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The Park Grass Experiment (PGE) is the longest-observed set of experimental plant communities in existence. Although the gross composition of the vegetation was at equilibrium over the 60-yr period from 1920 to 1979, annual records show that individual species exhibited a range of dynamics. We tested two hypotheses to explain why some species initi...
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... of the contrast sets each con- tained a triplet of related species chosen to include one persistent-increase species, one outbreak species, and one control species. Because there were only seven outbreak species present in the data set, an eighth comparison con- sisted of just one control species and one persistent- increase species (table 1); hence, 23 species were used in all. All species except Bromus hordeaceus were perennial. ...
Citations
... Thus, self-thinning and biomass-density relationships in benthic animals follow the same rules as in plant populations (Norberg 1988;Fréchette & Lefaivre 1990Fréchette et al. 1992;Linares et al. 2008;O'Gorman & Emmerson 2011). In addition, interspecific competition substantially reduces plant fecundity and seed recruitment (Miriti et al. 2001;Silvertown et al. 2002;Fréville & Silvertown 2005). Mortality selection on plants is probably strongest at the seed and seedling stages (Huey et al. 2002). ...
... Matrix population models are helpful tools in plant population ecology, as they provide a common conceptual framework for comparative research (Nguyen et al., 2019;Salguero-G omez & de Kroon, 2010;Salguero-G omez & Plotkin, 2010;Silvertown et al., 1993). The growing number of studies using comparative approaches with matrix population models (Salguero-G omez et al., 2015) has allowed linking specific vital rates (Adier et al., 2014;Franco & Silvertown, 2004) and stages in ecological successional gradients (Silvertown et al., 2002), life history evolution (Burns et al., 2010), population dynamics of native vs. invasive plant species (Ramula et al., 2008) or senescence (Jones et al., 2014), among others. We focused on the vital rates of seed bank survival and seedling recruitment to examine their relative effects on the overall population growth rates (λ). ...
The dynamics of plant populations are often limited by the early stages in their life cycles. However, information regarding seed bank dynamics and how these may influence the whole life cycle of plant species is remarkably scarce or not considered explicitly. This lack of knowledge is due mainly to the challenges in quantifying seed vital rates. Studies of arid land plant species have historically been focused on the drivers of sporadic recruitment. However, little attention has been given to the demographic consequences of early developmental stages, and how seed banks affect their dynamics. Here, we evaluate the effects of seed bank survival and seedling recruitment vital rates on the population dynamics and viability of 12 columnar cacti species. Recent evidence suggests that cacti seeds may remain viable for the short‐term. We assess how changes in the vital rates of these processes and the inclusion of a seed bank affect population growth rate (λ). We found that a seed bank in the examined matrix population models significantly increased λ as well as the vital rate elasticities of λ to growth and fecundity, whereas that of overall survival decreased. Our numerical simulations showed that seed survival had a more considerable effect on λ than seedling recruitment and establishment. We suggest that the seed bank may explain the structure and population dynamics. Thus, we reconsider that this early stage in demographic models will generate more informed decisions on the conservation and management of columnar cacti. This manuscript reports results on the evaluated effects of seed bank survival and seedling recruitment vital rates on the population dynamics and viability of 12 columnar cacti species.
... A general lesson from our study is that passive restoration of a desirable, historically dominant plant species through growth, reproduction, and expansion following planting at low density will depend on provision of appropriate conditions for the increase of that species in the context of the broader plant community (Silvertown et al. 2002). Studies of perennial grass population dynamics within natural communities or competition experiments have found that life-history characteristics of the focal species can determine whether it increases or decreases under specific environmental conditions, including fire regime (Short et al. 2003), grazing pressure (Wesuls et al. 2013), soil nutrient levels (Venterink & Güsewell 2010), light and water resources (Chang & Smith 2014;Altesor et al. 2017), soil microbial associations (Bonkowski & Roy 2005), and other factors. ...
