 结构方程模型中各物种剔除处理对群落中各植物功能群多度以及后者对毛虫数量的显著正、负影响用带正、负数字的蓝色、红色单箭头线表示(粗细根据斜率数值表示影响大小); 不显著的影响途径未标明; 灰色的双箭头表示中间介导变量间有相关性。R2c表示整合随机影响的植物物种剔除处理对植物群落属性的解释量及植物群落属性对草原毛虫数量的解释量; 总体模型拟合参数为: Fisher’s C = 16.2, P = 0.09, df = 10。

Fig. 3 Structural equation model (SEM) revealed the effect of plant species removal in the alpine meadow on caterpillar counts mostly via change in attribute and structure of plant communities. Using difference in year and month as random factors, the estimated slopes in SEM measured effect of plant species removal on plant community as well as plant community on caterpillar counts, with blue and red single-arrowed lines accompanying values with * indicate significant (* P < 0.05, ** P < 0.01, no * 0.05 < P < 0.1) positive and negative effect (the width of lines corresponding to the values that indicate strength of the effect), respectively; gray double-arrowed lines for correlations between variables of plant community. R2c indicates explanation of plant removal treatment on variables of plant community and later to Caterpillar numbers. Global goodness-of-fit: Fisher’s C = 16.2, P = 0.09, df = 10.

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