Small mammalian herbivores at moderate densities facilitate livestock growth by improving vegetation composition in grasslands
- Key Laboratory of Vegetation Ecology of the Ministry of Education, Songnen Grassland Ecosystem National Observation and Research Station, Northeast Normal University, China
- Key Laboratory of Marsh Wetland Ecosystem Conservation and Restoration, National Forestry and Grassland Administration, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, China
- Qinghai Provincial Key Laboratory of Cold Regions Restoration Ecology, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, China
- School of Sustainability, Arizona State University, United States
- College of Resources and Environmental Sciences, Key Laboratory of Sustainable Utilization of Soil Resources in the Commodity Grain Bases in Jilin Province, Jilin Agricultural University, China
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, China
- State Key Laboratory of Herbage Improvement and Grassland Agro-Ecosystems, College of Ecology, Lanzhou University, China
- China-Kazakhstan Belt and Road Joint Laboratory on Grassland Ecological Restoration, College of Pastoral Agriculture Science and Technology, Lanzhou University, China
- Key Laboratory of Alpine Grassland Ecosystem in the Three-River-Source, Ministry of Education/Qinghai Provincial Key Laboratory of Adaptive Management on Alpine Grassland, Qinghai University, China
- School of Grassland Science, Beijing Forestry University, China
- School of Life and Environmental Sciences, The University of Sydney, Australia
- Center for Ecological Dynamics in a Novel Biosphere (ECONOVO), Department of Biology, Aarhus University, Ny Munkegade, Denmark
- School of Ecology, Hainan International One Health Institute, Hainan Province Key Laboratory of One Health, Hainan University, China
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Chaoyang District, China
Figures
Figure 1
Conceptual diagram of the hypothesized facilitative effects of pikas (Ochotona curzoniae) on yak (Bos grunniens) growth performance on the Qinghai–Tibetan Plateau.
(A) In the absence of pikas, the poisonous forb Stellera chamaejasme exerts strong negative effects on the growth of yaks by outcompeting palatable grasses and sedges, thereby reducing forage availability and foraging efficiency. (B) In the presence of pikas, clipping of Stellera suppresses its abundance, mitigating its negative impact and promoting yak growth. Gray dashed line and ‘+’ indicate livestock grazing promotes the proliferation of the poisonous forbs by suppressing palatable grasses and sedges. Black dashed lines indicate negative effects of poisonous plants on yaks, black solid lines indicate competition between plant groups, and red solid lines indicate pika suppression of Stellera. Line thickness represents the relative strength of putative species interactions. (C, D) show pika clipping activity and its effect on Stellera abundance at the study site. Credits: Xiaona Zheng (photographs).
Figure 2
Diet selection of pikas and yaks and their potential interactions mediated by poisonous plants based on field surveys in July 2021.
(A) Feeding and clipping frequencies of pikas, and (B) grazing frequencies of yaks on grasses, sedges, forbs, and Stellera across 10 2×2 m plots and 10 250 m transects, respectively. (C) Relationship between active pika burrow density and Stellera cover, and (D) between Stellera cover and an index of yak grazing activity (dung density) in 30 10×10 m plots. (E) Photographs showing (left to right) a pika at its burrow entrance, flowering Stellera, and a yak grazing among Stellera plants. Different letters above bars indicate significant differences at p<0.05. Credits: Xiaona Zheng (photographs).
Figure 3
Combined effects of two-year (2022–2023) pika and Stellera removal treatments on yak growth, forage quantity, and quality in the field manipulative experiment.
(A) Pika density (indicated by active burrow density), (B) yak weight gain, (C) relationship between pika density and yak weight gain, (D) Stellera cover, (E) grass cover, (F) sedge cover, (G) crude protein (CP) content, (H) acid detergent fiber (ADF) content, and (I) neutral detergent fiber (NDF) of total forage (dry mass basis). Average values from both years were used in analyses, yielding one data point per 150×150 m plot. Significant interactions between pikas and Stellera were evaluated using post hoc tests; means not sharing letters differ significantly. For panels (A) and (F), only main effects were significant (Appendix 1—table 5). Error bars indicate ±SE.
Figure 4
Combined effects of two-year (2022–2023) pika and Stellera removal treatments on yak foraging efficiency in the field manipulative experiment.
(A, B) Bite rates and (C, D) bites per step for sedges and grasses, respectively. Mean values from both years were used for analysis (one data point per 150×150 m plot). Significant interactions between pikas and Stellera were evaluated using post hoc tests; means not sharing letters differ significantly. Error bars indicate ±SE.
