Tommy Lennartsson

INDUCTION OF OVERCOMPENSATION IN THE FIELD GENTIAN, GENTIANELLA CAMPESTRIS

We present field evidence for the induction of overcompensation, or increased fruit and seed yield as a consequence of damage, in the grassland biennial field gentian, Gentianella campestris (Gentianaceae). We compared equally sized clipped and unclipped plants in two populations in central Sweden during three years, 1992-1994, and plants clipped at different occasions, from 20 June to 2 August. Clipping once, by removing half of the biomass, significantly increased fruit production without affecting the number of seeds per fruit or seed mass. The degree of compensation was sensitive to the timing of clipping. Damage induced overcompensation only during a restricted inductive time period (ITP) in July. Plants clipped before about 1 July or after about 22 July achieved no overcompensation. The early limit of ITP was presumably determined by the availability of resources that could be mobilized for regrowth after damage. The late limit, on the other hand, depended primarily on the differentiation of meristems close to flowering in early August. The effects of clipping varied between years, presumably due to drought in 1994. During 1992-1993, plants consistently overcompensated for clipping on 1-20 July, whereas in 1994 only early clipping from 1 to 12 July induced overcompensation. In 1994, plants clipped in late July compensated less well, due to delayed fruit maturation leading to a high proportion of immature fruits at the end of the season. Because of this between-year variation, we used geometric mean fitness to calculate the expected long-term effects of damage over generations. The analysis suggests that the long-term effects can vary from positive to negative, depending on the frequency of bad fruiting years. The time limits of ITP fit well the hypothesis that predictable damage in July may have selected for a capacity of overcompensation in the field gentian. Because the ultimate limits of ITP are set by the length of the vegetation period, we expect overcompensation in this species to be more common in regions with a longer growing season.

EVIDENCE FOR AN EVOLUTIONARY HISTORY OF OVERCOMPENSATION IN THE GRASSLAND BIENNIAL GENTIANELLA CAMPESTRIS (GENTIANACEAE)

Swedish University of Agricultural Sciences, Department of Conservation Biology, Section of Conservation Botany, Box 7072, 750 07 Uppsala, Sweden; University of Oulu, Department of Biology, Linnanmaa, 90 570 Oulu, Finland, and University of Lund, Department for Theoretical Ecology, Ecology Building, 223 62 Lund, Sweden; University of Lund, Department for Theoretical Ecology, Ecology Building, 223 62 Lund, Sweden

Tolerance of Gentianella campestris in relation to damage intensity: an interplay between apical dominance and herbivory

Meristem allocation models suggest that the patterns of compensatory regrowth responses following grazing vary, depending on (i) the number of latent meristems that escape from being damaged, and (ii) the activation sensitivity of the meristems in relation to the degree of damage. We examined the shape of compensatory responses in two late-flowering populations (59°20′N and 65°45′N) of the field gentian. Plants of equal initial sizes were randomly assigned to four treatment groups with 0, 10, 50 and 75% removal of the main stalk. The plants were clipped before flowering, and their performance was studied at the end of the growing season. The northern population showed a linear decrease in shoot biomass and fecundity with increasing biomass removal, while the response in the southern population was quadratic with maximum performance at the damage level of 50% clipping. This nonlinear shape depended upon the activation sensitivity of dormant meristems in relation to their position along the main stem. The highest plant performance was achieved by inflicting intermediate damage which induced regrowth from basally located meristems. In contrast, the topmost branches took over the dominance role of the main stem after minor apical damage (10% clipping). Consequently, the breakage of apical dominance is a necessary precondition of vigorous regrowth in this species. However, compensation in the field gentian is unlikely to be a mere incidental by-product of apical dominance. The ability to regrow from basally located meristems that escape from being damaged by grazing may well be a sign of adaptation to moderate levels of shoot damage.

