Terrestrial Stages Research Articles

Evolution of complex life cycles of amphibians: bridging the gap between metapopulation dynamics and life history evolution

Current evolutionary models for amphibian life cycles reflect tradeoffs in size-specific growth and mortality rates between the aquatic and terrestrial stages. A limitation of these models is that they do not incorporate evolutionary phenomena that are associated with metapopulation structure. In this work I address components of the evolution of complex life cycles (CLCs) that are tied to the metapopulation dynamics of amphibians that use seasonal wetlands that vary in hydroperiod. In particular, I describe how selection for the minimum length of the larval period affects metapopulation viability and the selection/migration equilibrium. Selection to increase the minimum length of the larval period functionally reduces the number of viable breeding sites on the landscape, increases the average distance between neighboring sites, and increases the risk of metapopulation extinction. Within a metapopulation, asymmetric gene flow between populations that are adapted to different hydroperiods tends to swamp local selection for long larval periods at sites with long hydroperiods. The evolutionary stability of CLCs of many species with metapopulation structure may reflect the fact that extremely small metamorphs cannot survive on land, while lineages with long larval periods incur a high risk of metapopulation extinction. I encourage theorists to more carefully consider how life history traits and metapopulation viability are related for these and other taxa.

Morph switching in a dimorphic population of Triturus alpestris (Amphibia, Caudata)

The usual life cycle of Alpine newts comprises an aquatic larval stage and a terrestrial juvenile and adult stage. However, some populations differ from this pattern in exhibiting facultative paedomorphosis where some individuals reach sexual maturity while retaining larval traits such as gills and gill slits. While paedomorphic newts can, in some circumstances, initiate metamorphosis, once a newt has commenced metamorphosis, the state is irreversible. Because the frequency of this switching from one morph to the other has never been quantified in the wild, we attempted to estimate switching rate and survival by carrying out a 3-year monitoring survey of a population inhabiting an alpine lake. While morph switching did occur in this population, it involved a relatively low proportion of the paedomorphs (approx. 12%), suggesting that metamorphosis is not favoured in the study population. The hypothesis of paedomorphic advantage was not supported since neither survival nor body condition differed between morphs. The ontogenetic pathway of wild Alpine newts is thus characterised by two forks in the developmental pathway. The first occurs during the larval stage (metamorphosis vs. paedomorphosis), and the second occurs in paedomorphic adults (switching for metamorphosis vs. continuation of the paedomorphic lifestyle). Such a two-level decision process may allow individuals to cope with environmental uncertainty.

Ecological characterization and cladocerans, calanoid copepods and large branchiopods of temporary ponds in a Mediterranean island (Sicily, southern Italy)

Temporary waters have been sporadically investigated in Sicily. These environments reflect the climatic features of the Mediterranean area with a winter ponding phase and a more or less prolonged dry period in summer. Their biota, especially those organisms strictly linked to aquatic environments and without any terrestrial life stage, have to exhibit special adaptations to survive the dry phases that are recurrent in such ecosystems. This study included more than 250 water bodies distributed on the whole Sicilian territory and on the small circum-Sicilian islands. This paper represents a first attempt to characterize Sicilian temporary waters from an ecological point of view and is mainly based on some of their limnological features and on the crustacean components of their communities. In particular, the groups which have been taken into consideration are those of cladocerans, calanoid copepods, and large branchiopods (notostracans, anostracans, and spinicaudatans).

An individual based model of a sea turtle population to analyze effects of age dependent mortality

Effective conservation of wildlife species relies on our ability to recognize interactions among critical life stages, leading to the design of the appropriate protection measures. We developed an individual based model to analyze the variability of extinction probabilities as a result of interacting mortalities at different life stages of a sea turtle population. We conducted several simulation with different combinations of mortality rates for both terrestrial stages (i.e. egg and hatchling), and also for all marine stages of the species. To test and assess the implication of the numerous simulation sets produced by the fluctuating survival rates, counter plots were employed. The results of the simulation analysis show that the pelagic stage has a significant effect on population persistence. It is also apparent that increased survival of the first year cohort could to some extent be beneficial for the population. The need for additional demographic data and a better understanding of the behavioral and biological processes is highlighted.