Appendix 1—figure 1
Combined effects of two-year (2022–2023) pika and Stellera removal on forb cover in the field manipulative experiment.
The average values of each variable in the two years were used for statistical analysis, providing a single data point for each variable in each 150×150 m plot. Error bars represent ±SE.
Appendix 1—figure 2
Combined effects of two-year (2022–2023) pika and Stellera removal on foraging efficiency of yaks in the field manipulative experiment.
(A) Bite rates and (B) bites per step of yaks for forbs, respectively. The average values of each variable in the two years were used for statistical analysis, providing a single data point for each variable in each 150×150 m plot. Error bars represent ±SE.
Tables
Appendix 1—table 1
Model summary for diet and clipping selections of pikas and yaks in the field surveys in July 2021.
| Effect | Term | Estimate | SE | Statistic | P |
|---|---|---|---|---|---|
| Pika feeding/clipping | |||||
| Fixed | (Intercept) | 36.33 | 3.24 | 11.23 | <0.001 |
| Fixed | Grasses | –21.67 | 4.39 | –4.94 | <0.001 |
| Fixed | Stellera | 23.67 | 4.39 | 5.39 | <0.001 |
| Fixed | Sedges | –18.67 | 4.39 | –4.25 | <0.001 |
| Random | Plot | <0.001 | NA | NA | NA |
| Random | Month | 1.58 | NA | NA | NA |
| Random | Residual | 17.00 | NA | NA | NA |
| Yak grazing | |||||
| Fixed | (Intercept) | 16.33 | 3.23 | 5.05 | <0.001 |
| Fixed | Grasses | 58.00 | 4.24 | 13.68 | <0.001 |
| Fixed | Sedges | 29.00 | 4.24 | 6.84 | <0.001 |
| Random | Transect | 3.83 | NA | NA | NA |
| Random | Month | <0.001 | NA | NA | NA |
| Random | Residual | 16.42 | NA | NA | NA |
Appendix 1—table 2
Model contrasts for diet and clipping selections of pikas and yaks in the field surveys in July 2021.
| Contrast | Estimate | SE | df | t ratio | P |
|---|---|---|---|---|---|
| Pika feeding/clipping | |||||
| Forbs−Grasses | 21.67 | 4.39 | 113.00 | 4.94 | <0.001 |
| Forbs−Stellera | –23.67 | 4.39 | 113.00 | –5.39 | <0.001 |
| Forbs−Sedges | 18.67 | 4.39 | 113.00 | 4.25 | <0.001 |
| Grasses−Stellera | –45.33 | 4.39 | 113.00 | –10.33 | <0.001 |
| Grasses−Sedges | –3.00 | 4.39 | 113.00 | –0.68 | 0.90 |
| Stellera−Sedges | 42.33 | 4.39 | 113.00 | 9.64 | <0.001 |
| Yak grazing | |||||
| Forbs−Grasses | –58.00 | 4.24 | 84.00 | –13.68 | <0.001 |
| Forbs−Sedges | –29.00 | 4.24 | 84.00 | –6.84 | <0.001 |
| Grasses−Sedges | 29.00 | 4.24 | 84.00 | 6.84 | <0.001 |
Appendix 1—table 3
Model summary for Stellera cover regressed on active pika burrow density.
Estimates are from a generalized additive mixed model (Gaussian family) with plot as a random effect (n=30 plots).
| Term | Estimate | SE | Statistic | P | edf | ref.df |
|---|---|---|---|---|---|---|
| Intercept | 13.33 | 1.21 | 10.99 | <0.00 | NA | NA |
| Active pika burrow density | NA | NA | 13.17 | <0.00 | 2.10 | 7.00 |
| Plot | NA | NA | 1.17 | 0.06 | 15.12 | 29.00 |
Appendix 1—table 4
Model summary for yak dung density regressed on Stellera cover.
