Small monsters: Insect predation limits reproduction of yellow‐bellied toad Bombina variegata to ponds in their earliest successional stage

Abstract

1. The disappearance and deterioration of amphibian breeding habitats is a major cause of their global extinction. In Europe, this problem affects the yellow-bellied toad Bombina variegata, which inhabits small ponds in the early stages of succession, where no predatory invertebrate species normally occur. Nonetheless, as habitats, small temporary ponds are highly endangered, a situation that is intensifying with urban spread. 2. A system of 13 pairs of artificial ponds was constructed in 2012 for the breeding of B. variegata with the aim of reconnecting disjunct populations. During the 2 years of the study, one of the twin ponds was regularly cleared of emergent vegetation and invertebrates. The survival rates of the tadpoles released in the cleared and uncleared ponds were analysed.3. The survival rate of the tadpoles released into the cleared ponds was higher than of those introduced into the uncleared ones. Tadpole survival rates were also higher in new, single ponds, constructed in 2013.4. The lower survival rates of the introduced tadpoles are best explained by the presence of predatory aquatic invertebrates, particularly the large diving beetle Dytiscus marginalis. Experimentally obtained consumption rates indicate that oneDytiscus larva is capable of destroying a typical clutch of B. variegata tadpoles within a few hours, much faster than any of the other insect predators tested.5. The impact of freshwater invertebrates on tadpoles is frequently studied but rarely quantified. For conservation measures to be effective, quantitative standards need to be applied that describe the impact of predation in a predictable manner.6. Construction of artificial small ponds is broadly accepted as an important conservation measure compensating for the disappearance of natural amphibian breeding sites. This function of artificial ponds may be substantially enhanced by the periodic removal of invertebrate predators.

Compensatory recruitment allows amphibian population persistence in anthropogenic habitats

“…This striking and rather nonintuitive result indicates that changes in management practices may have contrasting effects on B. variegata demography. By reducing habitat alterations within protected areas, wildlife managers can reduce rates of mortality of adult toads, but this may have the undesirable effect of decreasing adult recruitment, most likely because predator densities in ponds increase predation on tadpoles (25,27). Our findings are congruent with previous studies showing that human disturbance plays an essential role in maintaining suitable artificial breeding waterbodies (49,50) and contributes to the persistence of B. variegata populations in quarries, farmland, and logged forests (8,25).…”

“…1). B. variegata breeds in small waterbodies that are affected by frequent disturbances; consequently, they remain at an earlysuccessional stage with low densities of aquatic predators, with the result that tadpole survival and adult recruitment in these anthropogenic habitats are increased (25)(26)(27). Natural habitats correspond to environments where the main disturbance sources that determine the presence and renewal of breeding waterbodies (i.e., rocky pools on riverbanks and puddles associated with intermittent streams and springs) are natural phenomena, such as floods, desiccation, and landslides (25,28).…”

“…Second, human disturbance that is detrimental to adult survival could increase reproductive success by modifying the conditions prevailing in waterbodies during larval growth. For instance, vehicle traffic on unpaved roads causes disturbance to temporary waterbodies that form in ruts, reducing submerged aquatic vegetation and the density of predatory insects (such as Odonate larvae), thereby increasing tadpole survival and reproductive success (27,49,50). Likewise, logging operations that destroy extant breeding sites may also create new ones where breeding probability and success are higher than before due to increased exposure to sunlight (36) and a relative scarcity of predatory aquatic insects (27).…”

Tastier than thought? Telemetric research reveals predation on the poisonous yellow‐bellied toad Bombina variegata

“…The study was conducted in the Biała River Valley (southern Poland) in 2012–2013 as part of a European Union (EU) project on restoring the connectivity of the ecological corridor in this valley (Łaciak et al, 2022). One of the project's objectives was to introduce yellow‐bellied toads into an area from which they had earlier disappeared.…”

Extreme rainfall flushes out tadpoles of the yellow‐bellied toad Bombinavariegata from its breeding ponds

“…One oft‐mentioned reason for these population declines relates to changes in land use, which have substantially reduced the availability of breeding habitats suitable for this toad throughout its distribution. It usually spawns in small ponds in early successional stages, where there are no predatory insects or fish (Barandun & Reyer, 1998; Hartel et al, 2007, 2011; Sinsch et al, 2020; Łaciak et al, 2022). In the Carpathians, it commonly spawns in anthropogenic habitats like pools and puddles on dirt roads in forests, particularly wheel ruts filled with rainwater (Babik & Rafiński, 2001; Csanády et al, 2020; Rafińska, 1991).…”