Ecological mechanisms regulating the dynamics of the field rotifer population in a subtropical lake: evidence from the density, reproduction, and morphology of a case rotifer, Brachionus angularis

Figures & data

Figure 1. Annual dynamics of two fractions of Chl-a (Chl-a and Chl-a < 25 μm) in Lake Tingtang (Wen et al.,2017). The dotted and solid arrows indicate the variation trends of two fractions of Chl-a in March and April 2009, respectively.

Figure 2. Principal component analyses of the environmental factors measured in this study. a: winter and spring; b: summer and autumn.

Figure 3. Annual dynamics of potential competitors and predators of B. angularis in Lake Tingtang. The dotted and arrows indicate the density dynamics of zooplankton in March and April 2009, respectively.

Figure 4. Dynamics of population density, egg ratio, and mixis rate of the B. angularis population in Lake Tingtang. The dotted and solid arrows indicate the density dynamics of the B. angularis population in March and April 2009, respectively.

Figure 5. Regression relationships between density and egg ratio of the B. angularis population and water temperature during summer and autumn. The population density was ln (X + 1) transformed.

Table 1. The Pearson correlation coefficients between population density and egg ratio of B. angularis and environmental factors in Lake Tingtang. (The densities of the zooplankton listed in the table were ln (X + 1) transformed; *p < 0.05; **p < 0.01).

Factors	Winter and Spring		Summer and Autumn		Year-round data that included those in May and November
	Egg ratio	Density	Egg ratio	Density	Egg ratio	Density
Egg ratio	−	−0.48*	−	0.16	−	−0.17
Water temperature (°C)	0.05	0.13	0.51*	0.52*	0.13	−0.05
Secchi-disk depth (m)	−0.66**	0.17	−0.16	0.22	−0.42**	0.14
Dissolved Oxygen (mg.L^−1)	−	−	0.36	−0.25	0.16	−0.19
Chl-a < 25 μm (µg.L^−1)	0.56*	−0.13	0.18	−0.24	0.35*	−0.17
Chl-a concentration (µg.L^−1)	0.55*	−0.16	0.12	−0.15	0.33*	−0.16
Bosmina spp. (ind.L^−1)	−0.45	0.28	0.12	−	−0.22	0.18
Diaphanosoma spp. (ind.L^−1)	−	−	0.15	0.60**	0.16	0.15
Cyclopoida copepod (ind.L^−1)	−0.03	0.16	0.06	0.55*	0.12	0.21
Nauplius ( ind.L^−1)	0.06	0.12	0.19	0.43	0.13	0.19
Asplanchna spp. ( ind.L^−1)	0.44	−0.16	0.41	0.77**	0.23	−0.11
Guild (ind.L^−1)	−0.66**	0.81**	0.36	0.75**	0.003	0.80**

Figure 6. Regression relationships between egg ratio of the B. angularis population and Secchi-disk depth (a), Chl-a < 25 μm (b) and population density of B. angularis (c and d) during winter and spring. The population density in C and D was ln (X + 1) transformed and the values obtained in January 2010 when a density peak occurred were ignored in D.

Table 2. Forward stepwise regression analyses between dependent variables of egg ratio (Y₁: year-round data; Y₂: winter and spring population), body size (Y₃), and egg volume (Y₄) and independent variables of environmental factors.

	Full model	R^2	p	Standardized coefficient
Egg ratio	Y1 = –0.005XSD + 0.88	0.18	<0.01	βSD = –0.42**
Egg ratio	Y2 = –0.01XSD + 1.30	0.41	<0.01	βSD = –0.66**
Body size	Y3 = (–1.64XWT + 4.78XNau + 0.078XSD + 48.82) × 10^4	0.86	<0.001	βWT = –1.05** βNau = 0.29**, βSD = 0.17**
Egg volume	Y4 = (–0.43XWT + 0.054XSD + 18.32) × 10^4	0.88	<0.001	βWT = –0.71** βSD = 0.31**

WT: water temperature; SD: Secchi-disk depth; Nau: Nauplii.

Figure 7. Regression relationships between body size and egg volume of B. angularis and water temperature in Lake Tingtang.

Table 3. The Pearson correlation coefficients between body size and egg volume of B. angularis and environmental factors in Lake Tingtang. (The densities of the zooplankton listed in the table were ln (X + 1) transformed; *p < 0.05; **p < 0.01).

Environmental factor	Body size	Egg volume
Water temperature (°C)	–0.90**	–0.91**
Secchi-disk depth (m)	0.63**	0.76**
Dissolved Oxygen (mg.L^–1)	0.51**	0.48**
Chl-a < 25 μm (µg.L^–1)	–0.48**	–0.51**
Chl-a concentration (µg.L^–1)	–0.47**	–0.52**
Bosmina sp. (ind.L^–1)	0.14	0.28*
Diaphanosoma sp. ( ind.L^–1)	–0.63**	–0.63**
Cyclopoida ( ind.L^–1)	–0.73**	–0.64**
Nauplius ( ind.L^–1)	–0.68**	–0.67**
Asplanchna sp. ( ind.L^–1)	–0.81**	–0.81**
Feeding guild ( ind.L^–1)	0.41**	0.47**

Wen XL, Xi YL, Zhang G, Xue YH, Xiang XL. 2016. Coexistence of cryptic Brachionus calyciflorus (Rotifera) species: roles of environmental variables. J Plankton Res. 38(3):478–489.

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