Distribution of backswimmers in shallow ponds of Patagonia and their predatory role on a common tadpole–copepod assemblage

Figures & data

Figure 1  Map of the study area (Nahuel Huapi National Park, Patagonia, Argentina). Numbers refer to pond location: 1, Llao-Llao; 2, Fantasma; 3, Virgen de las Nieves; 4, Pinar de Festa; 5, Teleférico; 6, Mallín Ñireco; Ñireco 1 and 2; 7, Los Patos and Verde; 8, Refugio de Jesús; 9, Bernal 1 to 6; 10, Ñirihuau 1 to 4.

Table 1  Environmental features of 21 shallow fishless ponds inside Nahuel Huapi National Park (NHNP, Patagonia, Argentina).

Pond (map reference)	Location	Elevation (m a.s.l)	Landscape unit (proximity to city)	Area (m^2)	Depth (m)	Water regime	Aquatic vegetation	pH, mean (±1SEM)	Conductivity (µS/cm), mean (±1SEM)	Notonectid species	Amphibian species
Llao-Llao (1)	41°2'S; 71°33'W	821	APF (R)	150	0.4	T	*	7.16	NA	1	4, 5, 6
Fantasma (2)	41°5.6'S; 71°27'W	794	APF (U)	10000	2	T	*	7.22 (0.22)	99.86 (6.11)	1	4
Virgen de las Nieves (3)	41°08'S; 71°24'W	801	APF(U)	550	1	P	*	8.39 (0.1)	74.45 (13.22)	1, 2	4
Pinar de Festa (4)	41°0.7'S; 71°21'W	830	APF(U)	13	0.4	T	–	7.11 (0.34)	57.99 (3.68)	–	4, 7
Teleférico (5)	41°7'S, 71°22'W	816	APF (U)	257	1.7	T	*	7.09 (0.17)	183.74 (42.12)	1, 2	4
Mallín Ñireco (6)	41°10'S; 71°19'W	899	S (R)	1000	0.88	P	*	6.6^♦	77.1 (10.9)	1, 2	7, 8
Ñireco 1 (6)	41°10'S; 71°19'W	906	S (R)	240	1.4	T	–	7.8 (0.05)	75.9 (1.97)	–	7
Ñireco 2 (6)	41°10'S; 71°18'W	906	S (R)	<20	0.3	T	–	8.09 (0.32)	85.33 (1.79)	–	7
Los Patos (7)	41°15'S; 71° 17'W	1461	SAF (R)	1010	0.7	P	*	8.02^♦	45.7 (7.49)	3	4, 9
Verde (7)	41°15'S; 71° 17'W	1525	SAF (R)	3540	5	P	–	7.28 (0.62)	28.96 (2.55)	3	9
Refugio de Jesús (8)	41°07'S, 71°13'W	825	S (R)	15000	0.7	T	*	7.46 (0.95)	67.05 (8.64)	1	7
Bernal 1 (9)	41°08'S; 71°11'W	837	S (SU)	556	0.38	T	–	7.82 (0.27)	377.89 (59.82)	–	7
Bernal 2 (9)	41°08’; 71°11'W	837	S (SU)	234	0.45	T	–	7.1 (0.2)	28.30 (5.78)	–	7
Bernal 3 (9)	41°08'S; 71°11'W	838	S (SU)	543	0.46	T	–	7.07 (0.34)	73.94 (27.34)	–	7
Bernal 4 (9)	41°08'S; 71°10'W	838	S (SU)	87	0.4	T	–	7.13 (0.42)	76.46 (12.14)	–	7
Bernal 5 (9)	41°08'S; 71°10'W	844	S (SU)	33	0.3	T	–	7.3 (0.4)	62.18 (5.37)	–	7
Bernal 6 (9)	41°08'S; 71° 10'W	837	S (SU)	15	0.4	T	–	7.18 (1.09)	84.6 (10.14)	–	7
Ñirihuau 1 (10)	41°05'S; 71°10'W	771	S (SU)	1000	0.7	T	*	7.54 (0.47)	77.61 (9.94)	1	4, 7
Ñirihuau 2 (10)	41°05'S; 71°10'W	771	S (SU)	6.837	0.6	T	*	7.31 (0.42)	76.75 (18.52)	1	4, 7
Ñirihuau 3 (10)	41°05'S; 71°10'W	771	S (SU)	15.1	0.6	T	*	7.48^♦	68.96 (8.8)	1	7
Ñirihuau 4 (10)	41° 05'S; 71° 10'W	777	S (SU)	651.5	0.5	T	*	7.03 (0.49)	94.99 (7.32)	1	7
Capital letters indicate different landscape units: APF, Andean–Patagonian forest; SAF, Sub-Antarctic forest; S, steppe and transitional zone; U, urban; SU, suburban; R, remote; P, permanent water body; T, temporary or semi-temporary water body. Asterisks (*) indicate the presence of aquatic vegetation. Numbers indicate the presence of backswimmer and amphibian species: 1, Notonecta vereetbrugghenni; 2, N. virescens; 3, N. fazi; 4, Pleurodema thaul; 5, Hylorina sylvatica; 6, Batrachyla taeniata; 7, Pleurodema bufoninum; 8, Rhinella spinulosa; 9, Atelognathus nitoi. Diamonds (♦) indicate point values. NA, not available.