Carryover Aquatic Effects On Survival Of Metamorphic Frogs During Pond Emigration

In organisms with complex life cycles, physiological stressors during early life stages may have fitness-level impacts that are delayed into later stages or habitats. We tested the hypothesis that body size and date of metamorphosis, which are highly responsive to aquatic stressors, influence post-metamorphic survival and movement patterns in the terrestrial phase of an ephemeral pond-breeding frog by examining these traits in two populations of northern red-legged frogs (Rana aurora aurora). To increase variation of body size at metamorphosis, we manipulated food availability for 314 of 1045 uniquely marked tadpoles and estimated the probability that frogs survived and emigrated using concentric rings of drift fencing surrounding ponds and Bayesian capture-recapture modeling. The odds of surviving and emigrating from the ponds to the innermost drift fences, approximately 12 m, increased by factors of 2.20 (95% credibility intervals 1.39-4.23) and 2.54 (0.94-4.91) with each millimeter increase in snout-vent length and decreased by factors of 0.91 (0.85-0.96) and 0.89 (0.80-1.00) with each day's delay in metamorphosis for the two ponds. The odds of surviving and moving to the next ring of fencing, 12 m to approximately 40 m from the ponds, increased by a factor of 1.20 (0.45-4.06) with each millimeter increase in size. Our results demonstrated that body size and timing of metamorphosis relate strongly to the performance of newly metamorphosed frogs during their initial transition into terrestrial habitat. Carryover effects of aquatic stressors that reduce size and delay metamorphosis may have population-level impacts that are not expressed until terrestrial stages. Since changes in both aquatic and terrestrial systems are implicated in many amphibian declines, quantifying both immediate and delayed effects of stressors on demographic rates is critical to sound management.

Interaction between biotic and abiotic factors determines tadpole survival rate under natural conditions

:The estimation of survival rates and the assessment of factors influencing variation in survival are essential to understanding population dynamics. However, in amphibians that alternate between an aquatic larval stage and a dispersing terrestrial stage, such understanding is limited due to the difficulty of estimating survival under field conditions. In this study, we obtained precise estimates of daily survival rates of tadpoles under field conditions using capture-mark-recapture (CMR) methods and assessed their temporal and spatial variation. Specifically, we assessed the effect of temperature, intra-specific density, and the presence of introduced bullfrogs (Rana catesbeiana) on the survival rate of Pacific treefrog (Pseudacris regilla) tadpoles in southern Vancouver Island, British Columbia, Canada. Daily survival rates of tadpoles were relatively constant within a season and were also similar between years. Survival rates in different ponds varied from 95.4 to 87.9 %·d-1. Among-pond differences in survival were best explained by the interaction of temperature and tadpole density. At low tadpole densities, survival increased with temperature, but at high densities, survival decreased with increasing temperature. It was not possible to detect the effect of introduced bullfrogs over the variation accounted for by differences in temperature and intra-specific density. As in terrestrial vertebrates, biotic and abiotic factors interacted strongly to determine survival rates in these tadpoles.

LOCAL AND LANDSCAPE INFLUENCE ON AMPHIBIAN OCCURRENCE AND ABUNDANCE

The traditional emphasis in ecology on local species interactions has recently broadened to include landscape-level processes. I used data from a seven-year survey of ponds in northern Switzerland to judge the relative contributions of local and landscape influences to the occurrence and density of larvae of eight amphibian species. Each pond was sampled twice each year using pipe samples and dip nets. Analyses evaluated support for a series of alternative models, some suggested by current ideas in aquatic ecology and others designed to reveal the impact of key variables. Results strongly supported models that include both local and landscape covariates. Species differed in preference for permanent or temporary ponds, high- or low-predator ponds, and landscapes within forested or open areas. The occurrence of all species was positively correlated with the densities of other species, suggesting that competition was less important than variation in quality among sites. The results emphasize the importance of local processes in governing the status of populations, because even landscape-level effects were probably caused by availability of habitat during the terrestrial stage, rather than by metapopulation processes.

