Biological properties of the endemic and threatened shrub in Iberia Vella pseudocytisus subsp. paui Gómez Campo (Cruciferae) and implications for its conservation

We present new data about chorology, seed bank, dispersal, seedling biology and population structure of the threatened endemic shrub Vella pseudocytisus subsp. paui Gómez Campo in Spain. In addition, we investigate human activities that are linked with the fine-scale distribution of the taxon to offer conservation recommendations.Currently, the plant occurs in two populations close to the city of Teruel (East central Spain), growing in an open shrubby community on patches of gypsum substrate surrounded by agricultural landscape. The plant has disappeared from two reported locations dated from early 20th Century likely due to human activities.The seed bank seems to be poor. A ballistic dispersal mechanism appears to move seeds between 0 and 4 m. We did not find a clear seasonal pattern of seedlings emergence although spring cohorts are the largest. Also, this period was where leaf seedling growth was more prominent. During the 3 years of our survey, the cumulative mortality was 94.2% of all seedlings plants. Plants are estimated to remain in the seedling stage for approximately 5 years. The demographic structure of both populations shows no apparent gaps in the distribution of size classes. Adult plants greater than 200 dm³ represent the most important stage for seed production and persistence.We point out two key factors for conservation purposes, first the weakness of some of the plant biological properties for natural establishment and second its ability to colonise artificial environments. We propose a mitigation of clonal spread in those sites and the protection of juvenile stages in more natural locations.     

Variability in nectar production and standing crop, and their relation to pollinator visits in a Mediterranean shrub

Nectar standing crops in flowers within an individual plant are often highly variable. This variability may be a by-product of the foraging activity of insect pollinators. Alternatively, plants may be selected to produce highly variable rewards to reduce consecutive visitation by risk-averse pollinators, thus diminishing within-plant pollen transfer. This study evaluated the roles of pollinator control vs. plant control over nectar variability in the bee-pollinated shrub Rosmarinus officinalis L. (Lamiaceae). We sampled nectar production, standing crop and pollinator visits in three shrubs of one population over 17 days during one blooming season. Nectar production rates were highly variable (CV = 1.48), and increased after rainy days. Nectar standing crops were even more variable (CV = 2.16), decreased with increasing temperatures, and increased with time since the last rain. Pollinator visit rates decreased with variability in nectar standing crops, increased with flower number per shrub, and were unaffected by variability in nectar production rates. Repeated sampling of marked flowers revealed no correlation between their nectar standing crops and production rates. These findings support the role of reward variance in reducing pollinator visits, but suggest that plants are not in complete control of this variability. Rather, plant-generated variability can be modified by intensive foraging activity of pollinators. Such pollinator control over nectar variability is likely to reduce the selective advantage of plant-generated reward variation. Handling Editor: Neal Williams.     

Demographic variation in cycad populations inhabiting contrasting forest fragments

Reduced habitat quality after fragmentation can significantly affect population viability, but the effects of differing quality of the remaining habitat on population fitness are rarely evaluated. Here, I compared fragmented populations of the cycad Zamia melanorrhachis from habitats with different history and subject to contrasting levels of disturbance to explore potential demographic differences in populations across habitat patches that could differ in habitat quality. Secondary-forest fragments had a lower canopy cover and soil moisture than remnant-forest fragments, which may represent a harsh environment for this cycad. A smaller average plant size and lower population density in the secondary-forest fragments support the hypothesis that these fragments may be of lower quality, e.g., if plants have reduced survival and/or fecundity in these habitats. However, variation in the stage-structure of populations (i.e., the relative proportions of non-reproductive and reproductive plants) was associated with the area of the forest fragments rather than the type of habitat (remnant versus secondary forest). These results suggest that different demographic parameters may respond differently to habitat fragmentation, which may be explained if processes like adult survival and recruitment depend on different characteristics of the habitat, e.g., average light/water availability versus suitable area for plant establishment. This study shows that forest fragments may differ drastically in environmental conditions and can sustain populations that can vary in their demography. Understanding how forest fragments may represent different habitat types is relevant for evaluating population viability in a heterogeneous landscape and for designing conservation programs that account for this heterogeneity.     