Aristida beyrichiana (wiregrass) is a foundation bunchgrass species in many southeastern U.S. native pine communities, but it has been dramatically reduced in extent. The potential for reintroduced wiregrass to reproduce and spread is not well studied because of its slow growth and limited conditions for successful reproduction. We present a case study where tussocks of wiregrass were transplanted and recensused 18 and 37 years later to study their population dynamics. We remeasured a subset of tussocks to estimate diameter growth over two years. With frequent prescribed fires (1–3 year intervals, about half in April–July when flowering is induced), the initial population of 160 tussocks increased to 1,199 through seed dispersal and clonal fragmentation, and the total basal area approximately tripled. Relationships among tussock density, diameter, and basal area per m² and their changes over time suggest density‐dependent regulation of population structure, possibly from intraspecific competition and competitive exclusion. Tussock diameter growth averaged 0.9 cm per year over a two year period and was independent of initial diameter. This study, the longest of a wiregrass population to date, suggests that a low‐density population established in native soil types has a slow but robust tendency to reproduce by seed and expand if provided frequent fire, including April–July burns, in a high light environment without soil disturbance. Wiregrass can be characterized as a competitive, late‐successional, dominant species in stable, climax‐like native savannas, promising long‐term success under appropriate conditions as part of restoration efforts.
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... Matrix population models are helpful tools in plant population ecology, as they provide a common conceptual framework for comparative research (Silvertown et al., 1993;Salguero-Gómez and de Kroon, 2010;Salguero-Gómez and Plotkin, 2010;Nguyen et al., 2019). The growing number of studies using comparative approaches with matrix population models (Salguero-Gómez et al., 2015) has allowed linking specific vital rates (Franco and Silvertown, 2004;Adier et al., 2014) and stages in ecological successional gradients (Silvertown et al., 2002), life history evolution (Burns et al., 2010), population dynamics of native vs. invasive plant species (Ramula et al., 2008), or senescence (Jones et al., 2014), among others. We focused on the vital rates of seed bank survival and seedling recruitment to examine their relative effects on the overall population growth rates (λ). ...
The dynamics of plants populations are often limited by the early stages in their life cycles. The question if the columnar cacti have or not a seed bank in predictable environments. Yet, information regarding seed bank dynamics and how these may influence the full life cycle of plant species is remarkably scarce or ignore. This lack of knowledge is mostly due to the challenges in quantifying seed vital rates. Studies of arid land plant species have historically been focused on the drivers of sporadic recruitment. However, little attention has been given to the demographic consequences of early developmental stages, including seed banks. Here, we evaluate the effects of seed bank survival and seedling recruitment vital rates on the population dynamics and viability of 12 columnar cacti species, recent evidence suggests that cacti seeds may remain viable for the short-term. We assess how changes in the vital rates of these processes, and the inclusion of a seed bank affect population growth rate ( λ ). We found that a seed bank in the examined matrix population models significantly increased λ as well as the vital rate elasticities of λ to growth and fecundity, whereas that of overall survival decreased. Our numerical simulations showed that seed survival had a larger effect on λ than seedling recruitment and establishment. We suggest that seed bank may explain the structure and population dynamics. Thus, we argue reconsider that this early stage in demographic models will generate more informed decisions on the conservation and management of columnar cacti.
... Second, we found that Grime's CSR strategies are related to mating system in two independent ways. On one hand, on the CR edge of the triangle representing a variation of competitiveness, ruderal selfers were replaced by more competitive outcrossers (Table 3a), as observed both at intraspecific and interspecific level along ecological successions (Cheptou et al. 2002, Rydin and Borgegard 1991, Silvertown et al. 2002. On the other hand, there was no increasing outcrossing along the orthogonal index of stress-tolerance (Table 3b), and mixed mating was frequent in most stress-tolerant species (Table 2). ...
A number of plant traits influence the success of fertilization and reproduction in plants. Collectively these traits represent ecological syndromes that are of evolutionary significance. However, while an
association between mating system and colonizing ability has been proposed, the existence of a broader relationship between mating system and a species' position in ecological succession has not been extensively investigated. Grime’s CSR theory stresses that an ecological succession can
involve changes from colonizing to either competitive or stress-tolerant strategies. How distinct dimensions of competitiveness and stress tolerance covary with mating systems has still not been considered. We designed a comparative approach to evaluate the link between mating system, life
form and CSR strategies for 1,996 herbaceous and woody species. We found that CSR strategies are significantly related to mating systems. Ruderal species –colonizers in early succession– were mostly selfers while more competitive species were more often outcrossers. On the other hand,
greater physiological stress tolerance was associated with mixed mating systems. Outcrossing is classically expected to be advantageous for most life history strategies other than colonizers, but we suggest that reproductive assurance can counterbalance this effect in stressful environments where populations are sparse and pollinators are rare. Therefore, our results emphasize that competition and abiotic stresses are not equivalent selective pressures on the evolution of mating systems. Finally, we found plant life span to convey additional information on mating system variation, supporting its role for mating system evolution. These findings encourage further investigation of the evolutionary role of ecological strategies as syndromes of traits and suggest that the emergence of large databases of plant traits will help address the major evolutionary hypotheses on such syndromes.