Tree hole odonates as environmental monitors: Non-invasive isolation of polymorphic microsatellites from the neotropical damselflyMegaloprepus caerulatus

Because of their complex mating behaviour and life cycle (alternating aquatic and terrestrial stages) odonates provide important model systems for environmental monitoring, evolutionary ecology, and conservation genetics. Many odonate species are endangered and call for the use of non-invasive molecular studies. In the neotropical damselfly Megaloprepus caerulatus we have identified polymorphic microsatellite loci by means of the randomly amplified microsatellite technique (RAMS; Ender et al. 1996). Using the DNA from each a single leg of three unrelated individuals we screened 63 RAPD primers for small size banding patterns. A total of 95 RAPD profiles was hybridized with digoxigenin labelled di- and trinucleotide repeats (GAn ,G T n ,C A n and AATn) and 36 RAPD fragments harbouring microsatellite motifs were isolated. Cloning and sequencing of positive fragments revealed five polymorphic microsatellite loci. Since Megaloprepus caerulatus is a viable bio-indicator for primary rainforests the microsatellite system can be used to study the effects of forest fragmenation on population viability.

PATTERNS OF NATURAL SELECTION ON SIZE AT METAMORPHOSIS IN WATER FROGS

Strategies for optimal metamorphosis are key adaptations in organisms with complex life cycles, and the components of the larval growth environment causing variation in this trait are well studied empirically and theoretically. However, when relating these findings to a broader evolutionary or ecological context, usually the following assumptions are made: (1) size at metamorphosis positively relates to future fitness, and (2) the larval growth environment affects fitness mainly through its effect on timing of and size at metamorphosis. These assumptions remain poorly tested, because data on postmetamorphic fitness components are still rare. We created variation in timing of and size at metamorphosis by manipulating larval competition, nonlethal presence of predators, pond drying, and onset of larval development, and measured the consequences for subsequent terrestrial survival and growth in 1564 individually marked water frogs (Rana lessonae and R. esculenta), raised in enclosures in their natural environment. Individuals metamorphosing at a large size had an increased chance of survival during the following terrestrial stage (mean linear selection gradient: 0.09), grew faster and were larger at maturity than individuals metamorphosing at smaller sizes. Late metamorphosing individuals had a lower survival rate (mean linear selection gradient: -0.03) and grew more slowly than early metamorphosing ones. We found these patterns to be consistent over the three years of the study and the two species, and the results did not depend on the nature of the larval growth manipulation. Furthermore, individuals did not compensate for a small size at metamorphosis by enhancing their postmetamorphic growth. Thus, we found simple relationships between larval growth and postmetamorphic fitness components, and support for this frequently made assumption. Our results suggest postmetamorphic selection for fast larval growth and provide a quantitative estimate for the water frog example.

Timing and duration of Last Interglacial conditions in Europe: a chronicle of a changing chronology

Estimates of the length of the Last Interglacial in Europe, conventionally defined by the presence of forest as inferred from pollen diagrams, have varied considerably. Here an account of recent developments, largely instigated by a paper by Kukla et al. (1997), is presented. These include the emergence of new records with improved chronologies and a re-evaluation of previous assumptions of synchroneity between marine and terrestrial stage boundaries and also between northern and southern European changes. The current scheme proposes that the onset of the Last Interglacial in Europe started well into MIS 5e, after deglaciation was complete and was coincident with a rise to peak sea-surface temperatures. However, the timing of the end of the Last Interglacial between northern and southern Europe appears to have diverged considerably: in the north the elimination of forest occurred ca 115 ka, near the time of the MIS 5e/5d transition, while in the south tree populations persisted into the interval of global ice growth, until the onset of significant ice rafting ca 110 ka. This significant N–S diachroneity may be a reflection of the effects of different bioclimatic parameters limiting tree growth in the two areas. These developments highlight the problems of correlating records of different proxies and from different geographical regions.

