Ecological Archives E087-167-A5

**Selene Báez, Scott L. Collins, David Lightfoot, and Terri L. Koontz. 2006. Bottom-up regulation of plant community structure in an aridland ecosystem. Ecology 87:2746–2754.**

Appendix E. Analysis of covariance (ANCOVA) of cover and species richness of grass- and shrub-dominated vegetation in control and treatment plots in response to seasonal rainfall. Tr = treatment, Ps = summer precipitation, Pw = winter precipitation. In statistically significant models, significant P values for precipitation and treatment effects are presented in bold.

Shrub vegetation: cover vs. summer precipitation
	ANOVA						Parameter estimates
	Source	df	SS	MS	F	P	Term	Estimate	Std. Error	P
Summer annuals	R² = 0.053						Intercept	0.175	0.080	0.031
	Model	3	0.334	0.111	1.429	0.241	Tr	-0.024	0.031	0.447
	Error	76	5.917	0.078			Ps	0.001	0.001	0.076
	C. Total	79	6.251				Tr × Ps	0.000	0.001	0.495
Forbs	R² = 0.03						Intercept	0.046	0.137	0.738
	Model	3	0.581	0.194	0.861	0.465	Tr	-0.019	0.053	0.724
	Error	75	16.865	0.225			Ps	0.001	0.001	0.248
	C. Total	78	17.446				Tr × Ps	0.001	0.001	0.290
Grasses	R² = 0.09						Intercept	0.635	0.079	<0.001
	Model	3	0.593	0.198	2.573	0.060	Tr	-0.074	0.031	0.019
	Error	76	5.836	0.077			Ps	0.001	0.001	0.160
	C. Total	79	6.429				Tr × Ps	0.000	0.001	0.977
Shrubs	R² = 0.07						Intercept	1.463	0.036	<0.001
	Model	3	0.084	0.028	1.834	0.148	Tr	0.032	0.014	0.025
	Error	75	1.149	0.015			Ps	0.000	0.000	0.629
	C. Total	78	1.234				Tr × Ps	0.000	0.000	0.934
Total	R² = 0.04						Intercept	1.406	0.038	<0.001
	Model	3	0.057	0.019	1.078	0.364	Tr	0.017	0.015	0.268
	Error	75	1.316	0.018			Ps	0.000	0.000	0.170
	C. Total	78	1.372				Tr × Ps	0.000	0.000	0.844
Heterogeneity	R² = 0.11						Intercept	3.699	0.066	<0.001
	Model	3	0.484	0.161	3.014	0.035	Tr	0.076	0.026	0.004
	Error	76	4.072	0.054			Ps	0.000	0.000	0.589
	C. Total	79	4.556				Tr × Ps	0.000	0.000	0.842
Shrub vegetation: cover vs. winter precipitation
Winter annuals	R² = 0.43						Intercept	-0.060	0.048	0.213
	Model	3	2.039	0.680	19.234	<0.001	Tr	0.028	0.021	0.180
	Error	76	2.686	0.035			Pw	0.003	0.000	<0.001
	C. Total	79	4.725				Tr × Pw	0.001	0.000	0.086
Forbs	R² = 0.045						Intercept	0.045	0.120	0.709
	Model	3	0.692	0.231	1.032	0.383	Tr	-0.019	0.053	0.728
	Error	75	16.755	0.223			Pw	0.001	0.001	0.174
	C. Total	78	17.446				Tr × Pw	0.001	0.001	0.297
Grasses	R² = 0.11						Intercept	0.628	0.070	<0.001
	Model	3	0.686	0.229	3.024	0.035	Tr	-0.074	0.031	0.019
	Error	76	5.743	0.076			Pw	0.001	0.001	0.082
	C. Total	79	6.429				Tr × Pw	0.000	0.001	0.686
Shrubs	R² = 0.07						Intercept	1.492	0.032	<0.001
	Model	3	0.085	0.028	1.844	0.146	Tr	0.032	0.014	0.025
	Error	75	1.149	0.015			Pw	0.000	0.000	0.643
	C. Total	78	1.234				Tr × Pw	0.000	0.000	0.823
Total	R² = 0.03						Intercept	1.453	0.034	<0.001
	Model	3	0.036	0.012	0.683	0.566	Tr	0.017	0.015	0.267
	Error	75	1.336	0.018			Pw	0.000	0.000	0.959
	C. Total	78	1.372				Tr × Pw	0.000	0.000	0.375
Heterogeneity	R² = 0.21						Intercept	3.889	0.055	<0.001
	Model	3	0.941	0.314	6.592	0.001	Tr	0.076	0.024	0.003
