bluuebunny/crossref_metadata_2025_split huggingface dataset:
A simple mechanistic model of seed dispersal, predation and plant establishment: Janzen‐Connell and beyond
Authors: NATHAN RAN , CASAGRANDI RENATO 
Published: September 2004

Summary

Although, in nature, seed dispersal usually declines with distance from the source, seedling establishment patterns are highly variable. An increase in seed survival can lead to either hump‐shaped (Janzen‐Connell (J‐C) pattern) or declining (Hubbell pattern) establishment with distance from seed source, but declining establishment can also be generated if survival decreases with distance (McCanny pattern). Pathogens and seed predators are considered to be major mortality agents structuring recruitment patterns, but it is unclear how well predation alone can explain variation in these patterns.
We introduce a simple mechanistic model showing that distance and density‐dependent seed predation can generate all of the observed recruitment patterns. Our approach provides the first mathematical reconstruction of conceptual models previously considered to be based on contrasting underlying mechanisms. Three easily measurable quantities (the proportion of seeds escaping predation at the source, and the mean distance from the source of dispersed seeds and of predators’ activity) can be used to test for consistency with the J‐C pattern. The association between recruitment patterns and plant (dispersal) and animal (predation) characteristics is robust with respect to parameter values and various functional forms.
The model shows that the J‐C pattern can occur only if the mean distance over which predators are active is lower than that over which seeds are dispersed, corresponding to a system with host‐specific, or immobile, seed predators (often invertebrates) that are restricted to areas of high seed density near adult plants, and therefore selecting for longer dispersal distances of seeds.
The Hubbell pattern is generated by the model when dispersal and predation distances are of equivalent magnitudes. The McCanny pattern emerges if more generalized, or more mobile, seed predators (often vertebrates) are attracted to the adult trees but also tend to forage farther away, thereby selecting for short dispersal distances that generate high densities needed to satiate seed predators.
The model also predicts that the total number of seeds surviving predation is lowest at intermediate distances, suggesting that distance‐dependent predation promotes either short or long dispersal distances, or both (dimorphism).
Dispersal potential in plant communities depends on environmental conditions
Authors: OZINGA WIM A. , BEKKER RENÉE M. , SCHAMINÉE JOOP H. J. , VAN GROENENDAEL JAN M. 
Published: September 2004

Summary

Local plant communities can only function within a metacommunity context if they are connected by appropriate dispersal vectors, accommodating the transport of propagules between sites. The capacity for long‐distance dispersal may be a key factor in the survival of local populations, especially in fragmented landscapes, and hence may have a large impact on local species composition. Dispersal vectors with a large efficiency for long‐distance dispersal included in this study are: water, wind, large mammals and birds.
We tested the hypothesis that variation in dispersal traits across plant communities is related to the position of the communities along major environmental gradients. This hypothesis was tested for (i) separate long‐distance dispersal vectors and (ii) multiple dispersal vectors (the number of potential long‐distance dispersal vectors per species).
To quantify linkages between dispersal traits and environmental gradients, we coupled a data base containing dispersal attributes with another data base, containing 40 000 local vegetation descriptions aggregated into 123 plant communities. For each dispersal vector, the proportions of species that have access to this vector per community (weighted trait scores) were projected along three major environmental gradients: soil moisture, nutrient availability and light availability.
The potential importance of individual dispersal vectors showed clear differences along the three environmental gradients, with the greatest differences along the light availability gradient. The differences in dispersal traits probably reflect environmental constraints on the availability or efficiency of individual dispersal vectors.
The ability to be dispersed by multiple dispersal vectors is a common phenomenon in most plant communities (an average of 2.15 vectors per species). The mean number of potential long‐distance dispersal vectors per species increases with light availability. This probably implies that plant communities differ in their response to both habitat fragmentation and habitat restoration.
Despite differences in trait spectra among communities, all dispersal syndromes are represented in nearly all communities. An important consequence of this complementarity in dispersal traits is that species within the same community may experience different connectivity.
The results emphasize the need for dispersal models based upon multiple dispersal vectors that explicitly include parameters for habitat characteristics.
The influence of spatial patterns of damping‐off disease and arbuscular mycorrhizal colonization on tree seedling establishment in Ghanaian tropical forest soil
Authors: HOOD L.A. , SWAINE M.D. , MASON P.A. 
Published: September 2004