PATTERNS OF NATURAL SELECTION ON SIZE AT METAMORPHOSIS IN WATER FROGS

Strategies for optimal metamorphosis are key adaptations in organisms with complex life cycles, and the components of the larval growth environment causing variation in this trait are well studied empirically and theoretically. However, when relating these findings to a broader evolutionary or ecological context, usually the following assumptions are made: (1) size at metamorphosis positively relates to future fitness, and (2) the larval growth environment affects fitness mainly through its effect on timing of and size at metamorphosis. These assumptions remain poorly tested, because data on postmetamorphic fitness components are still rare. We created variation in timing of and size at metamorphosis by manipulating larval competition, nonlethal presence of predators, pond drying, and onset of larval development, and measured the consequences for subsequent terrestrial survival and growth in 1564 individually marked water frogs (Rana lessonae and R. esculenta), raised in enclosures in their natural environment. Individuals metamorphosing at a large size had an increased chance of survival during the following terrestrial stage (mean linear selection gradient: 0.09), grew faster and were larger at maturity than individuals metamorphosing at smaller sizes. Late metamorphosing individuals had a lower survival rate (mean linear selection gradient: −0.03) and grew more slowly than early metamorphosing ones. We found these patterns to be consistent over the three years of the study and the two species, and the results did not depend on the nature of the larval growth manipulation. Furthermore, individuals did not compensate for a small size at metamorphosis by enhancing their postmetamorphic growth. Thus, we found simple relationships between larval growth and postmetamorphic fitness components, and support for this frequently made assumption. Our results suggest postmetamorphic selection for fast larval growth and provide a quantitative estimate for the water frog example.

Habitat Use and Movements of Repatriated Wyoming Toads

We studied habitat use and movements of a repatriated population of federally endangered Wyoming toads (Bufo baxteri) after the breeding season at Mortenson Lake. Albany County, Wyoming, USA. We followed 8 adult toads using telemetry (n = 68 relocations) during periods of activity and observed 59 post-metamorphic juvenile toads (n = 59 locations). Adult toads used habitat with a greater mean vegetation canopy cover (mean = 52.6%) than juveniles (mean = 39.20%). We found adults farther from the shoreline (mean = 1.32 m) than juveniles (mean = 1.04 m). Substrates used by toads had a mean surface temperature of 20.31 °C for adults and 23.05 °C for juveniles. We found most adult and juvenile toads on saturated substrates. All adult toads sampled did not move outside of a 30 x 500 m area along the east-to-south shore where they were captured. Toads were active diurnally through the end of October. We found toads torpid at night. We compared our results to a similar study of the historic population and found that adult toads of the current population used denser vegetation than those of the historic population. Unlike many bufonids, terrestrial stages of the Wyoming toad appear to depend on saturated substrates. The best logistic regression predictors of adult and juvenile toad presence were surface temperature and distance to shore. Survey transects within the moist margin of the lake (≤10 m from water) and after substrates have reached temperatures ≥20 °C will likely yield more detections.

