Bufo Calamita Research Articles

Effects of predator interactions, prey palatability and habitat structure on survival of natterjack toad Bufo calamita larvae in replicated semi-natural ponds

The significance of predation and aquatic habitat structures to the survivorship of natterjack toad Bufo calamita larvae was investigated by manipulating predator numbers and pond characteristics in a series of replicated semi-natural pools over three consecutive years Two species of fish (common carp Cyprinus carpio and perch Perca fluviatilis) increased the survival of small tadpoles severalfold by selectively consuming predatory invertebrates, but a third species of fish (rudd Scardinius erythrophthalmus) devoured tadpoles and invertebrates indiscriminately Survival of larger tadpoles later in larval development was less affected by the reduction of invertebrate predation pressure from carp and perch, probably because abiotic factors (pond desiccation and anoxia) were stronger agents of tadpole mortality In ponds of low pH (ca 4 5) there was greatly increased spawn mortality and reduced tadpole growth rates but no significant change in tadpole predation compared with circumneutral controls Neutralisation of acid ponds to pH 7 by addition of Ca(OH)2 restored spawn viability and tadpole growth rates to control levels without affecting predation level Addition of organic nutrients stimulated tadpole growth rates significantly m ohgotrophic ponds but not sufficiently to improve survival of small larvae in the face of predation Extensive growths of macrophytes increased predator numbers up to more than twofold but effects on tadpole mortality rates differed between experiments Replacement of natural substrates by concrete basins substantially increased tadpole survival throughout development, probably because both predation by invertebrates and abiotic mortality factors were ameliorated Predation was a strong force early in natterjack tadpole development irrespective of chemical and biological conditions within ponds, but became much less important compared with abiotic factors as an agent of mortality at later tunes

Reproductive ecology of Bombina variegata: characterisation of spawning ponds

Abstract The use of spawning sites by Bombina variegata was analysed in a dynamic habitat containing a variety of different ponds. Cool or shadowy as well as permanent ponds were not used for spawning at all. Among the ephemeral ponds that were used, egg numbers increased with water temperature, both when compared among ponds and between different areas within ponds. Egg numbers were also higher in ponds of intermediate duration than in those persisting for shorter or longer periods. Ponds of intermediate duration with moderate predator densities and with larvae of competing anuran species (Hyla arborea, Bufo calamita) were used more often than short-lived ponds with no predators and competitors. This pattern of spawn deposition can be interpreted as an attempt to select sites allowing rapid larval development (warm water) and to avoid sites with high numbers of newts and invertebrate predators (permanent ponds). The selection critera seem to be adaptive, because pond duration and desiccation are more important for larval survival than predators and competitors. Yet, optimal reproductive conditions remain highly unpredictable for Bombina variegata, as the characteristics and dynamics of spawning ponds are mainly determined by climatic conditions. Consequently, survival chances of tadpoles can change within a few days or weeks, depending on rainfall and evaporation.

Reaction norms for metamorphic traits in natterjack toads to larval density and pond duration

Reaction norms for metamorphic traits in natterjack toads to larval density and pond duration

Macroenvironmental factors as ultimate determinants of distribution of common toad and natterjack toad in the south of Spain

Macroenvironmental factors as ultimate determinants of distribution of common toad and natterjack toad in the south of Spain

Factors Affecting Population Densities of Adult Natterjack Toads Bufo calamita in Britain

The population densities of adult natterjack toads (Bufo calamita, Laurenti) were found to vary over an order of magnitude between different localities for this species in Britain. Adult toad population density correlated positively with average toadlet production over the previous decade at each site. Average toadlet production in turn correlated with breeding pond density at natterjack sites and the adult toad population size at one study site increased subsequent to an artificial increase of pond density. Toadlet production within particular ponds was positively correlated with spawn deposition rate and there was no evidence of density-dependent regulation of toadlet production in two natterjack breeding ponds studied over several years. The proportion of breeding seasons in which greater than the median number of toadlets was produced per hectare of total natterjack habitat was positively correlated with pond density at natterjack sites. Taken together, these data suggest that adult natterjack population density is primarily regulated by the average rate of metamorphic success at a site, and this in turn is dependent upon stochastic rather than density-dependent processes operating at the level of the breeding ponds.