Figure 2  Plot of Axis 1 and 2 of the Canonical Correspondence Analysis applied to study the effects of environmental variables on the distribution of notonectid species in 21 ponds inside the Nahuel Huapi National Park (Patagonia, Argentina). Environmental variables are indicated by arrows. Numbers and black triangles refer to ponds: 1, Llao-Llao; 2, Fantasma; 3, Virgen de las Nieves; 4, Pinar de Festa; 5, Teleférico; 6, Mallín Ñireco; Ñireco 1 and 2; 7, Los Patos and Verde; 8, Refugio de Jesús; 9, Bernal 1 to 6; 10, Ñirihuau 1 to 4. Grey triangles indicate notonectid species.

Table 2  Results of the Canonical Correspondence Analysis (CCA) performed to study the distribution of notonectids in ponds belonging to Nahuel Huapi National Park.

Variables	Axis (r)	Axis 2 (r)	Lambda	Conditional effects testing
Altitude	0.988	−0.007	0.97	F=25.89, P=0.004
Depth	0.580	0.109	0.34	F=0.54, P=0.48
Area	−0.064	−0.450	0.08	F=2.13, P=0.146
pH	0.182	−0.024	0.03	F=0.28, P=0.6
Conductivity	−0.339	0.089	0.12	F=0.63, P=0.47
Vegetation	−0.680	0.071	0.46	F=1.6, P=0.232
Correlation coefficients (r) of the different variables with Axis 1 and 2. Eigenvalues (Lambda) of the environmental variables to Axis 1 and conditional effects testing are provided.

Figure 3  Seasonal abundance of Notonecta vereertbruggheni in Fantasma pond during 2008. The bars indicate density (mean±1SEM; ind/m³) of N. vereertbruggheni. Maximum body length of the different instars of Notonecta: I = 2 mm, II = 3.9 mm, III = 5.4 mm, IV = 8.9 mm, V = 9.8 mm, adult = 14 mm.

Figure 4  Ingestion rate (IR) (mean±1SEM; prey/pred./h) of different developmental stages of Notonecta vereertbruggheni on: a, the calanoid copepod Parabroteas sarsi and b, newly hatched tadpoles of Pleurodema thaul. IRs were calculated from laboratory feeding experiments in light and dark treatments.

Figure 5  Selectivity index (α) of Notonecta vereertbruggheni on Parabroteas sarsi calculated from mixed prey experiments exposing P. sarsi and newly hatched tadpoles of Pleurodema thaul, in light and dark treatments (mean±1SEM). The dashed line indicates maximum α (α=1). Values close to 1 indicate total preference for P. sarsi.