Clearcut logging restricts the movements of terrestrial Pacific giant salamanders (Dicamptodon tenebrosus Good)

Pacific giant salamanders (Dicamptodon tenebrosus Good) in the Chilliwack River valley of southwestern British Columbia are at the periphery of their range, and therefore of conservation concern. Although logging is a potential threat to the species, no studies have examined how clear-cutting affects its terrestrial stage. We used radio telemetry to compare the movements of 35 terrestrial Pacific giant salamanders at sites with three different logging histories: forested, clearcut to the stream margin, and clearcut with riparian buffer strips. The results demonstrate that logging affected movements of the salamanders. Salamanders in clearcuts remained significantly closer to the stream, spent more time in subterranean refuges, and had smaller home ranges than those at forested sites. During a dry year, salamanders in clearcuts were significantly more dependent on precipitation for their movement than salamanders in forested habitats. Salamander movement behavior in riparian buffer strips was not significantly different from that at forested sites but was significantly different from that at clearcut sites. Riparian buffer strips appear to mitigate some of the negative effects of clearcuts on salamander movement.

Larval anurans with synchronous and asynchronous development periods: contrasting responses to water reduction and predator presence

Summary The larvae of pond breeding frogs experience high rates of mortality, predominantly through predation and pond desiccation. We investigated how the tadpoles of two common species of frog respond to these hazards using factorial experiments conducted in a laboratory. The eastern brown froglet Crinia signifera Girard spawns in small, highly ephemeral ponds, while the spotted marsh frog Limnodynastes tasmaniensis Günther breeds in more permanent water bodies. Prior to our experiments it was known that C. signifera siblings develop quickly and reach metamorphosis comparatively synchronously ( c . 25–35 days), while L. tasmaniensis grow and develop more slowly and time to metamorphosis is highly asynchronous ( c . 60–300 days). It was anticipated that these species would have different strategies for coping with declining water and predators. A separate experiment was conducted for each species. The factors were Hydroperiod (either constant or gradually declining water volume) and Predator (either the presence or absence of a restrained mosquitofish Gambusia holbrookii Girard). A random block design was used with six replicates for each possible combination of the factors ( N = 24). Each replicate consisted of a 13‐l tub of water containing 20 tadpoles. Newly emerged frogs were transferred to one of 24 vivaria. In the arrangement of the vivaria, we maintained the block design of the experiment. Crinia signifera tadpoles responded to declining water by accelerating development and so reduced time to metamorphosis. However, the resulting metamorphs were smaller and survival rate in the terrestrial stage was significantly lower. This is a clear demonstration of the benefit and cost of phenotypic plasticity in metamorphic traits. Limnodynastes tasmaniensis tadpoles experiencing declining water were also smaller at metamorphosis, but there was no evidence that they had reduced the time to metamorphosis compared with those in constant water. Moreover the survival rates of the resulting frogs did not differ. Consequently no adaptive plasticity can be inferred. The data suggest that L. tasmaniensis has a bet‐hedging strategy in which some siblings develop more quickly at the expense of size, while others take much longer but are bigger at metamorphosis as a result. Tadpoles of both species showed clear behavioural responses to the presence of the predator. They tended to occupy the non‐predator halves of the tubs in replicates where a mosquitofish was present. Neither species altered development rate in the presence of the predator and there was no detectable impact on survivorship in the terrestrial stage.

Impacts of sediment loads, tadpole density, and food type on the growth and development of tadpoles of the spotted tree frog Litoria spenceri: an in-stream experiment

The impact of increased-deposited sediment loads on growth and development of tadpoles of the spotted tree frog, Litoria spenceri, in south-eastern Australia was assessed in conjunction with food type and tadpole density. This investigation was conducted in stream enclosures subjected to varying treatments of tadpole density, substrata and deposited-sediment load. Tadpole growth and development were not significantly affected by food type, but there was a trend toward increased performance on periphyton substrata. Tadpole growth and development were significantly reduced by increases in tadpole density and sediment load. These effects were independent, suggesting that increased sediment load reduced food quality rather than quantity. Activities in catchments that increase sediment loads in streams may adversely affect growth and development of tadpoles of L. spenceri. Increased sediment input into streams may therefore reduce tadpole fitness and recruitment to the terrestrial stage. Disturbance processes that increase stream sediment loads, such as forestry activities and associated road construction, may potentially have contributed to the observed declines of L. spenceri and other lotic anurans in south-eastern Australia.