... The Park Grass Experiment (PGE) at Rothamsted Research, Harpenden, UK, is the oldest continuous ecological experiment in the UK, with work conducted on long-term plant population dynamics over many years (Silvertown et al. 2002). Plant species within the PGE have shown a range of dynamics including: increases (e.g. ...
... This paper investigates the hypothesis presented by Silvertown et al. (2006) that P. hysterium has a regulatory influence on its host population dynamics and that this relationship is density-dependent (Silvertown et al. 2002). This assessment is undertaken by presenting data relating to the long-term population dynamics of the system in the PGE and attempting to obtain information on pathogen-induced mortality through the use of inoculation experiments. ...
... The rate of field mortality in T. pratensis is reported as 0.5 within season and 0.88 between seasons (Mahesh et al. 1996), which are within the range that will lead to cycling in the plant population. The host population in the PGE increases and decreases over a 60-yr-period (Silvertown et al. 2002) which is longer than predicted in the basic model; but as with the detailed observations between 1995 and 2008 of T. pratensis there is a 2-yr-delay in the relationship between the incidence of susceptible plants and the resulting incidence of infectious individuals within the longer cycles. The survey data demonstrates the outbreak nature of both healthy and infected T. pratensis and thus indicates that neither population reaches a high endemic steady-state. ...
Population dynamics of the biennial plant Tragopogon pratensis have been monitored in the Park Grass Experiment at Rothamsted Research, Harpenden, UK, over many years. Observations of diseased T. pratensis, systemically infected by the autoecious demicyclic rust Puccinia hysterium, were made over the period 1995-2008, and confirmed an outbreak pattern of dynamics, characterised by an increase to a relatively high incidence followed by a reduction to low almost indiscernible levels. An epidemiological model was developed taking into account the biennial habit of the host plant, and the systemic nature of infection during the winter period, and the partial sterilisation of infected second year plants. Seedling emergence rate and natural mortality between seasons and within season were key parameters affecting host performance. The transmission rate between infected second year plants and susceptible first year seedlings, and the probability that the fungus would survive the winter systemically as mycelium producing aecia and telia on emerging second year plants, were key parameters associated with pathogenicity. Furthermore the possibility of pathogen-induced additional mortality was modelled. The model predicted that outbreak dynamics of T. pratensis would occur with high pathogenicity and medium or high host performance. In the former case the population dynamics would be cyclical with, in some cases, infected plants going to extinction. In the latter case both host and pathogen would go to extinction. The model predicted that the two pathogenicity parameters were critical in determining whether the pathogen would invade a healthy population; whereas pathogen-induced mortality had little influence, a result also obtained in some limited potted plant experiments. Fitting the model to the field data indicated that there was little or no density-dependence in seedling emergence rate, and again that pathogen-induced mortality played little role in the observed population dynamics. (C) 2012 Elsevier Ltd and The British Mycological Society. All rights reserved.
... The binary classification (presence or absence) of SI may affect the assumed average outcrossing rates of species. Conventionally, species that are classified as SI are considered, along with dioecious species, to be obligately outcrossing (e.g., Silvertown et al. 2002). This assumption may result in an underrepresentation of SI species in the outcrossing rate literature due to biases against measuring the outcrossing rate of SI species . ...
Self-incompatibility is expressed by nearly one-half of all angiosperms. A large proportion of the remaining species are self-compatible, and they either outcross using various contrivances or self-fertilize to some extent. Because of the common occurrence of populations and individuals with intermediate levels of self-incompatibility, categorization of the expression of self-incompatibility as an approximately binary trait has become controversial. We collect a widely reported index (index of self-incompatibility [ISI]) used to asses the strength and variation of self-incompatibility from over 1200 angiosperm taxa. Its distribution is bimodal and positively associated with outcrossing rate, albeit with a weak relationship within self-compatible taxa. A substantial fraction of species has intermediate mean values of ISI. Their occurrence can be caused by segregating ephemeral self-compatible mutations, averaging artifacts, and experimental biases, in addition to the often invoked stabilizing selection acting on the expression of self-incompatibility. Selection may also generally favor taxa with high ISI values through increased lineage birth and death rates, and it may counter lower level selection advantages within taxa expressing intermediate and low values of ISI. Such a null hypothesis is nearly universally overlooked, despite the fact that it could adequately explain the observed distribution of mating and breeding systems.