The evolution of tolerance to damage in Gentianella campestris: natural selection and the quantitative genetics of tolerance

In the framework of phenotypic plasticity, tolerance to browsing can be operationally defined as a norm of reaction comparing plant performance in undamaged and damaged conditions. Genetic variation in tolerance is then indicated by heterogeneity in the slopes of norms of reaction from a population. We investigated field gentian (Gentianella campestris) tolerance to damage in the framework of phenotypic plasticity using a sample of maternal lines from natural populations grown under common garden conditions and randomly split into either a control or an artificial clipping treatment. We found a diversity of tolerance norms of reaction at both the population and family level: the impacts of clipping ranged from poor tolerance (negative slope) to overcompensation (positive slope). We detected heterogeneity in tolerance norms of reaction in four populations. Similarly, we found a variety of plastic architectural responses to clipping and genetic variation in these responses in several populations. Overall, we found that the most tolerant populations were late flowering and also exhibit the greatest plastic increases in node (meristem) production in response to damage. We studied damage-imposed natural selection on plasticity in plant architecture in 10 of the sampled populations. In general, there was strong positive direct selection on final number of nodes for both control and clipped plants. However, the total selection on nodes (direct + indirect selection) within each treatment category depended heavily on the frequency of damage and cross-treatment genetic correlations in node production. In some cases, strong correlated responses to selection across the damage treatment led to total selection against nodes in the more rare environment. This could ultimately lead to the evolution of maladaptive phenotypes in one or both of the treatment categories. These results suggest that tolerance and a variety of architectural responses to damage may evolve by both direct and indirect responses to natural selection. While the present study demonstrates the potential importance of cross-treatment genetic correlations in directing the evolution of tolerance traits, such as branch or node production, we did not find any strong evidence of genetic trade-offs in candidate tolerance traits between undamaged and damaged conditions.

Seasonal differentiation — a conservative reproductive barrier in two grasslandGentianella (Gentianaceae) species

Abstract18 populations of the grassland biennialsGentianella amarella andG. campestris were cultivated to clarify the genetical vs. environmental components of the flowering phenology, and the reproductive isolation caused by seasonal differentiation. The influence of some environmental factors was tested. The seasonal variation persisted in cultivation, and the plants could normally be assigned to distinct aestival or autumnal groups, with no reproductive contact. Flowering phenology was affected by environmental factors, but not to such an extent that the reproductive isolation was broken. The observed phenological variation was not reflected by a corresponding variation in present management practices. Management history and possible non-anthropogenic factors are discussed as alternative explanations.

Plant Adaptations to Herbivory: Mutualistic versus Antagonistic Coevolution

The discovery of overcompensatory responses to damage in some plant species has inspired attempts to classify some plant-herbivore interactions as mutualism. Since the debates over plant-herbivore mutualism and overcompensation have been intense, we attempt to outline three conceptual models of plant-animal interactions and evaluate the status of interactions with help of three different fitness criteria: relative fitness, absolute fitness, and mean absolute fitness. Our three plant-animal interactions are assumed to represent plant-pollinator mutualism, plant-herbivore antagonism and the evolution of overcompensation, respectively. Each case describes how absolute fitness, and consequently also the other two fitness criteria, is assumed to change with animal encounters for plants with special adaptations to cope with those encounters and for plants with no such adaptations. As a result, all these types of interactions may be considered as mutualism when taken relative fitness only into account. Obviously, this criterion is too weak because any trait, evolving under natural selection, should improve fitness relative to other, alternative traits. Absolute fitness increases with animal encounters for the adapted phenotype in the first and in the last case and thus, in the context of absolute fitness, overcompensation in plants would indicate plant-herbivore mutualism. However, absolute fitness as such may not be sufficient when discussing the evolutionary history of plant-animal mutualism. In the light of mean fitness, overcompensation as presented in earlier studies does not represent mutualism between plants and herbivores. Mean absolute fitness in plant populations decrease with the risk of herbivore attack in our model of overcompensation, while the reverse trend characterises our plant-pollinator model. We, therefore, suggest that mean absolute fitness may well provide an appropriate criterion for distinguishing mutualistic and antagonistic plant-animal interactions in coevolutionary contexts. In order to evaluate our model-system, we compare the predicted patterns with empirical data on the grassland biennial Gentianella campestris.