Summary

Milicia regia (Moraceae) is a dioecious light‐demanding (Pioneer) timber tree of West Africa. Experiments in shadehouses were used to examine the influence of light and soil source (beneath and away from conspecific adults) on mortality and growth of its seedlings in relation to fungal pathogens and arbuscular mycorrhizal (AM) colonization.
The experiment in Ghana included treatments for light (2% and 20% of unshaded irradiance), three soil sources (under female, under male and 200 m distant from adults), and two different fungicide treatments.
The results showed significant effects of irradiance, soil source and fungicide on both seedling mortality and accumulated biomass. Biomass was greater and mortality reduced at higher irradiance. Fungicide application reduced mortality in 2% irradiance, but had no significant effects at 20%, although AM infection of seedlings grown in soils from beneath adults was severely reduced. Mortality was greatest in soil from beneath female trees and least in soil distant from adult conspecifics. However, biomass in 20% irradiance was greater in soil from beneath females, possibly because of enhanced AM colonization: seedlings had a significantly higher percentage root length colonized by AM fungi beneath adult conspecifics, and biomass accumulation was significantly correlated with root length colonized by AM fungi.
There were significant interactions amongst light, soil source and fungicide treatments that attest to the complexity of spatial effects on seedling establishment in tropical forest. Whilst there was clear evidence of pathogen‐mediated effects that provides support for Janzen‐Connell spacing mechanisms, and escape from the parent tree increases the chances of arriving in gaps, spatial differences in AM fungal communities may act in the opposite direction and enhance seedling growth close to adult conspecifics.
The complexity of interactions between abiotic and biotic factors and the way in which these factors can vary spatially to affect seedling recruitment may be an important factor contributing to the maintenance of tree species diversity in tropical forests.
Extensive hydrochory uncouples spatiotemporal patterns of seedfall and seedling recruitment in a ‘bird‐dispersed’ riparian tree
Authors: HAMPE ARNDT 
Published: September 2004

Summary

Initial recruitment is by far the most variable and least predictable phase of the plant life cycle. Its dynamics remain little known, particularly in complex seed dispersal systems and over multiple reproductive cycles.
Seeds of the tree Frangula alnus are usually dispersed by frugivorous birds. Mediterranean populations, however, are mostly restricted to riparian forests, and their seeds may be re‐distributed during the winter by elevated stream water flow. Strength and frequency of peak discharges vary greatly from year to year. I investigated spatiotemporal variation of initial recruitment by monitoring fruit production, seedfall and seedling emergence over 4 years along permanent transects in two F. alnus populations growing along small mountain streams in southern Spain.
Seedling abundance varied greatly among years and independently of fruit or primary seedfall abundance. Spatial distributions of both seedfall and seedling emergence were highly consistent among years. Bird‐mediated seedfall density decreased exponentially with both increasing distance from the nearest fruiting tree and the decrease of its crop size. Seedling emergence was, however, uncoupled in space from the previous year's seedfall, both across single sample points and entire 60‐m transects. Dispersal experiments with seed mimics revealed that flooding caused secondary dispersal of much of the population seed pool over several scores of metres.
Seed re‐distribution by water appears to override patterns of primary (bird‐generated) seedfall and to determine spatial patterns of seedling recruitment. Seedling emergence is, however, more stable across years than would be expected given the unpredictability of rainfall (and thus stream flow), suggesting that seed deposition may be primarily determined by relatively stable microsite characteristics.
The dynamics of seed rain patterns are of critical importance for plant population demography and spatial structures. The finding that even complex, multistep dispersal systems may produce remarkably consistent year‐to‐year distributions of recruits has important implications for the interpretation of long‐term patterns of riparian plant regeneration at the landscape level and resulting conservation management.
Effect of spatial scale on factors limiting species distributions in dry grassland fragments
Authors: MÜNZBERGOVÁ ZUZANA 
Published: September 2004

Summary

Distribution of plant species in fragmented landscapes is the result of both seed and site availability. Little is known about how their relative importance differs at different spatial scales.
I sowed seeds of eight dry grassland species into 22 localities that differed in occupancy by these species and followed seedling establishment over 3 years. I compared the number of emerging seedlings at three scales: between previously occupied and previously unoccupied localities, between occupied and unoccupied blocks within occupied localities, and between plots with and without seed addition within occupied blocks.
At the two larger scales, I also studied the relationship of the number of seedlings and of the distributions of adult plants to environmental factors.
Both seed and site availability are important in structuring the distribution of these species, but site availability becomes less important with increasing spatial scale. The intensity of this effect is, however, species specific.
The relationship between environmental factors and pattern of species distribution is also clearly scale dependent, and differs between seedlings and adults. Whilst abiotic factors are the main determinants of seedling distribution, the occurrence of adult individuals is best predicted by the occurrence of other species. This suggests that the present distribution of species in the landscape is determined mainly by historical factors.
Conclusions based on the importance of seed and site availability for species distribution in natural communities at one scale cannot be extrapolated to other scales. Only comparisons on multiple scales can provide a full understanding of factors affecting species distribution at landscape level.
An evaluation of alternative dispersal functions for trees
Authors: GREENE DAVID F. , CANHAM CHARLES D. , COATES K. DAVID , LEPAGE PHILIP T. 
Published: September 2004