... Anthoxanthum odoratum is wind pollinated and outcrossing (Silvertown et al. 2002) and these facts, combined with the small size of the PGE, mean that there is a high potential for pollen-mediated gene flow; as a result, nuclear genetic differentiation (via seeds and pollen) should be lower than chloroplast genetic differentiation (largely via seeds). Nevertheless, our data show that in the majority of cases pollen flow is similar to, or lower than, seed flow. ...
The spatial genetic structure of plant populations is determined by a combination of gene flow, genetic drift, and natural
selection. Gene flow in most plants can result from either seed or pollen dispersal, but detailed investigations of pollen
and seed flow among populations that have diverged following local adaptation are lacking. In this study, we compared pollen
and seed flow among 10 populations of sweet vernal grass (Anthoxanthum odoratum) on the Park Grass Experiment. Overall, estimates of genetic differentiation that were based on chloroplast DNA (cpDNA) and,
which therefore resulted primarily from seed flow, were lower (average FST = 0.058) than previously published estimates that were based on nuclear DNA (average FST = 0.095). Unlike nuclear DNA, cpDNA showed no pattern of isolation by adaptation; cpDNA differentiation was, however, inversely
correlated with the number of additions (nutrients and lime) that each plot had received. We suggest that natural selection
is restricting pollen flow among plots, whereas nutrient additions are increasing seed flow and genetic diversity by facilitating
the successful germination and growth of immigrant seeds. This study highlights the importance of considering all potential
gene flow mechanisms when investigating determinants of spatial genetic structure, and cautions against the widespread assumption
that pollen flow is more important than seed flow for population connectivity in wind-pollinated species.
... stomata. Telia, bearing teliospores on localised mycelium, are then produced (Wilson & Henderson 1966;Scott & Chakravorty 1982;Cummins & Hiratsuka 1983). ...
... T. pratensis has been present at very low densities (typically <0.1 %) on many of the non-acidified plots, but in 1993 the abundance of T. pratensis on the limed parts of one of the plots accounted for 18 % of the plot biomass. When T. pratensis was at higher density in plots, there was also a high level of rust infection, thought to be P. hysterium, a relationship described as being host densitydependent (Silvertown et al. 2002). ...
Analysis of seeds collected from rust (Puccinia hysterium) infected and uninfected Tragopogon pratensis, located within the Park Grass Experiment at Rothamsted Research, has shown a significant difference in the number of seeds produced and also in the subsequent number of successful germinations between seeds set by infected and uninfected plants. This supports the hypothesis that P. hysterium significantly suppresses reproduction in T. pratensis. Furthermore, seeds from infected individuals have significantly shorter pappi and seed mid-lengths whilst having no significant difference in seed mass, indicating that seeds from infected hosts have altered growth form.
... Direct, repeated observations (e.g. 60 through historical photography or long-term plot studies; del Moral 2007) began formally with studies of dunes in Denmark (Warming 1895) and Michigan (USA; Cowles 1899), and such observations provide the best source of evidence about temporal changes in plant and soil biological communities over years to decades. However, few studies extend beyond several 64 decades in duration (but see Chapin et al. 1994;Webb 1996;Whittaker et al. 1999;Walker et al. 2001;Silvertown et al. 2002;Meiners et al. 2007), so indirect measures are needed to determine the age successional stages and reconstruct historical vegetation or soil conditions over longer time scales. The most frequently used indirect approach for measuring temporal dynamics 68 involves the use of chronosequences and associated space-for-time substitution which represents concepts. ...
1. Chronosequences and associated space‐for‐time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time‐scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development.
2. Chronosequences are appropriate to study plant succession at decadal to millennial time‐scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time‐scales of centuries to millennia, sometimes independently of their application to shorter‐term plant and soil biological communities.
3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach.
4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species‐rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages.
5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences.