Trait-mediated indirect effects and complex life-cycles in two European frogs

Most animals actively avoid predators. If such a reaction reduces competitive ability, for example by reducing food intake, predator presence can lead to trait-mediated indirect effects. Because predator avoidance typically leads to reduced growth rather than reduced survival, its effect on population processes is difficult to assess. This is especially true for organisms with complex life-cycles, where predator avoidance during one stage is expected to lead to traitmediated indirect effects if it has effects reaching into the following life stages. I experimentally investigated the effect of caged (thus non-lethal) dragonfly larvae on the competition between tadpoles of two frog species (Rana lessonae and R. esculenta) and on juvenile frog survival during the subsequent terrestrial stage. In response to caged predators, R. lessonae delayed metamorphosis more than R. esculenta, but they both metamorphosed heavier. These differences suggest the possibility of a competitive disadvantage for R. lessonae in the presence of predators, which could lead to trait-mediated indirect effects. However, the presence of predators did not modify competitive effects and had no measurable consequences on terrestrial survival. Regardless of the presence of predators, competition during the larval stage had large effects on metamorphosis and led to strongly decreased survival in the subsequent terrestrial stage. These results suggest that trait-mediated indirect effects are not important in this system, because the predator reaction of the tadpoles in both species had no measurable effect on the following life stage and, therefore, probably no strong effect on community dynamics.

Establishing a terrestrial chronological framework as a basis for biostratigraphical comparisons

The palynological signature of interglacial deposits in the fragmentary European terrestrial record has often been used as the basis for determining their chronostratigraphical position and ultimately their age. This has placed emphasis on the presence/absence and abundance of certain characteristic taxa, but given the lack of continuous stratigraphies and independent chronologies, it has been difficult to assess the extent to which this strategy has produced reliable schemes. Here, an alternative approach is adopted whereby a chronological framework is developed for long and continuous pollen sequences from southern Europe. This in turn allows the emergence of a complete stratigraphical scheme of major vegetation events for the last 430 thousand years (ka) and the evaluation of the stage record of different taxa and their potential diagnostic value for biostratigraphical correlation. The comparison shows distinct similarities among some temperate stages of the terrestrial equivalent complexes of Marine Isotope Stages (MIS) 5 and 7 and also of MIS 9 and 11, but examination of combined records of taxa provides a possibility to differentiate between individual stages. A numerically-derived dichotomous key for the terrestrial stages based on the palynological records of 10 taxa is presented. Carpinus, Fagus, Abies, Pterocarya and Buxus emerge as the best ‘indicator pollen types’ because of their variable behaviour from one stage to the next, possibly a result of their late expansion within a temperate stage or reduced genetic variability. The analysis shows that the palynological signature of a temperate deposit can constrain the range of chronostratigraphical possibilities, but vegetation and palynological variability arising from local factors could result in difficulties in making a definite assignment at individual sites.

Hybridization in leopard frogs (Rana pipiens complex): terrestrial performance of newly metamorphosed hybrid and parental genotypes in field enclosures

Terrestrial ecology has been largely neglected in the study of amphibian life histories because it is difficult to manipulate most species during the terrestrial stage. I examined the terrestrial performance of Rana blairi, Rana sphenocephala, and four hybrid (two F1 and two advanced generation) genotypes in replicated experimental enclosures to test for differences in traits related to juvenile terrestrial fitness. I produced all genotypes by means of artificial fertilizations using frogs collected from natural populations in central Missouri, and juvenile frogs were obtained from larvae reared in experimental ponds. Following metamorphosis, froglets were raised in single-genotype groups in terrestrial enclosures through the first overwintering. The proportion surviving did not vary among genotypes, but the power to detect significant differences was low. F1 hybrid genotypes BS and SB demonstrated significantly higher growth rates than either parental species or advanced-generation hybrid genotypes. Observation of growth rates of advanced-generation hybrids equal to those of the parental species, and heterosis in F1 hybrids for growth rate, suggests that natural hybridization between R. blairi and R. sphenocephala can produce novel and relatively fit hybrid genotypes. Direct measurement of multiple fitness components for hybrid and parental genotypes is critical for assessing the evolutionary potential of natural hybridization in organisms with complex life cycles.