Estimates are from a linear regression model (n=30 plots).
| Term | Estimate | SE | Statistic | P |
|---|---|---|---|---|
| Intercept | 19.07 | 1.41 | 13.50 | <0.00 |
| Stellera cover | −0.42 | 0.09 | −4.62 | <0.00 |
Appendix 1—table 5
Model summary for interactive effects of pikas and Stellera on pika burrow density, yak weight gain, Stellera cover, grass cover, sedge cover, and forb cover in the field manipulative experiment in 2022–2023.
| Effect | Term | Estimate | SE | Statistic | P |
|---|---|---|---|---|---|
| Pika burrow density | |||||
| Fixed | (Intercept) | 20.21 | 17.10 | 1.18 | 0.24 |
| Fixed | Pika | 149.67 | 22.01 | 6.80 | <0.001 |
| Fixed | Stellera | −2.42 | 22.01 | −0.11 | 0.91 |
| Fixed | Pika×Stellera | 28.42 | 31.13 | 0.91 | 0.36 |
| Random | Block | 14.20 | NA | NA | NA |
| Random | Month | <0.001 | NA | NA | NA |
| Random | Residual | 76.24 | NA | NA | NA |
| Yak weight gain | |||||
| Fixed | (Intercept) | 0.32 | 0.03 | 10.80 | <0.001 |
| Fixed | Pika | 0.01 | 0.01 | 0.74 | 0.46 |
| Fixed | Stellera | −0.11 | 0.01 | −7.70 | <0.001 |
| Fixed | Pika×Stellera | 0.13 | 0.02 | 6.63 | <0.001 |
| Random | Block | 0.01 | NA | NA | NA |
| Random | Year | 0.01 | NA | NA | NA |
| Random | Month | 0.05 | NA | NA | NA |
| Stellera cover | |||||
| Fixed | (Intercept) | −3.44 | 0.26 | −13.39 | <0.001 |
| Fixed | Pika | −0.11 | 0.22 | −0.49 | 0.62 |
| Fixed | Stellera | 2.25 | 0.17 | 12.91 | <0.001 |
| Fixed | Pika×Stellera | −1.15 | 0.25 | −4.58 | <0.001 |
| Random | Block | 0.16 | NA | NA | NA |
| Random | Year | 0.17 | NA | NA | NA |
| Random | Month | 0.24 | NA | NA | NA |
| Grass cover | |||||
| Fixed | (Intercept) | −1.11 | 0.10 | −11.58 | <0.001 |
| Fixed | Pika | −0.09 | 0.10 | −0.90 | 0.37 |
| Fixed | Stellera | −0.88 | 0.11 | −7.76 | <0.001 |
| Fixed | Pika×Stellera | 0.90 | 0.15 | 5.97 | <0.001 |
| Random | Block | 0.13 | NA | NA | NA |
| Random | Year | <0.001 | NA | NA | NA |
| Random | Month | 0.02 | NA | NA | NA |
| Sedge cover | |||||
| Fixed | (Intercept) | 0.02 | 0.08 | 0.32 | 0.75 |
| Fixed | Pika | 0.12 | 0.08 | 1.50 | 0.13 |
| Fixed | Stellera | −0.27 | 0.08 | −3.51 | <0.001 |
| Fixed | Pika×Stellera | 0.19 | 0.11 | 1.77 | 0.08 |
| Random | Block | 0.08 | NA | NA | NA |
| Random | Year | <0.001 | NA | NA | NA |
| Random | Month | 0.06 | NA | NA | NA |
| Forb cover | |||||
| Fixed | (Intercept) | −1.12 | 0.11 | −10.56 | <0.001 |
| Fixed | Pika | 0.05 | 0.10 | 0.50 | 0.62 |
| Fixed | Stellera | −0.22 | 0.10 | −2.21 | 0.03 |
| Fixed | Pika×Stellera | 0.09 | 0.14 | 0.65 | 0.52 |
| Random | Block | 0.10 | NA | NA | NA |
| Random | Year | 0.09 | NA | NA | NA |
| Random | Month | <0.001 | NA | NA | NA |
Appendix 1—table 6
Model contrasts for yak weight gain, Stellera cover, and grass cover in the field manipulative experiment in 2022–2023.
