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Time lags in responses of organisms to deteriorating environmental conditions delay population declines and extinctions. We examined how local processes at the population level contribute to extinction debt, and how cycles of habitat deterioration and recovery may delay extinction. We carried out a demographic analysis of the fate of the grassland perennial Primula veris after the cessation of grassland management, where we used either a unidirectional succession model for forest habitat or a rotation model with a period of forest growth followed by a clear-cut and a new successional cycle. The simulations indicated that P. veris populations may have an extinction time of decades to centuries after a detrimental management change. A survey of the current incidence and abundance of P. veris in sites with different histories of afforestation confirmed the simulation results of low extinction rates. P. veris had reduced incidence and abundance only at sites with at least 100 years of forest cover. Time to extinction in simulations was dependent on the duration of the periods with favourable and unfavourable conditions after management cessation, and the population sizes and growth rates in these periods. Our results thus suggest that the ability of a species to survive is a complex function of disturbance regimes, rates of successional change, and the demographic response to environmental changes. Detailed demographic studies over entire successional cycles are therefore essential to identify the environmental conditions that enable long-term persistence and to design management for species experiencing extinction debts.

In conservation management, there is an urgent need for estimates of population viability and for knowledge of the contributions of different life-history stages to population growth rates. Collection of long-term demographic data from a study population is time-consuming and may considerably delay the start of proper management actions. We examined the possibility of replacing a long-term temporal data set (demographic data from several years within a population) with a short-term spatial data set (demographic data from different populations for the same subset of two continuous years) for stochastic estimates of population viability. Using matrix population models for ten perennial plant species, we found that the matrix elements of spatial data sets often deviated from those of temporal data sets and that matrix elements generally varied more spatially than temporally. The appropriateness of replacing temporal data with spatial data depended on the subset of years and populations used to estimate stochastic population growth rates (log λs). Still, the precision of log λs estimates measured as variation in the yearly change of logarithmic population size rarely differed significantly between the spatial and temporal data sets. Since a spatiotemporal comparison of matrix elements and their variation cannot be used to assess whether spatial and temporal data sets are interchangeable, we recommend further research on the topic.

The joint effects of multiple herbivores on their shared host plant have received increasing interest recently. The influence of herbivores on population dynamics of their host plants, especially the relative roles of different types of damage, is, however, still poorly understood. Here, we present a modelling approach, including both deterministic and stochastic matrix modelling, to be used in estimating fitness effects of multiple herbivores on perennial plants. We examined the effects and relative roles of two specialist herbivores, a pre-dispersal seed predator, Euphranta connexa, and a leaf-feeding moth, Abrostola asclepiadis, on the population dynamics and long-term fitness of their shared host plant, a long-lived perennial herb Vincetoxicum hirundinaria (Asclepiadaceae). We collected demographic data during 3 years and combined these data with the effects of natural levels of herbivory measured from the same individuals. We found that both seed predation and leaf herbivory reduced population growth of V. hirundinaria, but only very high damage levels changed the growth trend of the vigorously growing study populations from positive to negative. Demographic modelling indicated that seed predation had a greater impact on plant population growth than leaf herbivory. The effect of leaf herbivory was weaker and diminished with increasing level of seed predation. Evaluation of individual fitness components, however, suggested that leaf herbivory contributed more strongly to host plant fitness than seed predation. Our results emphasize that understanding the effects of a particular herbivore on plant population dynamics requires also knowledge on other herbivores present in the system, because the effect of a particular type of herbivory on plant population dynamics is likely to vary according to the intensity of other types of herbivory. Furthermore, evaluating herbivore impact from using individual fitness components does not necessarily reflect the long-term effects on total plant fitness. © 2005 Gesellschaft für Ökologie.

Large data requirements may restrict the use of matrix population models for analysis of population dynamics. Less data are required for a small population matrix than for a large matrix because th ...