Late- and Postglacial Sea-Level Change and Paleoenvironments in the Oder Estuary, Southern Baltic Sea

Knowledge of sea-level change in the southern Baltic Sea region is important for understanding the variations in late Pleistocene and Holocene sea-level change across northern Europe. These variations are a consequence of the response of the Earth's crust to the deglaciation of Fennoscandia and of the water added to the oceans from the melting of all Pleistocene ice sheets. The sedimentological and geochemical composition of five sediment cores from the lagoonal Oder Estuary offers new observational evidence for sea-level change and coastal development in the southern Baltic Sea region. The combined use of several geochemical proxies (organic carbon, nitrogen, calcium carbonate and biogenic opal contents, Corg/S and Corg/N ratios, δ13C values of organic matter, and δ15N values) is a new approach for the study area. The chemical evidence of this multiproxy approach allows clear identification of several stages in the development of the lagoonal environment: postglacial lake stages with sandy sedimentation during the Older Dryas and the Allerød stades, lacustrine phases with high autochthonous productivity during the Atlantic stade, terrestrial stages with peat formation at the beginning of the Subboreal stade, sedimentation as a result of marine transgression, and brackish sedimentation after the formation of sand spits and barrier islands during the Subatlantic stade. The stages are the result of regional sea-level change owing to complex shoreline development. They support the tentative sea-level curve proposed nearly 20 years ago for the region. In addition, changes in Oder River input in response to climate conditions is monitored. Whereas high terrigenous input of organic matter from the Oder River occurred during periods of humid climate during the Allerød, Atlantic, and Subatlantic stades, Oder River discharge decreased with drier and cooler climate conditions during the Subboreal stade. Furthermore, the geochemical evidence points to local anomalies such as the significance of river input and additional sulfate supply into the Oder lagoon for the composition of the sediments. Overall, the results provide a framework for future studies, which would allow for a more detailed comparison with other, similar environments.

Photosynthetic pathway diversity in a seasonal pool community

1. Photosynthetic pathway diversity was evaluated for the dominant species in a seasonally aquatic community in the south‐western USA using 14C pulse‐chase techniques. 2. Under submerged conditions, only about half of the species were clearly C3, three of the 15 dominants were CAM, one species was C4 and three were potentially assimilating carbon with both C3 and C4 fixation. 3. During the brief terrestrial stage in the life history of these amphibious plants, both the CAM and the C3 + C4 species switched to C3, whereas the C4 species did not switch. 4. Numerous variations were apparent; for example, the C4 species, while exhibiting a biochemical pathway indistinguishable from terrestrial C4 plants, lacked Kranz anatomy in the aquatic foliage. Also, despite well‐developed CAM in several species, others exhibited low‐level diel changes in acidity, apparently not indicative of CAM. 5. Species with C4 or CAM CO2 concentrating mechanisms lacked the capacity for bicarbonate uptake, an alternative CO2 concentrating mechanism found in certain C3 species in this community. 6. Rubisco/PEPC in aquatic foliage was higher in C3 species than in C4, CAM or putative C3 + C4 species. In the terrestrial phase, as expected, the switch from CAM or C3 + C4 to strictly C3 assimilation was associated with a substantial increase in Rubisco/PEPC. Quite unexpected, however, was the substantial increase in this ratio in terrestrial C3 foliage. It is hypothesized that submerged C3 plants utilize PEPC for recycling of respiratory CO2 and/or C4 phototrophism under field conditions of limited CO2 and O2 saturation, and this is lost in the terrestrial foliage.