| Contrast | Estimate | SE | df | t ratio | P |
|---|---|---|---|---|---|
| Yak weight gain | |||||
| No pika+No Stellera− Pika+No Stellera | −0.01 | 0.01 | 184.00 | −0.74 | 0.88 |
| No pika+No Stellera− No pika+Stellera | 0.11 | 0.01 | 184.00 | 7.70 | <0.001 |
| No pika+No Stellera− Pika+Stellera | −0.03 | 0.01 | 184.00 | −2.42 | 0.08 |
| Pika+No Stellera− No pika+Stellera | 0.12 | 0.01 | 184.00 | 8.44 | <0.001 |
| Pika+No Stellera− Pika+Stellera | −0.02 | 0.01 | 184.00 | −1.68 | 0.34 |
| No pika+Stellera− Pika+Stellera | −0.14 | 0.01 | 184.00 | −10.12 | <0.001 |
| Stellera cover | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.24 | Inf | NA | 0.96 |
| No pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.07 | Inf | NA | <0.001 |
| Pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.06 | Inf | NA | <0.001 |
| No pika+Stellera− Pika+Stellera | NA | 0.46 | Inf | NA | <0.001 |
| Grass cover | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.11 | Inf | NA | 0.81 |
| No pika+No Stellera− No pika+Stellera | NA | 0.27 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.11 | Inf | NA | 0.90 |
| Pika+No Stellera− No pika+Stellera | NA | 0.25 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.10 | Inf | NA | 1.00 |
| No pika+Stellera− Pika+Stellera | NA | 0.05 | Inf | NA | <0.001 |
Appendix 1—table 7
Model summary for yak weight gain regressed on active burrow count in plots with both pika presence and Stellera presence.
Estimates are from a generalized additive mixed model (Gaussian family) with a non-linear smooth for active burrows, block, year, and month as random effects (n=24 observations from the pika+Stellera treatment).
| Term | edf | ref.df | Statistic | P |
|---|---|---|---|---|
| Active burrows | 2.27 | 14.00 | 4.74 | <0.001 |
| Block | 1.72 | 3.00 | 1.44 | 0.09 |
| Year | 0.23 | 1.00 | 0.31 | 0.25 |
| Month | 1.57 | 2.00 | 5.24 | 0.01 |
Appendix 1—table 8
Model summary for interactive effects of pikas and Stellera on crude protein (CP) %, acid detergent fiber (ADF) %, and neutral detergent fiber (NDF) % of total forage in the field manipulative experiment in 2022–2023.
| Effect | Term | Estimate | SE | Statistic | P |
|---|---|---|---|---|---|
| CP | |||||
| Fixed | (Intercept) | −2.39 | 0.02 | −107.03 | <0.001 |
| Fixed | Pika | 0.03 | 0.02 | 1.88 | 0.06 |
| Fixed | Stellera | −0.15 | 0.02 | −8.72 | <0.001 |
| Fixed | Pika×Stellera | 0.13 | 0.02 | 5.45 | <0.001 |
| Random | Block | 0.01 | NA | NA | NA |
| Random | Year | <0.001 | NA | NA | NA |
| Random | Month | 0.03 | NA | NA | NA |
| ADF | |||||
| Fixed | (Intercept) | −0.82 | 0.03 | −32.36 | <0.001 |
| Fixed | Pika | 0.01 | 0.02 | 0.46 | 0.65 |
| Fixed | Stellera | −0.06 | 0.02 | −3.14 | <0.001 |
| Fixed | Pika×Stellera | 0.08 | 0.03 | 2.84 | <0.001 |
| Random | Block | 0.03 | NA | NA | NA |
| Random | Year | <0.001 | NA | NA | NA |
| Random | Month | 0.03 | NA | NA | NA |
| NDF | |||||
| Fixed | (Intercept) | 0.51 | 0.02 | 27.44 | <0.001 |
| Fixed | Pika | 0.03 | 0.03 | 1.03 | 0.30 |
| Fixed | Stellera | −0.05 | 0.02 | −2.03 | 0.04 |
| Fixed | Pika×Stellera | 0.02 | 0.04 | 0.61 | 0.54 |
| Random | Block | 0.01 | NA | NA | NA |
| Random | Year | <0.001 | NA | NA | NA |
| Random | Month | <0.001 | NA | NA | NA |
Appendix 1—table 9
Model contrasts for crude protein (CP) % and acid detergent fiber (ADF) % of total forage in the field manipulative experiment in 2022–2023.
| Contrast | Estimate | SE | df | t ratio | P |
|---|---|---|---|---|---|
| CP | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.02 | Inf | NA | 0.24 |
| No pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.02 | Inf | NA | 0.91 |
| Pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.02 | Inf | NA | 0.61 |
| No pika+Stellera− Pika+Stellera | NA | 0.01 | Inf | NA | <0.001 |
| ADF | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.02 | Inf | NA | 0.97 |
| No pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.02 | Inf | NA | 0.54 |
| Pika+No Stellera− No pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.02 | Inf | NA | 0.82 |
| No pika+Stellera− Pika+Stellera | NA | 0.02 | Inf | NA | <0.001 |
Appendix 1—table 10
Model summary for interactive effects of pikas and Stellera on yak bite rate (bites/hr) and the bite to step ratio (bites/step) for grasses, sedges, and forbs in the field manipulative experiment in 2022–2023.
