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Jacquemyn H.,Catholic University of Leuven | Brys R.,Research Institute for Nature and Forest | Jongejans E.,Radboud University Nijmegen
Ecology | Year: 2010

Seed production and seedling recruitment are thought to be of minor importance in determining population dynamics and long-term viability in long-lived perennial plants. Seed addition experiments, on the other hand, have amply shown that supplemental addition of seeds almost always, irrespective of longevity, results in increased seedling recruitment. Any change in the environment that affects fruit and seed production can thus be expected to affect seedling recruitment, but the extent to which increased fruit and seed production affect overall population dynamics remains relatively unknown. In this paper, we present demographic data of six populations of the long-lived woodland orchid Orchis purpurea that were monitored for seven consecutive years (2002-2008) occurring in two contrasting light environments. We use a nested life table response experiment (LTRE) at the vital rate level to disentangle the relative contributions of each of six annual transitions, six sites, and two light environments on the population dynamics of this species and to determine vital rate variations that contributed most to variation in population growth rate. Population growth rates (λ) were significantly higher in the light environment than in the shaded environment (average λ = 0.9930 and 1.0492 in the shaded and light environment, respectively). The LTRE analysis showed that variation in fecundity and, to a lesser extent, variation in growth made the largest total contributions to variation in λ, whereas the contributions of variation in survival were almost negligible. Fruit production was two times larger and the net reproductive rate (R0) was approximately six times higher in the light environment than in shaded areas, suggesting that variables related to reproduction are the key drivers of population dynamics of this long-lived orchid species in different light environments. Our results indicate that light is an important factor affecting population dynamics of Orchis purpurea and illustrate that, even in long-lived species, flower and seed production can have important effects on the population dynamics. © 2010 by the Ecological Society of America.

Jacquemyn H.,Catholic University of Leuven | Brys R.,Research Institute for Nature and Forest | Jongejans E.,Radboud University Nijmegen
Journal of Ecology | Year: 2010

1. In woodland herbs, the probability of flowering and costs associated with reproduction may strongly depend on environmental context (shade vs. light habitats) and on plant size. This may be particularly true for tuberous orchids that inhabit woodlands, as the amount of incoming radiation and total leaf area strongly determine photosynthetic capacity and hence the amount of carbohydrates that can be relocated to below-ground storage organs that form next year's rosette and flowering stalk. 2. To fully comprehend the impact of size-dependent reproduction on population dynamics under varying light conditions, life cycle models should therefore include plant size in a continuous manner. In this study, annual changes in plant size and demographic behaviour of the tuberous perennial orchid Orchis purpurea were monitored during seven consecutive years (2003-2009) in open and shaded woodland. Integral projection models (IPMs) and life table response experiments (LTRE) were used to investigate the extent to which variation in plant size affected the overall population dynamics of this species and to decompose differences in population growth rates between populations of open and shaded woodland into contributions from growth, survival and reproduction. 3. Both plants in shaded and light environments needed to be a certain size to initiate flowering, but this threshold size was almost three times as large in shaded environments as in light environments. Plants in open woodlands flowered more frequently over the years, showed less size regression after flowering and produced significantly more fruits than plants in shaded environments, resulting in significantly larger population growth rates. 4. Our life cycle models revealed that costs of reproduction, measured at the population-level, were small in the light environment, and more than buffered by the increase in survival of flowering plants compared to non-flowering plants. In the shade environment, however, the costs of reproduction were significant and made the difference between a stable (current) and a growing (without reproduction costs) population. 5. Synthesis. Light penetration to the soil is a key variable determining population dynamics of woodland orchids. Our analyses show that differences in vital rates related to size-dependent reproduction (flowering) and growth are essential drivers of changes in orchid population dynamics in different light environments. The combination of IPMs and LTREs thus proves to be very useful when studying the fitness consequences of size- and context-dependent phenomena like flowering strategies and costs of reproduction. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

Brys R.,Research Institute for Nature and Forest | Brys R.,Ghent University | Jacquemyn H.,Catholic University of Leuven
Functional Ecology | Year: 2012