The reproductive biology and effective pollinators of the endangered beardtonguePenstemon penlandii (Scrophulariaceae)

Penland's beardtongue, a rare endemic plant of the Colorado Plateau, displays a mixed breeding system. Plants are partially self-compatible but set more fruits when cross-pollinated than when self-pollinated. Fruit production is significantly increased by pollinators. However, in two years of study there was no indication that fruit set was being limited by inadequate pollinator visitation. Pollinator effectiveness was judged by correlating bee behavior at the flowers with analysis of the pollen carried on bee bodies. The most important pollinators were native megachilid bees, particularly in the genusOsmia. The bees that pollinate Penland's beardtongue are essential to its reproduction and must be preserved along with this rare plant.     

Demographic traits of Eotetranychus pruni from Belgian and Tunisian orchards,in comparison with Tetranychus urticae

Eotetranychus pruni was recorded in Belgian and Tunisian apple orchards for the first time. The aim of this study was to compare a Belgian (Vieusart) and a Tunisian strain (Grombalia), with respect to their life history and demographic traits. Furthermore, a Tunisian strain of Tetranychus urticae (Sousse) was also added to the study, in order to evaluate the potential status of the Tunisian strain of E.pruni. Experiments were carried out in the laboratory(24 °C) on apple leaf discs. Significant differences were noticed between the two species, with respect to development time (males),fecundity and fertility (egg hatching), but no differences could be detected between the two strains of E. pruni. Life tables were setup to describe the population statistics. The calculated intrinsic rates of natural increase (r _m) appear to be rather lowper se and do not correspond to those of typical “rstrategic pests”. The Bootstrap procedure allows us to estimate the confidence interval for these r _m values. By using this method, the two Tunisian strains (T. urticae and E. pruni) appear to be quite similar, and contrast with the Belgian strain (E. pruni). The potential pest status of the Tunisian strain of E. pruni is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Multivariate analysis of the response of overgrown semi-natural calcareous grasslands to restorative shrub cutting

Monitoring and evaluation of restoration management often suffers from poor sampling design and a lack of statistical rigour, seldom considering the spatial and temporal variability of habitat. We tested the effectiveness of shrub cutting on the restoration of calcareous grasslands, using a 4-year Before–After/Reference-Control-Impact (BARCI) project design with replicated patches of habitat. Departure from the control sites and convergence with the reference sites were analysed using the Principal Response Curves (PRC) method.The structure of communities was compared 1 year before and 3 years after management on control scrubland, restored ex-arable land, restored and reference grassland. Results show that shrub cutting did not suffice to restore the community composition of the semi-natural calcareous grasslands. The restored ex-arable areas maintained a community structure extremely similar to the control scrubland.The restored grassland, on the other hand, deviated from the control and slightly converged to the reference grassland, though not significantly. The dominant scrub species that was cut, Prunus spinosa, showed higher cover values compared to the reference grassland in any of the treatments, even the first year after cutting. Species typical of xeric and/or calcareous grassland were more abundant in the reference than in the restored grassland, while arable and ruderal species were more frequent in the restored sites.This study has demonstrated that the BARCI approach is a powerful tool for the evaluation of restoration management, as it was possible to evaluate not only departure from the unmanaged control, but also convergence with the reference community. The PRC method provided a comprehensive overview of the response of the 153 species involved in the study.Our results also indicate that the second PRC should be considered, when significant, to not exclude important information from the assessment.     

Purifying Selection and Demographic Expansion Affect Sequence Diversity of the Ligand-Binding Domain of a Glutamate-Gated Chloride Channel Gene of Haemonchus placei