| Effect | Term | Estimate | SE | Statistic | P |
|---|---|---|---|---|---|
| Grass bites/h | |||||
| Fixed | (Intercept) | 151.72 | 7.49 | 20.25 | <0.001 |
| Fixed | Pika | −0.80 | 8.61 | −0.09 | 0.93 |
| Fixed | Stellera | −45.34 | 8.61 | −5.27 | <0.001 |
| Fixed | Pika×Stellera | 43.95 | 12.17 | 3.61 | <0.001 |
| Random | Block | 4.78 | NA | NA | NA |
| Random | Year | 5.17 | NA | NA | NA |
| Random | Month | 0.00 | NA | NA | NA |
| Random | Residual | 42.16 | NA | NA | NA |
| Sedge bites/h | |||||
| Fixed | (Intercept) | 5.65 | 0.04 | 138.78 | <0.001 |
| Fixed | Pika | 0.04 | 0.04 | 0.92 | 0.36 |
| Fixed | Stellera | −0.42 | 0.05 | −8.71 | <0.001 |
| Fixed | Pika×Stellera | 0.35 | 0.06 | 5.51 | <0.001 |
| Random | Block | 0.04 | NA | NA | NA |
| Random | Year | 0.02 | NA | NA | NA |
| Random | Month | 0.03 | NA | NA | NA |
| Forb bites/h | |||||
| Fixed | (Intercept) | 4.39 | 0.07 | 65.12 | <0.001 |
| Fixed | Pika | 0.07 | 0.07 | 1.06 | 0.29 |
| Fixed | Stellera | 0.13 | 0.07 | 1.90 | 0.06 |
| Fixed | Pika×Stellera | −0.04 | 0.10 | −0.44 | 0.66 |
| Random | Block | 0.06 | NA | NA | NA |
| Random | Year | 0.00 | NA | NA | NA |
| Random | Month | 0.05 | NA | NA | NA |
| Grass bites/step | |||||
| Fixed | (Intercept) | −1.01 | 0.08 | −13.16 | <0.001 |
| Fixed | Pika | 0.02 | 0.09 | 0.19 | 0.85 |
| Fixed | Stellera | −0.60 | 0.10 | −6.28 | <0.001 |
| Fixed | Pika×Stellera | 0.67 | 0.13 | 5.15 | <0.001 |
| Random | Block | 0.03 | NA | NA | NA |
| Random | Year | 0.06 | NA | NA | NA |
| Random | Month | 0.00 | NA | NA | NA |
| Sedge bites/step | |||||
| Fixed | (Intercept) | 0.04 | 0.14 | 0.28 | 0.78 |
| Fixed | Pika | 0.08 | 0.12 | 0.67 | 0.50 |
| Fixed | Stellera | −0.95 | 0.12 | −7.61 | <0.001 |
| Fixed | Pika×Stellera | 1.01 | 0.17 | 5.83 | <0.001 |
| Random | Block | 0.17 | NA | NA | NA |
| Random | Year | 0.08 | NA | NA | NA |
| Random | Month | 0.06 | NA | NA | NA |
| Forb bites/step | |||||
| Fixed | (Intercept) | −1.76 | 0.09 | −18.74 | <0.001 |
| Fixed | Pika | 0.06 | 0.09 | 0.64 | 0.52 |
| Fixed | Stellera | −0.05 | 0.09 | −0.49 | 0.63 |
| Fixed | Pika×Stellera | 0.24 | 0.13 | 1.83 | 0.07 |
| Random | Block | 0.11 | NA | NA | NA |
| Random | Year | 0.00 | NA | NA | NA |
| Random | Month | 0.07 | NA | NA | NA |
Appendix 1—table 11
Model contrasts for yak bite rate (bites/hr) and the bite to step ratio (bites/step) on grasses and sedges in the field manipulative experiment in 2022–2023.
