Small prey size offers immunity to predation: a case study on two species of Asplanchna and three brachionid prey (Rotifera)

Abstract

We tested the hypothesis that small prey can coexist with large predators. For this we confronted two predators (smaller Asplanchna brightwellii: 900 mm and larger A. sieboldi: 1400 mm) with three prey rotifers (smaller: Anuraeopsis fissa (70 mm); larger: Brachionus calyciflorus (200 mm) and intermediate: B. patulus (120 mm)) using functional response, prey preference, population growth and life table demography. Regardless of prey type, A. sieboldi was able to consume more prey than A. brightwellii and it consumed higher number of B. patulus than of B. calyciflorus or A. fissa. Prey preference experiments showed that A. brightwellii had no preference for B. calyciflorus regardless of prey density, while A. sieboldi preferred B. calyciflorus and avoided A. fissa. Data on population growth showed that A. brightwellii was always numerically more abundant than A. sieboldi. Prey type had a significant effect on peak abundances of A. sieboldi but not of A. brightwellii. Life table demography data revealed a significantly lower lifespan in A. brightwellii fed B. calyciflorus, compared to B. patulus, but not when compared to A. fissa. A. sieboldi lifespan was not affected by prey type. Depending on prey type and predator species, generation time varied from 2 to 3 days. Both lowest (0.38 d À1 ) and highest (0.98 d À1 ) population growth rates were observed in A. sieboldi. We suggest that reduced reproductive output in Asplanchna was caused by either large (B. calyciflorus) or small (A. fissa) prey. At natural densities of Anuraeopsis, it is unlikely that Asplanchna reaches abundances high enough to exterminate this prey. By its extremely small size (combining low energetic profitability with low encounter rates with predators) A. fissa may coexist with Asplanchna in nature.

Contrasting Zooplankton Assemblages in Two Oxbow Lakes with Low Transparencies and Narrow Emergent Macrophyte Belts (Krapina River, Croatia)

“…We presumed, at times of higher transparency, that the increased risk of fish predation also caused copepods to shift to the littoral zone, generating significant differences in their spatial distribution which is in compliance with results of MIRACLE et al (2007). Furthermore, we explained that the peak of abundance of the predator A. priodonta in the first part of spring by a positive correlation with its prey, K. cochlearis (SARMA and NANDINI, 2007). We can conclude that microfilter-feeders show more differences along a spatial scale (mainly feed on detritus), while macrofilter-feeders follow seasonal patterns in their abundance as they are dependent on phytoplankton production.…”

Predatory rotifer Asplanchna brightwellii mediated competition outcome between Brachionus calyciflorus and Brachionus patulus (Rotifera)

“…These findings are consistent with previous works associated with competition between rotifers of different size under various food levels (Sarma et al, 1996(Sarma et al, , 1999. However, compared to B. calyciflorus, B. patulus is more vulnerable to predatory Asplanchna (Iyer & Rao, 1996;Nandini et al, 2003;Sarma & Nandini, 2007). Therefore, as shown in the present work, B. patulus, a superior competitor in non-predator environments, becomes an inferior competitor in the presence of a predator.…”

“…Previous studies showed that B. patulus was competitively superior to B. calyciflorus (Sarma et al, 1999), however, it was also more vulnerable to predatory Asplanchna than B. calyciflorus (Iyer & Rao, 1996;Nandini et al, 2003;Sarma & Nandini, 2007). Therefore, we hypothesized that the superior competitive status of B. patulus would be altered in the presence of predatory Asplanchna, and moreover, this alteration could be influenced by different intensities of predation imposed by different densities of Asplanchna.…”

“…Brachionus) (Fernando et al, 1990;Sarma, 1993;Iyer & Rao, 1996). The vulnerability of prey rotifer species to the predatory Asplanchna is largely determined by body size, encounter rate and handle time (Hampton & Starkweather, 1998;Nandini et al, 2003;Sarma & Nandini, 2007). For those planktonic rotifers, small individuals are more vulnerable than large ones (Iyer & Rao, 1996;Nandini et al, 2003).…”

Predatory and toxic effects of the turbellarian (Stenostomum cf leucops) on the population dynamics of Euchlanis dilatata, Plationus patulus (Rotifera) and Moina macrocopa (Cladocera)

“…These include the presence of large and small spines in Plationus macracanthus and Brachionus budapestinensis, respectively (Garza-Mouriño et al, 2005), darting behaviour in Filinia longiseta and Hexarthra mira (Iyer & Rao, 1996), small body size in Anuraeopsis fissa (Sarma & Nandini, 2007), epizoic behaviour in Brachionus rubens (Iyer & Rao, 1995) and colonial life or production of toxins as in Sinantherina semibullata (Felix et al, 1995). Little information is available on the defense strategies of littoral rotifers.…”