Ninety-five genomic sequences of the ligand-binding domain of glutamate-gated chloride channel genes of three populations of the parasitic nematode H. placei were evaluated for patterns of diversity, demography, and selection. These genes code for subunits of ion channels, which are involved in the mode of action of the most commonly used antiparasitic drugs, the macrocyclic lactones. An extremely high frequency of unique segregating sites in exons and introns was observed, with significantly negative neutrality tests in each population for noncoding, synonymous, and nonsynonymous sites. Several tests indicated that support for balancing selection, positive selection, and hitchhiking was lacking. McDonald–Kreitman tests using H. contortus or C. elegans as an outgroup revealed an extreme excess of replacement polymorphism, consistent with weak purifying selection. Although these tests agree that negative selection may explain the excess of replacement changes, an alternative interpretation is required for the significantly negative Fu and Lis D statistics based on silent and noncoding sites. These include homogeneous forces such as background selection and demographic expansion. The lack of population subdivision and the negative values of Tajimas D for this outbreeding parasitic nematode render background selection less likely than demographic expansion. Comparison of D statistics based on different site types using neutral coalescent simulations supported this interpretation. Although this statistic was more negative for nonsynonymous sites than for synonymous sites, most comparisons of the D statistic were not significantly different between mutation classes. A few significant site comparisons were also consistent with demographic expansion, because the observed test statistic (D_neutral – D_selected) were low relative to the neutral expectations. Finally, previous mitochondrial studies also identified a demographic expansion of this parasitic nematode species, which lends further support to a scenario involving both demographic and purifying forces in the ligand-binding domain of H. placei.     

Combined effects of heat shock, smoke and darkness on germination of Epacris stuartii Stapf., an endangered fire-prone Australian shrub

Epacris stuartii (Epacridaceae) is an endangered heathland shrub in which seedling recruitment occurs almost exclusively after fire. Seed viability and multiple seed dormancy mechanisms were examined to explore why levels of seedling recruitment were low after some fires, despite high rates of pre-fire seed production. The individual and combined effects of heat shock, smoke derivatives and darkness on germination were tested in the laboratory using an orthogonal logit-linear model, a form of analysis ideally suited to hypotheses concerning multiple germination cues. Seed viability (56%) was found not to be limiting. After 89 days of incubation, germination was significantly enhanced by heat shock, smoke treatment and continuous darkness but there were no significant interactions. These effects were equal in magnitude and additive such that maximum germination (42% of viable seeds) was stimulated when all three treatments were combined, significantly less germination occurred in response to any two treatments combined (22–23%), any single treatment stimulated germination at levels (10–11%) significantly less than two treatments and the lowest levels of germination occurred among untreated seeds (4%). Relative to the untreated control, germination was stimulated by smoke derivatives in high concentrations but not in low concentrations. The effect of darkness diminished with time so that after 270 days of incubation darkness had no significant effect on germination, while heat and smoke still enhanced germination significantly, additively and interchangeably. More prolonged germination of seeds exposed to light on the soil surface than buried seed may spread the risk of desiccation of emerging seedlings over multiple rainfall events. The role of heat and smoke derivates suggests that fire management is a crucial tool for influencing seedling recruitment and hence the survival of E. stuartii at its only known location. Received: 3 November 1996 / Accepted: 15 June 1997     

Genetic diversity and phenotypic variation in marginal populations of the locally endangered speciesHordeum secalinum (Poaceae)

Electrophoresis was used to compare variation in hordein polypeptide patterns and isozymes in five marginal populations ofHordeum secalinum (four Swedish and one Danish population) and four populations along the Atlantic coast from Denmark to Spain. Hordein patterns were uniform within and among Swedish and Danish populations whereas the materials from France and Spain were divergent. The banding patterns for nine isozymes (AAT, IDH, MDH, PGD, GPI, ME, ACP, EST, and PRX) agreed with those reported for otherHordeum species. All putative loci were monomorphic with the exception of PRX, which showed three different phenotypes. The five marginal populations varied in seed set and cultivated plants differed in phenological traits.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

Deferred agonistic behavior in a long-lived scincid lizard Eumeces laticeps

Summary A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred.Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.     