Contributions of Quaternary palaeoecology to nature conservation

Abstract. Quaternary palaeoecology has traditionally been associated with the reconstruction of past biota and past environments over long time periods such as the Holocene period. Recent methodological developments and conceptual advances have resulted in an ‘applied palaeoecology’ that can address specific ecological and environmental questions over the last 100‐200 yr, the time span of primary interest to nature conservationists. The contributions of palaeoecology to the assessment of naturalness of ecosystems, to the assessment of the fragility of ecosystems, to the assessment of the conservation status of rare species, and to the development of a factual basis for attempts at ecosystem enhancement and restoration are discussed, with reference to palaeoecological studies in Scotland, England, southwest Ireland, and Sweden. Palaeoecological results indicate that few, if any, vegetation types in western Europe are natural. Palaeoecology can provide unique insights into the fragility of ecosystems in response to human activity and other biotic factors such as grazing and to acidification. Palaeoecology can contribute basic information required for understanding the causes of recent decline of taxa such as the natterjack toad, aquatic macrophytes, and arcticalpine plants. Palaeoecology is often the only source of baseline data about past ecosystem composition and function that are essential for any realistic attempts at ecosystem restoration or enhancement.

Macroenvironmental factors as ultimate determinants of distribution of common toad and natterjack toad in the south of Spain

We have analysed the relations between the distribution areas of Bufo bufo and Bufo calamita in the south of the Iberian Peninsula. In order to characterise the localities where the species were found, we used 24 environmental variables, and we tested their influence on the distribution of both species by nonparametric methods. By means of logistic regression we calculated the odds of finding one or other species in a locality. The environmental parameters that increase the probability of presence of each species and of both species together are related with the climatic stability and with the climatic subregions. Bufo bufo is more likely to be found in areas where the climate is more predictable, probably because in these areas it may exert its competitive superiority over B. calamita. In zones with very low climatic stability B. calamita is more likely to be found than B. bufo, probably because B. bufo lacks the ability to adapt to unpredictable conditions. In areas with intermediate climatic predictability B. bufo is present, but it would be prevented from removing B. calamita, and so the odds of finding each species are equilibrated. In these areas there would be a balance between the superior competitiveness of B. bufo and the higher adaptability of B. calamita. With the same logistic equation we characterise the typical habitats of each species, and also the environments shared by both species.

Double-clutching by natterjack toads Bufo calamita at a site in Southern England

Abstract The breeding behaviour of female natterjack toads Bufo calamita at an isolated population in Hampshire, UK was investigated over a period of four years. In all four breeding seasons some (2-10) females laid two clutches of spawn, the first direct evidence of double-spawning by natterjacks in the wild. The mean period between clutch depositions was 63 days and the first clutches contained about twice as many eggs as the second ones. Double-clutching females were significantly larger than single-clutching ones, but not significantly larger than early spawners which were found in amplexus again late in the season but which did not spawn a second time. Late spawn, including second clutches, failed to produce toadlets in any of the four years of study.

2nd World Congress of Herpetology

Abstract Natterjack toads (Bufo calamita) form metapopulations consisting of interacting local and temporal breeding assemblages. The gene flow between simultaneously reproductive local populations is limited at the adult stage to about 2% roaming males and around 20% of females. The gene flow between temporal populations breeding successively at the same locality is based on about 0–15% of males and 0–29% of females reproducing in different temporal breeding assemblages. The annual mortality rate of males ranges between 50 and 60%, corresponding to a maximum life expectancy of about 7 years. The main cause of local extinction is always deterioration of the habitat, namely destruction of the breeding habitat or a dry climate.

Negative Correlation between Length of Larval Period and Metamorphic Size in Natural Populations of Natterjack Toads (Bufo calamita)

Negative Correlation between Length of Larval Period and Metamorphic Size in Natural Populations of Natterjack Toads (Bufo calamita)

Plasticity in Metamorphic Traits of Natterjack Tadpoles: The Interactive Effects of Density and Pond Duration

Plasticity in developmental time and size at metamorphosis were studied in natural and experimental populations of natterjack toad tadpoles (Bufo calamita), a species which breeds in temporary ponds of variable duration. Amount of rainfall directly affected pond hydroperiod and larval density through an increase in the number of spawning females. As both factors directly affected larval period and thus metamorphic success, we performed a factorial field experiment to examine the response of developmental rates to drought regime and its interaction with population density, by controlling pond duration, larval density and food level. Timing of metamorphosis was affected by larval density and food level. However, the response among larvae due to pond duration was not additive. At low larval density, tadpoles raised in short duration ponds exhibited shorter larval periods than in long duration ponds. In constrast, plasticity in developmental rates due to pond duration was less marked at high larval densities and no difference in length of larval period was found. This may be the result of higher competition levels in short duration ponds through an increase in actual larval density because of decreasing water level and lower metamorphic rates. This higher competitive stress was also evident by smaller metamorphic size in short ponds. At low densities tadpoles in longer duration ponds exhibited no additional growth, indicating that tadpoles that remained for a longer period did not achieve larger metamorphic size. This outcome does not support an adaptive explanation of developmental plasticity that merely may be the consequence of expressing a single program of development in different habitats.