| Contrast | Estimate | SE | df | t ratio | P |
|---|---|---|---|---|---|
| Grass bites/hr | |||||
| No pika+No Stellera− Pika +No Stellera | 0.80 | 8.61 | 184.00 | 0.09 | 1.00 |
| No pika+No Stellera− No pika+Stellera | 45.34 | 8.61 | 184.00 | 5.27 | <0.001 |
| No pika+No Stellera− Pika+Stellera | 2.19 | 8.61 | 184.00 | 0.25 | 0.99 |
| Pika+No Stellera− No pika+Stellera | 44.54 | 8.61 | 184.00 | 5.18 | <0.001 |
| Pika+No Stellera− Pika+Stellera | 1.39 | 8.61 | 184.00 | 0.16 | 1.00 |
| No pika+Stellera− Pika+Stellera | −43.15 | 8.61 | 184.00 | −5.01 | <0.001 |
| Sedge bites/h | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.04 | Inf | NA | 0.80 |
| No pika+No Stellera− No pika+Stellera | NA | 0.07 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.04 | Inf | NA | 0.94 |
| Pika+No Stellera− No pika+Stellera | NA | 0.08 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.05 | Inf | NA | 0.45 |
| No pika+Stellera− Pika+Stellera | NA | 0.03 | Inf | NA | <0.001 |
| Grass bites/step | |||||
| No pika +No Stellera− Pika +No Stellera | NA | 0.09 | Inf | NA | 1.00 |
| No pika+No Stellera− No pika+Stellera | NA | 0.17 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.08 | Inf | NA | 0.79 |
| Pika+No Stellera− No pika+Stellera | NA | 0.18 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.08 | Inf | NA | 0.88 |
| No pika+Stellera− Pika+Stellera | NA | 0.05 | Inf | NA | <0.001 |
| Sedge bites/step | |||||
| No pika+No Stellera− Pika+No Stellera | NA | 0.11 | Inf | NA | 0.91 |
| No pika+No Stellera− No pika+Stellera | NA | 0.32 | Inf | NA | <0.001 |
| No pika+No Stellera− Pika+Stellera | NA | 0.10 | Inf | NA | 0.66 |
| Pika+No Stellera− No pika+Stellera | NA | 0.35 | Inf | NA | <0.001 |
| Pika+No Stellera− Pika+Stellera | NA | 0.11 | Inf | NA | 0.96 |
| No pika+Stellera− Pika+Stellera | NA | 0.04 | Inf | NA | <0.001 |
Appendix 1—table 12
Summary statistics from generalized linear mixed effects models testing for pre-treatment differences in response variables representing plant community composition (cover by group) and diversity in designated mesocosm locations, as measured in 2021 prior to initiation of pika presence/absence and Stellera presence/absence treatments.
Appendix 1—table 13
Summary of all statistical models used in the study, including response variables, model type, distribution family (with Tweedie power parameter where applicable), interaction terms, random effects structure, and sample sizes.
All field experiments (2022–2023) used a 2×2 factorial design with pika presence/absence and Stellera presence/absence treatments. GLMM = Generalized Linear Mixed Model; GAM = Generalized Additive Mixed Model; LM = Linear Model. For Tweedie distributions, p indicates the power parameter.
| Statistical models Summary | |||||
|---|---|---|---|---|---|
| Response variable | model type | Distribution/ family | Interaction terms | Random effects | Sample size |
| Diet selection | |||||
| Pika feeding frequency | GLMM | Gaussian | Plot, month | n=10 plots | |
| Yak grazing frequency | GLMM | Gaussian | Transect, month, | n=10 transects | |
| Stellera cover | GAM | Gaussian | plot | n=30 plots | |
| Yak dung density | LM | Gaussian | n=30 plots | ||
| Yak performance | |||||
| Yak weight gain | GLMM | Gaussian | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Yak weight gain (vs burrow density) | GAM | Gaussian | Block, year, month | n=16 plots | |
| Plant cover | |||||
| Grasses | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Sedges | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Forbs | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Stellera | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Active burrow density | GLMM | Gaussian | Pika×Stellera | Block, month | n=16 plots, 2 years |
| Forage quality | |||||
| Crude protein (%) | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Acid detergent fiber (%) | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Neutral detergent fiber (%) | GLMM | Beta | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Foraging efficiency | |||||
| Sedge bite rate | GLMM | Tweedie (p=0.04) | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Grass bite rate | GLMM | Gaussian | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Forb bite rate | GLMM | Tweedie (p=0.07) | Pika×Stellera | Block, year, month | n=16 plots, 2 years |
| Sedge bites/step | GLMM | Beta | Pika×Stellera | Block, month | n=16 plots |
| Grass bites/step | GLMM | Beta | Pika×Stellera | Block, month | n=16 plots |
| Forb bites/step | GLMM | Beta | Pika×Stellera | Block, month | n=16 plots |
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Small mammalian herbivores at moderate densities facilitate livestock growth by improving vegetation composition in grasslands
eLife 15:RP111340.
https://doi.org/10.7554/eLife.111340.3