Hierarchical pre-dispersal fitness assessment in a Mediterranean shrub plant

Under the concept of modularity, it is possible to recognise how seed production, as well as any other process affecting it, are hierarchically structured within fruits, within individual plants and within populations. In this work, we analysed the effects of pre-dispersal seed predation by insects upon a set of hierarchical levels in a population of the Mediterranean shrub plant Cistus ladanifer (“rock rose”) throughout a complete fruit-producing season (which takes place during the summer months). Almost all individual plants were predated, which implies that the effects of predation at the population level (regardless of the extent of predation within each individual) were virtually uniform. Within the individuals, however, the predation rate was close to a proportion of 0.5 (half of the fruits of each individual were predated), which indicates that this hierarchical level is likely to be subjected to a differential action of selection. Predation rates within the fruits showed an intermediate value (lower than that observed at the population level but higher than that at the individual level). According to these results, the pressure of phenotypic selection may therefore give rise to greater variation among fruits of the same individual than among seeds of the same fruit. In terms of the temporal patterns observed there was a large variation in the increments of predation along the fruiting season, which implies a high degree of heterogeneity in the temporal distribution of the effects of predation pressure on fitness. Besides its use in the specific example of the plant species studied in this work, the methodological procedure presented in this paper (integration of the temporal changes of different hierarchical levels) might be foreseen, in fact, as a useful tool for analysing the hierarchical structuring of fitness in modular organisms in general. This procedure allows to discriminate and integrate selection pressures and their effects across different phenotypic levels, from the infra-individual ones up to the population level.     

Adaptive introductions: How multiple experiments and comparisons to wild populations provide insights into requirements for long-term introduction success of an endangered shrub

Recovery of an imperiled plant species may require augmentation of existing populations or creation of new ones. Hundreds of such projects have been conducted over the last few decades, but there is a bias in the literature favoring successes over failures. In this paper, we evaluate a series of introductions that experimentally manipulated microhabitat and fire in an adaptive introduction framework. Between 2002 and 2012, we (and our collaborators) carried out ten introductions and augmentations of Florida ziziphus Pseudoziziphus (Condalia, Ziziphus) celata, a clonal shrub limited to very small populations and narrowly endemic to pyrogenic central Florida sandhills. Six of the introductions were designed as experiments to test hypotheses about how demographic performance was affected by microhabitat, fire, and propagule type. Introduced transplants had high survival (<90% annually), inconsistent growth, and little transition to reproduction, while introduced seeds had low germination and survival. Transplants were more efficient than seeds as translocation propagules. Shaded (vs. open) sites supported generally higher transplant and seedling survival and seed germination percentages, but growth responses varied among experiments. Supplemental irrigation increased transplant survival and seed germination, but otherwise seedling and plant survival and growth were not significantly affected. Contrary to expectations based on wild populations, introduced propagules have not been more successful in unshaded sites, suggesting that Florida ziziphus has broader microhabitat preferences than hypothesized. Compared to wild plants, introduced plants had similar survival and responses to fire, slower growth, and more delayed flowering. Introduced plants had no clonal spread. While no introduced population has demonstrated a capacity for long-term viability, one augmented population has flowered and produced viable fruits. Given that Florida ziziphus genets are long-lived, low levels of sexual reproduction may be adequate for the establishment of viable populations. Thus, after many translocations over more than a decade, it is premature to characterize any single translocation as a success or a failure, underscoring the need for a long view of translocation success.     

毛乌素沙地三种灌木群落的水分利用过程

沙地柏、黑沙蒿和沙柳是毛乌素沙地的3种优势灌木群落。利用稳定同位素技术研究了3种灌木及伴生植物杨柴主要利用的水分来源,结合叶片稳定碳同位素值与土壤水分监测,从而确定灌木群落如何利用水分。结果表明:7月和9月3种群落内浅层土壤水的稳定氧同位素值接近雨水。沙地柏5月主要利用25 cm浅层土壤水,而7月和9月主要利用10—25 cm浅层和100—200 cm深层土壤水。黑沙蒿和伴生的杨柴5月主要利用10 cm浅层土壤水,7月同时利用10 cm浅层土壤水和150 cm深层土壤水,9月则利用10—150 cm土壤水。沙柳5月主要利用10—25 cm浅层土壤水,伴生的杨柴主要利用50—200 cm土壤水;7月它们同时利用10—25 cm浅层土壤水和100—200 cm深层土壤水;9月都主要利用25—200 cm土壤水。4种植物的叶片稳定碳同位素值存在季节动态和种间差异。常绿灌木沙地柏的叶片碳同位素值比较稳定,而且高于其他3种落叶灌木和半灌木。5月浅层土壤含水量较低时3种落叶植物的叶片碳同位素值较高。因此,降雨补充的浅层土壤水是3种灌木群落利用的主要水分来源。3种灌木及其伴生植物根据不同深度土壤水的...     