Ontogeny of Ocular Serotonin N-Acetyltransferase Activity Daily Rhythm in Four Anuran Species

The profile of daily ocular serotonin N-acetyltransferase (NAT) rhythm has been examined during the development of four anuran amphibians in different environments and of varying phylogenetic origins: Xenopus laevis, Discoglossus pictus, Rana perezi, and Bufo calamita. A significant day/night rhythm of ocular NAT with the acrophase at midnight was first detected at stages 43/44 and 25 in X. laevis and R. perezi, respectively. Total enzymatic activity increased with body weight throughout development, although both mean levels and amplitudes of NAT activity per milligram of protein significantly decreased; this attenuation of rhythm was more significant in postmetamorphic froglets, and the acrophase was delayed about 1 hr. There were no significant differences in daily NAT profiles before and after metamorphosis in D. pictus and B. calamita. The amplitude of the NAT rhythm was maximal (>10-fold nocturnal values) in Xenopus compared with other species (2- to 3-fold).

The basis of niche separation during terrestrial life between two species of toad (Bufo bufo and Bufo calamita): competition or specialisation?

Two congeneric anurans with highly overlapping geographical ranges, Bufo bufo and B. calamita, were investigated with respect to isolating mechanisms during the terrestrial phase of life in the three habitat types in which both species occur in Britain. Marked spatial niche separations were observed in all three habitats (coastal dunes, upper saltmarshes and lowland heaths). B. bufo was associated with complex, dense vegetation structures and had a relatively wide niche, while B. calamita had a narrower niche and occurred mostly on open, poorly-vegetated ground. Food niche overlap was high at all three study sites. Animals translocated into atypical habitats returned to their preferred type whenever possible, and suffered increased mortality or loss of condition if prevented from doing so. B. calamita operated at significantly higher body temperatures (by an average of 1.4° C) than B. bufo when hunting at night. Experiments in outdoor vivaria indicated that B. calamita survived in open habitats because individuals escaped desiccation in daytime by burrowing into the substrate, whereas B. bufo lacked this behaviour and perished on the inhospitable surface. By contrast, B. calamita individuals lost mass and became hyperactive in densely-vegetated conditions because their hunting efficiency was selectively reduced relative to that of B. bufo. Taken together, the data indicated that spatial niche separation between these species during the terrestrial phase of life was dictated primarily by behavioural and physiological factors, and not by competition.

Conservation of the natterjack toad Bufo calamita in Britain over the period 1970–1990 in relation to site protection and other factors

The number of known sites (populations) documented by conservationists for the natterjack toad Bufo calamita between 1970 and 1990 in Britain rose from 21 to 40, excluding those resulting from translocations. The progressive reduction in rate of discovery of undocumented sites suggests that few further populations will be located. The real overall number of natterjack sites has probably changed little over this period, with successful translocations approximately compensating for the few (three to five) concurrent extinctions. More than 90% of matterjacks in Britain now live in the vicinity of just five river estuaries. Habitat protection, mainly the result of scheduling land as Sites of Special Scientific Interest (SSSI), has been increasingly effective in safeguarding natterjacks, the proportion of safeguarded sites rising from 60% in 1970 to 83% by 1990. However, the legislation for species protection has proved much less effective. Much of the recent damage on unscheduled sites was a result of agricultural improvements by landowners ignorant of the presence of natterjacks on their land. The breeding records from natterjack sites are used to examine the possible impacts of radioactivity and climate change, against which site protection alone is no safeguard. Recommendations are made for conserving natterjack populations in the future.

Trying to save the natterjack toad — a case study in amphibian conservation: T. Beebee, British Wildlife, 3(3), 1992, pp 137–145

Trying to save the natterjack toad — a case study in amphibian conservation: T. Beebee, British Wildlife, 3(3), 1992, pp 137–145

Reproductive strategies in a female-biased population of natterjack toads, Bufo calamita

Abstract. The behaviour of male and female natterjack toads in an isolated population of about 100 adults in Hampshire, U.K. was investigated over a period of 5 years. Virtually all animals were individually identifiable (by toe-clipping and throat-spot patterns) during the study. Most males remained sexually active throughout the breeding season (April-June) but a significant minority (40-44%) of individuals, indistinguishable by size or survivorship from the population average, visited the ponds only for the first 2 weeks of the breeding seasons. The former group was more successful than the latter in amplexing with females. There was no general correlation between male body size and breeding success. Two distinct and about equally common spatial strategies were evident among breeding males: residents visited just one pond and called from it throughout the breeding season, while switchers moved irregularly between several ponds. These strategies were highly conserved by individuals between years, and were not related to body size. Switchers were more successful in obtaining females, and did not suffer higher mortality rates than residents. There was a direct correlation between the amount of male calling activity at a pond and its attractiveness to females. In any one year only 44-64% of females spawned. After the breeding season, females spent more time hunting than males during summer and autumn nights.