	Error	76	3.615	0.048			Pw	-0.002	0.000	0.002
	C. Total	79	4.556				Tr × Pw	0.000	0.000	0.814
Shrub vegetation: species richness vs. summer precipitation
Summer annuals	R² = 0.025						Intercept	0.149	0.029	<0.001
	Model	3	0.020	0.007	0.648	0.587	Tr	0.007	0.011	0.546
	Error	76	0.797	0.010			Ps	0.000	0.000	0.216
	C. Total	79	0.817				Tr × Ps	0.000	0.000	0.883
Forbs	R² < 0.01						Intercept	1.348	0.247	<0.001
	Model	3	0.117	0.039	0.052	0.984	Tr	0.030	0.097	0.754
	Error	76	56.692	0.746			Ps	0.000	0.002	0.855
	C. Total	79	56.808				Tr × Ps	0.000	0.002	0.877
Grasses	R² = 0.03						Intercept	0.844	0.097	<0.001
	Model	3	0.268	0.089	0.774	0.512	Tr	-0.044	0.038	0.249
	Error	76	8.754	0.115			Ps	0.001	0.001	0.354
	C. Total	79	9.021				Tr × Ps	0.000	0.001	0.752
Shrubs	R² = <0.01						Intercept	0.889	0.065	<0.001
	Model	3	0.031	0.010	0.200	0.896	Tr	-0.014	0.025	0.577
	Error	76	3.880	0.051			Ps	0.000	0.000	0.664
	C. Total	79	3.911				Tr × Ps	0.000	0.000	0.757
Total	R² < 0.01						Intercept	3.081	0.281	<0.001
	Model	3	0.138	0.046	0.047	0.986	Tr	-0.028	0.110	0.800
	Error	76	73.499	0.967			Ps	0.001	0.002	0.795
	C. Total	79	73.637				Tr × Ps	0.000	0.002	0.922
Shrub vegetation: species richness vs. winter rainfall
Winter annuals	R² = 0.43						Intercept	-0.060	0.048	0.213
	Model	3	2.039	0.680	19.234	<0.001	Tr	0.028	0.021	0.180
	Error	76	2.686	0.035			Pw	0.003	0.000	<0.001
	C. Total	79	4.725				Tr × Pw	0.001	0.000	0.086
Forbs	R² = 0.21						Intercept	0.528	0.195	0.009
	Model	3	11.835	3.945	6.666	0.001	Tr	0.030	0.086	0.725
	Error	76	44.974	0.592			Pw	0.008	0.002	<0.001
	C. Total	79	56.808				Tr × Pw	0.001	0.002	0.739
Grasses	R² = 0.02						Intercept	0.935	0.087	<0.001
	Model	3	0.173	0.058	0.495	0.687	Tr	-0.044	0.038	0.251
	Error	76	8.849	0.116			Pw	0.000	0.001	0.918
	C. Total	79	9.021				Tr × Pw	0.000	0.001	0.713
Shrubs	R² = 0.04						Intercept	0.826	0.056	<0.001
	Model	3	0.173	0.058	1.173	0.326	Tr	-0.014	0.025	0.570
	Error	76	3.738	0.049			Pw	0.001	0.001	0.080
	C. Total	79	3.911				Tr × Pw	0.000	0.001	0.827
Total	R² = 0.19	0.19					Intercept	2.289	0.224	<0.001
	Model	3	14.342	4.781	6.127	0.001	Tr	-0.028	0.099	0.778
	Error	76	59.295	0.780			Pw	0.009	0.002	<0.001
	C. Total	79	73.637				Tr × Pw	0.000	0.002	0.926
Grass vegetation: cover vs. summer precipitation
Summer annuals	R² = 0.27						Intercept	-0.029	0.111	0.796
	Model	3	4.478	1.493	9.259	<0.001	Tr	0.035	0.045	0.433
	Error	76	12.253	0.161			Ps	0.003	0.001	<0.001
	C. Total	79	16.731				Tr × Ps	0.000	0.001	0.589
Forbs	R² = 0.18						Intercept	-0.143	0.151	0.349
	Model	3	5.062	1.687	5.611	0.002	Tr	-0.002	0.061	0.969
	Error	76	22.855	0.301			Ps	0.004	0.001	0.000
	C. Total	79	27.917				Tr × Ps	0.000	0.001	0.935
Grasses	R² = 0.19						Intercept	1.420	0.030	<0.001
	Model	3	0.210	0.070	5.941	0.001	Tr	0.007	0.012	0.549
	Error	76	0.897	0.012			Ps	0.001	0.000	<0.001
	C. Total	79	1.107				Tr × Ps	0.000	0.000	0.887
Shrubs	R² = 0.07						Intercept	0.410	0.094	<0.001
	Model	3	0.623	0.208	1.806	0.153	Tr	-0.086	0.038	0.027
	Error	76	8.745	0.115			Ps	0.000	0.001	0.819
	C. Total	79	9.369				Tr × Ps	0.000	0.001	0.617
Total	R² = 0.28						Intercept	1.447	0.034