Influence of temporal heterogeneity in nitrogen supply on competitive interactions in a desert shrub community

Soil nutrients in arid systems are supplied to plants in brief pulses following precipitation inputs. While these resource dynamics have been well documented, little is known about how this temporal heterogeneity influences competitive interactions. We examined the impacts of the temporal pattern of N supply on competitive intensity and ability in an N-limited desert shrub community. At our field site, the three codominant shrubs, Atriplex confertifolia, A. parryi, and Sarcobatus vermiculatus, differ in seasonal growth patterns, with A. confertifolia and S. vermiculatus achieving higher growth rates earlier in the growing season than A. parryi. We predicted that these timing differences in maximum growth rate may interact with temporal variation in N supply to alter competitive abilities over time. Seedlings of the two Atriplex species were planted either individually in field plots or as target plants surrounded by neighbor seedlings. After one year of establishment, the same amount of ¹⁵N was applied to plots either as early spring pulses, mid spring pulses or continuously through the second growing season. Competitive effects were observed under continuous and pulsed N supply. Averaged across all target–neighbor treatments, competitive intensity was ∼1.8-fold greater when N was pulsed compared to when N was supplied continuously, but overall, the outcome of competitive interactions was not influenced by N pulse timing. While the timing of resource supply did not differentially influence the competitive abilities of coexisting species in this system, the temporal pattern of resource supply did alter the intensity of competitive interactions among species. While additional studies in other systems are needed to evaluate the generality of these results, this study suggests that competitive intensity may not necessarily be a direct function of productivity or resource availability as traditionally assumed. Instead, the intensity of competitive interactions in resource-poor systems may depend upon the temporal pattern of resource supply.     

Adaptive on-line simulation of bioreactors: Fermentation monitoring and modeling system

Summary In order to study and control fermentation processes, indirect on-line measurements and mathematical models can be used. Here an on-line model for fermentation processes is presented. The model is based on atom and partial mass balances as well as on stability equations for the protolytes. The model is given an adaptive form by including transport equations for mass transfer and expressions for the fermentation kinetics. The state of the process can be estimated on-line using the balance component of the model completed with measurement equations for the input and the output flows of the process. Adaptivity is realized by means of on-line estimation of the parameters in the transport and kinetic expressions using recursive regression analysis. On-line estimation of the kinetic and mass transfer parameters makes model-based predictions possible and enables intelligent process control while facilitating testing of the validity of the measurement variables. A practical MS-Windows 3.1 model implementation called FMMS—Fermentation Monitoring and Modeling System is shown. The system makes it easy to configure the operating conditions for a run. It uses Windows dialogs for all set-ups, model configuration parameters, elemental compositions, on-line measurement devices and signal conditioning. Advanced on-line data analysis makes it possible to plot variables against each other for easy comparison. FMMS keeps track of over 100 variables per run. These variables are either measured or estimated by the model. Assay results can also be entered and plotted during fermentation. Thus the model can be verified almost instantly. Historical fermentation runs can be re-analyzed in simulation mode. This makes it possible to examine different signal conditining filters as well as the sensitivity of the model. Combined, the data analysis and the simulation mode make it easy to test and develop model theories and new ideas.     

Demographic costs of Chaoborus-induced defences in Daphnia pulex: a sensitivity analysis

Summary We examined the demographic costs of Chaoborus-induced defensive spine structures in Daphnia pulex. Our aim was to assess the role of resource limitation and the interaction effects of limiting food level and antipredator structures on fitness of D. pulex and to pinpoint those life stages that are most sensitive to changes in the defence regime. Chaoborus-induced and typical morphotypes of D. pulex were reared at high and low food concentrations. Instar-based matrix population models were used to quantify the effects of predator-induction, food and their interaction on fitness of D. pulex. Predator-induction caused a statistically significant reduction in fitness at low food levels, but not at high food levels. Sensitivity analyses revealed that the fitness effects were primarily due to changes in the growth rate in instars 1–5, and secondarily to small reductions in the fertility of instars 5–10. The interaction between Chaoborus exposure and low food concentration was negative, and mediated through growth and fertility components. Both these components were reduced more in the Chaoborus-exposed, low food treatment than would be expected in the absence of interaction.     