The Effect of Food Level on Competition in Tadpoles: Interference Mediated by Protothecan Algae?

1. The development of natterjack toad (Bufo calamita Laurenti) tadpoles was monitored under two levels of food and with or without competitors (Rana temporaria L.) using a replicated pond system. The design prevented physical interactions between species but allowed B. calamita access to R. temporaria faeces. 2. Food supplements accelerated growth with or without competitors. The presence of competitors depressed B. calamita growth, even under conditions of high food. 3. B. calamita raised under high food metamorphosed earlier than those raised under low food, but neither food nor competitors affected survival. 4. The growth-inhibiting alga, Prototheca, was detected in the faeces of both R. temporaria and B. calamita. B. calamita raised with R. temporaria for several weeks produced larger numbers of protothecan cells in their faeces than those raised without competitors. 5. Inferior competitors may be diverted from high quality food resources by the attractive properties of Prototheca in faeces. In such a situation superior competitors may exert a negative effect even under high food levels.

Do Male Natterjack Toads Join Larger Breeding Choruses to Increase Mating Success?

Male and female natterjack toads, Bufo calamita, exhibited a high degree of breeding synchronization. A polynomial or exponential regression indicated that the operational sex ratio (OSR) between nights increased with number of males in the overall population; hence, OSR varied temporally with chorus size. The comparison of three different groups of calling males within the breeding area, separated from each other and differing in male numbers, revealed similar OSRs between groups. Therefore, OSR did not vary spatially with chorus size. On average, males that attended larger groups obtained higher mating success in one season but not in another. Male movements between groups were directed toward larger groups, with higher OSRs and higher number of calling males, but males did not increase their mating probabilities by moving to another group. Female distribution among groups was correlated with the availability of oviposition sites, but they were not attracted differentially to large male groups or to groups with more callers.

Long-term management of a natterjack toad (Bufo calamita) population in southern Britain

Abstract We have investigated the dynamics of an isolated population of natterjack toads (Bufo calamita) over the period 1972-1991. During this time the habitat was manipulated by clearance of scrub woodland and by creation and restoration of ponds. The adult toad population increased at least threefold during the study, with a nadir in the late 1970s and a maximum in the late 1980s. Female population size, as judged by spawn string counts, varied according to metamorphic success rates three years previously. Ponds suitable for natterjack breeding on chemical and topographical grounds nevertheless varied both in their attractiveness to natterjacks and in their success rates in sustaining larvae through to metamorphosis; those desiccating at intermediate times were more successful than highly ephemeral or longer-lasting water bodies. Artificial eutrophication of one naturally acid pond by addition of Ca((OH)2 increased its attractiveness to natterjacks for several years but did not sustain high levels of toadlet production. Female natterjacks survived up to twice as long as the oldest males, a difference possibly attributable to selective predation by the snake Natrix natrix. Invertebrates, especially beetles (Coleoptera) and ants (Hymenoptera) were the primary food of both natterjacks and sympatric common toads (B. bufo) at the study site. Addition of fish (Leuciscus idus) to breeding pools reduced numbers of predatory invertebrates and increased toadlet production in two separate experiments. Optimal terrestrial habitat for natterjacks was sustained only for 2-3 years after scrub clearance, after which seral succession rendered it unsuitable.

Density‐related features of natterjack toad (Bufo calamita) population in Britain

We have studied a series of natterjack populations with varying densities of adults on the three main habitat types (lowland heaths, coastal dunes and coastal marshes) occupied by this species in Britain. Animals were aged by skeletochronology, condition was assessed by measuring weight length ratios in autumn and home ranges were determined by individual‐marking and by radiotelemetry. Female longevity was inversely correlated with population density, but no similar effect was observed for males. Uniformity of growth rates, absolute growth rates and mean condition for both sexes were also inversely related to population density, whereas mean home range showed a positive correlation. Taken together the data indicated that in high‐density populations natterjack toads grew more slowly and erratically, were in poorer condition and foraged much more widely than their counterparts in low‐density populations.