Summary

We compared three commonly used empirical seed/seedling dispersal functions for trees (lognormal, 2Dt, and two‐parameter Weibull) by analysis of published studies where the location of the source is known, as well as by inverse modelling within an old growth hardwood forest in southern Quebec. Almost all the species were wind‐dispersed.
For the discrete source studies, the lognormal was clearly superior, while for the inverse modelling the performance of the three dispersal functions was somewhat more even. We speculate that collisions with boles spuriously enhanced the likelihood of the 2Dt and the Weibull with inverse modelling, as both these functions assume that the greatest seed/seedling density will occur at the base of the maternal parent bole.
We conclude that the lognormal function is to be preferred because, as well as providing a framework for mechanistic interpretation, it tends to provide a closer approximation to observed dispersal curves.
We also argue that mean distances travelled by seed crops are far more extensive than indicated by previous studies that used the Weibull function.
Identifying and modelling the determinants of woody plant invasion of lowland heath
Authors: MANNING P. , PUTWAIN P. D. , WEBB N. R. 
Published: September 2004

Summary

The invasion of Betula spp. represents the moment of transition between European lowland heath and scrub ecosystems. We hypothesized that Betula invasion was controlled by a multivariate threshold, comprising factors that may be subdivided into seed and safe‐site limitations, and that phosphorus availability was a key determinant of the Betula safe‐site.
We performed a multifactorial field experiment in which seed rain, P‐availability and disturbance were manipulated. All treatments had significant effects on Betula seedling densities, with seed availability proving the single greatest limitation. P addition emerged as having highly significant effects 4 and 12 months after germination. Disturbance had an initially large positive effect that dwindled across time.
Detailed descriptions of seedling density data were achieved by converting two factorial variables (seed rain and P availability) to a continuous form, including numerous covariates, and producing ‘minimum adequate’ generalized linear models (MAMs). These provided accurate descriptions of the data (explained deviance typically > 70%) and delimited site conditions where transition was likely.
Seed availability remained the most important factor, but the increased number of parameters in models describing densities of more mature seedlings suggested a temporal accumulation of recruitment limitations. Statistical modelling allowed for the subdivision of disturbance effects into those associated with a reduction in vegetation densities and the remaining ‘direct’ effects, e.g. soil disturbance, which shifted over time from being positive to negative. The results also support the hypothesis that soil phosphorus sorption capacity (PSC) determines heath–scrub transition as many of the identified determinants are controlled, either directly or indirectly, by PSC.
The study demonstrates that a combination of experimental and statistical modelling approaches can provide a detailed description of the factors controlling early stage invasion and may therefore have considerable utility in ecosystem management. Although site specific, the models illuminate the mechanisms by which many larger scale processes, e.g. burning and grazing, regulate the persistence of lowland heath ecosystems.
Plant community development is affected by nutrients and soil biota
Authors: DE DEYN G. B. , RAAIJMAKERS C. E. , VAN DER PUTTEN W. H. 
Published: September 2004