Human-induced impoverishment of pollinator faunas may affect plant-pollinator interactions and limit pollen availability. Under these conditions, chronic outcross pollen limitation is expected to select for floral characters that maintain seed production, including autonomous selfing. In this study, the impact of anthropogenic disturbances of the pollinator environment of the short-lived Centaurium erythraea on mating patterns was investigated. First floral traits and the capacity for autonomous selfing were compared between two contrasting pollinator environments. In addition, transplantation experiments were combined with hand-pollination and emasculation treatments to assess the extent of pollen limitation and the contribution of autonomous selfing to total seed production in these pollinator environments. Under severe pollinator impoverishment, C. erythraea produced fewer and smaller flowers that showed no herkogamy and strongly reduced P/O ratios. The capacity for autonomous selfing was 36·1% higher in these pollinator-limited environments than in more natural, pollinator-rich environments, where plants developed more, larger and markedly herkogamous flowers. When assigned to the pollinator-rich environments, plants from pollinator-limited populations showed significantly higher outcross pollen limitation compared with the original plants. In contrast, plants from pollinator-rich environments assigned to pollinator-poor populations did not experience higher pollinator-mediated seed production and showed lower total seed production than plants originally occurring in these pollinator-limited environments. These results demonstrate that human-induced pollen limitation selects for selfing as a means of reproductive assurance, whereas in the pollinator-rich environments, traits that support outcrossing are favoured. © 2011 The Authors. Functional Ecology © 2011 British Ecological Society.

Brys R.,Research Institute for Nature and Forest | Brys R.,Ghent University | Jacquemyn H.,Catholic University of Leuven
Annals of Botany | Year: 2011

Background and Aims Reproductive assurance through autonomous selfing is thought to be one of the main advantages of self-fertilization in plants. Floral mechanisms that ensure autonomous seed set are therefore more likely to occur in species that grow in habitats where pollination is scarce and/or unpredictable. Methods Emasculation and pollen supplementation experiments were conducted under laboratory conditions to investigate the capacity for, and timing of autonomous selfing in three closely related Centaurium species (Centaurium erythraea, C. littorale and C. pulchellum). In addition, observations of flower visitors were combined with emasculation and pollen addition experiments in natural populations to investigate the degree of pollinator limitation and pollination failure and to assess the extent to which autonomous selfing conferred reproductive assurance.ResultsAll three species were capable of autonomous selfing, although this capacity differed significantly between species (index of autonomous selfing 0·55 ± 0·06, 0·68 ± 0·09 and 0·92 ± 0·03 for C. erythraea, C. littorale and C. pulchellum, respectively). The efficiency and timing of autogamous selfing was primarily associated with differences in the degree of herkogamy and dichogamy. The number of floral visitors showed significant interspecific differences, with 1·6 ± 0·6, 5·4 ± 0·6 and 14·5 ± 2·1 floral visitors within a 2 × 2 m2 plot per 20-min observation period, for C. pulchellum, C. littorale and C. erythraea, respectively. Concomitantly, pollinator failure was highest in C. pulchellum and lowest in C. erythraea. Nonetheless, all three study species showed very low levels of pollen limitation (index of pollen limitation 0·14 ± 0·03, 0·11 ± 0·03 and 0·09 ± 0·02 for C. erythraea, C. littorale and C. pulchellum, respectively), indicating that autonomous selfing may guarantee reproductive assurance. Conclusions These findings show that limited availability of pollinators may select for floral traits and plant mating strategies that lead to a system of reproductive assurance via autonomous selfing. © 2011 The Author.

Louette G.,Research Institute for Nature and Forest
Wildlife Research | Year: 2012

Context The control of invasive alien species is essential for securing native biodiversity. As for the American bullfrog, Lithobates catesbeianus (Shaw 1802), suspected to cause ecological damage around large parts of the globe, comprehensive management techniques are currently absent. Aims To fill this gap, opportunities arising from biomanipulation of permanent water bodies inhabited by fish were explored. Methods A multi-annual experiment was performed in small and shallow ponds, and effects of complete drawdown (with amphibian and fish removal) and predation (introduction of originally occurring native northern pike, Esox lucius) on non-indigenous bullfrogs were investigated. Key results The presence of pike lead to a strong decline in bullfrog tadpole numbers, whereas no effect of drawdown was observed. Also, communities receiving pike harboured substantially less small and mostly planktivorous fish species (e.g. pumpkinseed, Lepomis gibbosus, and topmouth gudgeon, Pseudorasbora parva). Conclusions The reduction in bullfrog tadpoles may be assigned to both direct and indirect effects induced by pike. First, direct pike predation on tadpoles was observed. Second, as the occurrence of macroinvertebrate-feeding pumpkinseed was low in the presence of pike, the indirect effect of predation by macroinvertebrates on tadpoles may significantly increase, leading to tadpole decline. Implications Biomanipulation of permanent water bodies inhabited by fish can thus be regarded as a candidate for effective and sustainable control of invasive bullfrog. Piscivorous fish introduction may be applied in the specific type of water body, but requires careful consideration of the indigenous status of the introduced species, angling purposes, or specific nature values. © 2012 CSIRO.

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