11 páginas, 3 figuras, 3 tablas, 1 dibujo.-- et al., [EN]: Although the effects of deterministic factors on population viability often are more important than stochasticity, few researchers have dealt with the effect of deterministic habitat changes on plant population demography. We assessed population viability for the perennial herb Primula veris L. and identified targets for management based on demographic data from five different habitat types representing different degrees of canopy closure. We conducted replicate studies at the border of the distribution area and in more central parts. Demographic patterns were similar between the two regions. Most study populations had a positive population growth, and only populations in late phases of forest succession showed consistently negative trends. The populations of open habitats had high seedling recruitment, and the populations of early and middle forest succession had high seed production. The importance of survival for population growth rate increased with increasing habitat closure, whereas the importance of growth and reproduction decreased. Results of the elasticity analysis suggested that the best method to manage decreasing late-successional populations is to increase survival of the largest individuals. The life-table response experiment (LTRE) analysis, however, showed that survival of the largest individuals contributed little to differences in population growth rates of different habitats, whereas seed production and growth of small individuals were more important. Moreover, direct perturbation of the performance of the largest stages showed that late-successional populations would not attain positive population growth even if the largest stages had no mortality at all. We conclude that restoration of recruitment is the only possibility for positive population growth in late-successional populations of P. veris, although the elasticities of recruitment transitions are low. Our results also suggest that retrospective demographic methods such as LTRE constitute an important and necessary complement to prospective methods such as elasticities in identifying management targets., [ES]: Aunque los efectos de factores determinísticos sobre la viabilidad poblacional a menudo son más importantes que la estocasticidad, pocos investigadores han abordado el efecto de los cambios determinísticos del hábitat sobre la demografía de poblaciones de plantas. Evaluamos la viabilidad poblacional de la hierba perenne Primula veris L. e identificamos objetivos para su gestión con base en datos demográficos obtenidos en cinco tipos de hábitat diferentes que representan diferentes grados de oclusión del dosel. Realizamos estudios replicados en el límite del área de distribución y en áreas más centrales. Los patrones demográficos eran similares en las dos regiones. La mayoría de las poblaciones estudiadas tenían un crecimiento poblacional positivo, y solo mostraron tendencias consistentemente negativas las poblaciones en fases avanzadas de sucesión del bosque. Las poblaciones en hábitats abiertos tenían alto reclutamiento de plántulas, y las poblaciones en bosques en sucesión temprana y media tenían alta producción de semillas. La importancia de la supervivencia para la tasa de crecimiento poblacional aumentó con el incremento de la oclusión del hábitat, mientras que disminuyó la importancia del crecimiento y la reproducción. Los resultados del análisis de elasticidad sugieren que el mejor método para manejar poblaciones decrecientes de etapas tardías de sucesión es el incremento de la supervivencia de los individuos más grandes. Sin embargo, el análisis de experimento de respuesta de tabla de vida (ERTV) mostró que la supervivencia de los individuos más grandes contribuyó poco a las diferencias en las tasas de crecimiento poblacional en hábitats diferentes, mientras que la producción de semillas y el crecimiento de individuos pequeños fueron más importantes. Más aun, la perturbación directa del funcionamiento de las etapas mayores mostró que las poblaciones de sucesión tardía no llegarían a tener crecimiento poblacional positivo aun si no hubiera mortalidad en las etapas mayores. Concluimos que la restauración del reclutamiento es la única posibilidad de crecimiento poblacional en poblaciones de P. veris de sucesión tardía, aunque las elasticidades de las transiciones de reclutamiento sean bajas. Nuestros resultados también sugieren que los métodos demográficos retrospectivos, como ERTV, constituyen un complemento necesario e importante de los métodos prospectivos, como las elasticidades, en la identificación de objetivos de conservación., The study was financed by World Wide Fund of Sweden, the Swedish Research Council (to K.L. and J.E), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) (to J.E.), Östersjöstiftelsen (to K.L.), and a postdoctoral grant from the Spanish Ministerio de Educación y Ciencia MEC (to M.B.G; ref. EX94 17713636).

Publisher Summary The principle of resource allocation states that resources are not sufficient to fully supply the demands of all plant functions. If resources are limited, allocation to reproduction must decrease the allocation to some other plant functions. Allocation of resources to reproduction (reproductive allocation) has implications for several study fields in biology. Early studies discussed allocation patterns in light of the evolution of life-history traits and interaction between life-history traits and population dynamics. Initial studies considered animals, but the idea was soon applied to plant ecology to explain how allocation affects plant life-history strategies and plant community dynamics. To test the principle of allocation, biologists have tried to measure the resource use of different plant functions. This task has turned out to be difficult. It is not clear which currency should be used to measure reproductive allocation. Meristems have been proposed as a currency to measure reproductive allocation. Meristems come as distinct reproductive or vegetative entities. This chapter aims to discuss whether meristem allocation can be used as a supplement or a substitute when studying reproductive allocation. It first describes the structural, developmental, and physiological background of the meristem system. It then uses a modeling approach to show theoretically how meristem allocation may affect fitness. It discusses model assumptions and reviews empirical studies that have tested allocation models and their assumptions.

Plants have two principal defense mechanisms to decrease fitness losses to herbivory: tolerance, the ability to compensate fitness after damage, and resistance, the ability to avoid damage. Variation in intensity of herbivory among populations should result in variation in plant defense levels if tolerance and resistance are associated with costs. Yet little is known about how levels of tolerance are related to resistance and attack intensity in the field, and about the costs of tolerance. In this study, we used information about tolerance and resistance against larval herbivory by the butterfly Anthocharis cardamines under controlled conditions together with information about damage in the field for a large set of populations of the perennial plant Cardamine pratensis. Plant tolerance was estimated in a common garden experiment where plants were subjected to a combination of larval herbivory and clipping. We found no evidence of that the proportion of damage that was caused by larval feeding vs. clipping influenced plant responses. Damage treatments had a negative effect on the three measured fitness components and also resulted in an earlier flowering in the year after the attack. Tolerance was related to attack intensity in the population of origin, i.e. plants from populations with higher attack intensity were more likely to flower in the year following damage. However, we found no evidence of a relationship between tolerance and resistance. These results indicate that herbivory drives the evolution for increased tolerance, and that changes in tolerance are not linked to changes in resistance. We suggest that the simultaneous study of tolerance, attack intensity in the field and resistance constitutes a powerful tool to understand how plant strategies to avoid negative effects of herbivore damage evolve.

The geographic mosaic theory of co-evolution states that evolution of interactions is driven by geographical variation in interactions between species. We investigated whether the intensity of pre-dispersal seed predation differed among nine Primula veris populations over 5 years, and whether such differences lead to geographical variation in selection on flower number. Seed predation intensity differed significantly among years and populations, and it increased with canopy closure and decreased with the density of the field layer vegetation. Individuals in open habitats also produced the highest number of flowers. Moreover, the phenotypic selection on flower number differed among years and populations. In populations of closed habitats, with high seed predation pressure, the increased number of flowers was often correlated with an increased number of damaged capsules. However, an increased flower number did not result in fewer intact fruits due to seed predation in any population.

The effect of flower and leaf removal on Primula veris was studied in two populations close to each other. Removal of both flowers and leaves resulted in decreased growth, flowering and reproduction in the next two years in both populations; there was no change in survival. In one population, removal of all flowers increased the flower number, the flower stalk length and the leaf area, and doubled the seed set in the year following the treatment. In the other population flower removal slightly decreased the seed set in the next year, while plant size did not differ from the control group. There were no significant differences in seed germinability between any of the experimental groups