Study species
P. crispus (curly-leaf pondweed) is native to Eurasia and invasive in North and South America and New Zealand. It is a cold-adapted macrophyte with an optimum growth temperature in the range of 10–20°C (Ren et al., 1997; Tobiessen & Snow, 1984). Turions of the plant germinate in fall, overwinter with little growth, and subsequently grow fast during early spring after which their growth subsides and they eventually die and senesce in summer (Catling & Dobson, 1985; Tobiessen & Snow, 1984; Peiyu Zhang, Zhang, et al., 2021).V. spinulosa is endemic to China, mostly occurring in the middle and lower reaches of the Yangtze River (B. Wang et al., 2010), where it often coexists with P. crispus . V. spinulosa is a warm-adapted species with an optimum temperature for germination at approximately 20 °C (Wang et al., 2021).P. crispus turions and seedlings of V. spinulosa were obtained from another nearby lake, Lake Honghu (29°51′N, 113°20′ E).
The herbivore used in this experiment is Radix swinhoei (big-ear radix), a pulmonated freshwater snail widely distributed throughout Asia, and found in a diverse set of habitats, including lakes, ponds, streams, rivers, and rice fields (Ziu et al., 1979). R. swinhoei is a generalist grazer which feeds on both periphyton and macrophytes (K. Y. Li, Liu, Hu, et al., 2009; Xiong et al., 2010). R. swinhoeisnails were collected in a pond in Huazhong Agricultural University Fisheries College Base in Wuhan City, Central China (30°29′N; 114°22′ E).