Managing biodiversity rich hay meadows in the EU: a comparison of Swedish and Romanian grasslands

Semi-natural hay meadows are among the most biodiversity-rich terrestrial ecosystems, and are managed for conservation purposes in most of Europe, including Sweden. Romania has some of Europes largest areas of grasslands still managed with traditional methods. Through interviews and field studies, current management practices were investigated in two Romanian villages, and compared with CAP-generated grassland management in Swedish hay meadows and historical Swedish management of grasslands. The study evaluated the effect of the eligibility criteria within both countries’ National Rural Development Programmes (NRDPs) on different ecologically important components of hay meadow management. The success of Swedish management was measured by assessing population trends for 25 grassland plant species. Current management proved to be considerably more diverse in Romania than in Sweden, but historical Swedish management was similar to management in Romania. Both countries’ NRDPs provide support for some management components, but create barriers against other components. The Romanian NRDP contained more barriers than the Swedish NRDP, yet Swedish management showed little success in preserving grassland plants. NRDPs should nourish the use of local and traditional knowledge in order to preserve biodiversity in semi-natural grasslands. There are major limitations in both countries’ NRDPs.

Biodiversity and Traditional Land Use in South-Central Sweden: The Significance of Management Timing

During the last 50–100 years, large numbers of species associated with seminatural grassland have declined. One reason for this is the considerable reduction of grassland area. Another possible explanation is the loss of historical management practices. This study addresses changes in the timing of management and its implications for biodiversity, and combines historical data on management timing (eighteenth century) with data on reproductive phenology of vascular plants and butterflies. All data are from south-east and south-central Sweden and demonstrate a considerable loss of grassland area, but an even greater loss of historical management practices. Historically, 21–32 per cent of the seminatural grassland area was subject to late season management (from early July A. DAHLSTROM, T. LENNARTSSON, J. WISSMAN AND I. FRYCKLUND 386 BIODIVERSITY AND TRADITIONAL LAND USE 387 Environment and History 14.1 Environment and History 14.1 onwards) by mowing or late-season grazing. In 2005, management had ceased in 97–99 per cent of the historically managed grassland, and current management was dominated by all-season grazing. 0.2 per cent of the grassland area was managed by mowing in 2005. Historically, at the time of mowing, 50–80 per cent of the butterfly species and 20–95 per cent of vascular plant species had completed their reproductive cycles, the proportions increasing with the later onset of management. The results suggest that the reduced use of late management is a major cause of the observed decline of grassland organisms.

Ecological significance and heritability of floral reproductive traits in Gentianella campestris (Gentianaceae)

Summary We investigated the occurrence of herkogamy and dichogamy in 43 populations of the grassland biennial Gentianella campestris in Sweden, and experimentally tested their significance for the reproductive system of the species. Furthermore, we performed a heritability test to evaluate the potential for selection on traits related to herkogamy. Dichogamy did not occur in the studied populations, and herkogamy was restricted to five populations. Two types of herkogamy were found, one with the stigma protruding above the anthers (hyper-stigmatic), and one with the stigma positioned below the anthers (hypo-stigmatic). In both types, the stamens elongated during anthesis. In the hyper-stigmatic plants, the anthers reached and pollinated the stigma after c. 34 days. This did not occur in hypo-stigmatic plants. Pollination experiments showed that the plants were self-compatible and that elongation of stamens provided a mechanism for reproductive assurance in hyper-stigmatic plants. The type of herkogamy did not differ between flowers of the same developmental stage within a plant. In two of the five herkogamous populations, the herkogamy differed between plants, but there was a normal distribution of the anther-stigma separation. Herkogamy was not related to population size. A comparison of the anther-stigma separation of self-pollinated mother plants and their offspring showed that herkogamy was a highly heritable trait (average h 2 = 0.85), that clearly has the potential to respond to selection

Effects of Timing of Grazing on Arthropod Communities in Semi-Natural Grasslands

Abstract Arthropod communities were investigated in two Swedish semi-natural grasslands, each subject to two types of grazing regime: conventional grazing from May to September (continuous grazing) and traditional late management from mid-July (late grazing). Pitfall traps were used to investigate abundance of carabids, spiders, and ants over the grazing season. Ant abundance was also measured by mapping nest density during three successive years. Small spiders, carabids and ants (Myrmica spp.) were more abundant in continuous grazing than in late grazing while larger spiders, carabids, and ants (Formica spp.) were more abundant in late grazing. The overall abundance of carabids was higher in continuous grazing in the early summer but higher in late grazing in the late summer. The switch of preference from continuous to late grazing coincided with the time for larvae hibernating species replacing adult hibernating. We discuss possible explanations for the observed responses in terms of effects of grazing season on a number of habitat variables for example temperature, food resources, structure of vegetation, litter layer, competition, and disturbance.