Summary

Plant community development depends to a great extent on the availability of soil nutrients, but recent studies underline the role of symbiotic, herbivorous and pathogenic soil biota. We tested for interactions between these biotic and abiotic factors by studying the effects of additional nutrients and the removal of soil biota on the replacement of grassland plant species typical of different successional stages.
Species representing each of the early, mid and target phases of secondary succession in a grassland community (four per phase) were grown in mid‐successional grassland soil. The mixed plant communities were grown in sterilized and non‐sterilized soil, at three nutrient supply levels. The distribution of shoot biomass over the different plant species, and the total root biomass, were determined, as well as the composition of nematode and microarthropod communities and soil decomposition rates.
The effect of nutrient supply on plant community composition depended on soil sterilization. In sterilized soil, the plant community was initially dominated by grasses that increased in dominance even without fertilization. In non‐sterilized soil, the plant community was more diverse and grass dominance decreased over time, except with high fertilization. Fertilization enhanced the productivity of the plant community in sterilized and, to a greater extent, in non‐sterilized soil.
The abundance of root‐feeding nematodes was positively related to increased root biomass, pointing to a strong bottom‐up control. Increased levels of nutrient supply were associated with reduced abundance of omnivorous nematodes, the cause of this reduction being less clear. Increased soil fertility altered the functional diversity of the soil nematode community, which might, in the longer term, also affect their feedback effects on the plant community.
Increased nutrient supply reduced soil decomposition activity in the non‐sterilized soil, but not in the sterilized soil.
Our results imply that soil biota may reduce the effects of nutrient supply on plant dominance. Incorporating the effects of soil biota on plant species interactions into studies on succession, plant species diversity and restoration may therefore considerably increase our understanding of the observed plant community patterns.
Effect of dispersal capacity on forest plant migration at a landscape scale
Authors: TAKAHASHI KANAKO , KAMITANI TOMOHIKO 
Published: September 2004

Summary

We studied the effects of seed dispersal mode and seed mass on the migration patterns of woody and herbaceous forest species in an artificial pine forest band growing on a former sand dune. Seven sites in the artificial forest, at least 44 years old, were selected at different distances from an adjacent natural forest (0.1–17.4 km).
Both the species richness and the abundance of forest species decreased with increasing distance from the natural forest, indicating that the migration of forest species is limited by seed dispersal. Plants using different seed dispersal modes showed differences in migration rate.
Ingested and adhesive species migrated into the artificial forest with the most success. In contrast, almost all the species utilizing other dispersal mechanisms (wind, hoarding or no dispersal mechanism) migrated only into sites near to the natural forest. This is likely to be due to low dispersal capacities. Ant‐dispersed species were not found at all in the artificial forest.
Migration distances were calculated for 43 species with a frequency of ≥ 5% in at least one site in the artificial forest. Distances were based on the occurrence of the individual of each species furthest from the natural forest, and on the maximum abundance of that species in the artificial forest. The migration distances of the species did not correlate with their seed mass.
The dispersal efficiency is an important factor in migration of forest species on a landscape scale, and the migration ability is affected by dispersal mode rather than seed mass.
Consistency of plant species and trait responses to grazing along a productivity gradient: a multi‐site analysis
Authors: PAKEMAN ROBIN J. 
Published: September 2004

Summary

Studies of the responses of communities to land use or climate change at a functional rather than species level have used species traits as response or effect variables to enable generalization between different communities and biogeographical regions. Data from 10 published experiments on semi‐natural and agricultural grasslands in Scotland, and from published information on plant traits, were used to determine whether (a) species and trait attributes behave consistently with respect to changing grazing intensity at sites of different productivity and (b) whether species and attribute responses to grazing were affected by site productivity.
Only 9 out of 22 species common enough to show a consistent response to grazing did so. For example, Deschampsia flexuosa and Molinia caerulea declined when grazing intensity increased, whilst Anthoxanthum odouratum and Cerastium fontanum increased. A similar proportion (12/29) of traits behaved consistently between studies.
Increased grazing intensity was accompanied by an increase in species with a ruderal strategy, an annual life history, seasonal regeneration by seed, flowering and seed dispersal early in the season, rosette habit, higher requirement for light and a lower minimum height.
The response of five species was modified by site productivity. In four cases, the effect was to modulate the rate of response to grazing change. In contrast, Nardus stricta increased with grazing at low productivity sites, but decreased at high productivity sites. Many more traits (22), including attributes related to life history, life form, and vegetative and sexual reproduction, showed a response to grazing modulated by productivity. Eight of these changed in a complex manner, akin to that of N. stricta.
The response of some species and traits to grazing appears predictable. However, for some species and many traits either the rate or the direction of response is controlled by the productivity of the vegetation.
Competitive Multifacility Location on Networks: the (r∣Xp)‐Medianoid Problem
Authors: Suárez‐Vega Rafael , Santos‐Peñate Dolores R. , Dorta‐González Pablo 
Published: September 2004

Abstract.  We investigate the (r∣Xp)‐medianoid problem for networks. This is a competitive location problem that consists of determining the locations of r facilities belonging to a firm in order to maximize its market share in a space where a competitor is already operating with p facilities. We consider six scenarios resulting from the combination of three customer choice rules (binary, partially binary, and proportional) with two types of services (essential and unessential).Known discretization results about the existence of a solution for the set of nodes are extended. Some examples and computational experience using heuristic algorithms are presented.