Conservation of moths in The Netherlands: population trends, distribution patterns and monitoring techniques of day-flying moths

The loss of butterfly diversity in north-western Europe has been studied extensively but much less is known about the status of other macrolepidoptera. The present paper presents results of the research on mainly day-flying larger moths carried out by Dutch Butterfly Conservation in The Netherlands. Research started in 1992 with a public campaign and a mapping programme, leading to an increase in the number of records of macrolepidoptera. Results from the mapping programme on day-flying moths showed a strong general decrease in The Netherlands, comparable with the loss of butterfly diversity. Transect counts have been undertaken since 2000 for a few species and this method is sufficient to measure trends over time if the moth densities are high enough. Another research component was to focus on marshland habitats in The Netherlands. Fifty-five characteristic marshland moth species were selected and the relative abundance of nearly all these species has declined. These trends were compared with four other countries in the Atlantic biogeographical zone. The relative abundance of the majority of marshland moths in The Netherlands was found to be higher than those in other European countries, so that The Netherlands has a special responsibility for the conservation of the moths of its marshes. Moreover, we emphasise that, next to butterflies, moths can be of great use in nature conservation because of their potential significance as indicator species in endangered habitats.     

The consequences of specialization for pollination in a rare South African shrub,Ixianthes retzioides (Scrophulariaceae)

Ixianthes retzioides is a rare South African shrub with large yellow oil-secreting flowers. Populations studied previously revealed low levels of reproductive success and the absence of a specialized oil-collecting pollinator. We report the discovery of a population in which the predicted specialist pollinator,Rediviva gigas, is present. The presence of this oil-collecting bee resulted in a mean fruit set per plant of 97.2 ± 8.3% (N = 9) and a mean seed set of 331.6 ± 162.6 (N = 52). This represents a 7.4-fold increase in fruit set and a 7.8-fold increase in seed set over a previously studied population lacking the specialist pollinator. The contrast between populations with and without the specialist pollinator dramatically illustrates the potential benefits and costs of specialization for pollination, respectively.     

Biochemical markers in a species endangered by introgression: The red wolf

The red wolf (Canis rufus), native to much of the southeastern United States, is endangered by man's activities and by hybridization with other species of the genus Canis. The absence of diagnostic morphological markers to distinguish the red wolf from its hybrids has led to the application of the methods of biochemical genetics to this problem. The finding of a unique electrophoretically determined allele with a distribution congruent with the geographical distribution of the remaining red wolf population is reported.This research was supported by NIH Public Health Service Grants GM 19513 and CA 19311 and by the State of Texas.     

Demographic costs of Chaoborus-induced phenotypic plasticity in Daphnia pulex

Summary It has been proposed that morphological defenses against predation have demographic costs. We measured the cost of a predator-induced morphological defense, using predaceous phantom midge larvae Chaoborus americanus (Insecta, Diptera) and the prey species Daphnia pulex (Crustacea, Cladocera). The induced defense is a neck tooth (and other pleiotropic structures) developed in juvenile D. pulex in the presence of C. americanus. Laboratory life table experiments, in the absence of predation, indicated the population growth rate of typical D. pulex was 11% to 39% greater than that of D. pulex exposed to C. americanus extract, or C. americanus-conditioned water. The reduction in population growth rate was most frequently associated with an increase in the time between birth and first reproduction. Induced individuals required twenty more hours at 23°C, and twenty five more hours at 20°C, to develop to the age of first reproduction. Under limiting food conditions age-specific survivorship and the number of offspring produced per female by the induced form were reduced relative to the typical form. As a result, the difference in population growth rates among forms was greater at the low food level as indicated by a highly significant food by form interaction effect. In addition to neck teeth and lowered reproductive rates, the offspring of induced form individuals had significantly longer tail-spines (7.2–7.5%), and primiparous adults from the induction treatment were significantly shorter than controls (3–8%).