Quantifying seed dispersal kernels from truncated seed-tracking data
Hirsch, B.T. ; Visser, M.D. ; Kays, R. ; Jansen, P.A. - \ 2012
Methods in Ecology and Evolution 3 (2012)3. - ISSN 2041-210X - p. 595 - 602.
tropical forests - plant-populations - spatial-patterns - wind dispersal - rain-forest - shadows - consequences - recruitment - dependence - behavior
1. Seed dispersal is a key biological process that remains poorly documented because dispersing seeds are notoriously hard to track. While long-distance dispersal is thought to be particularly important, seed-tracking studies typically yield incomplete data sets that are biased against long-distance movements. 2. We evaluate an analytical procedure developed by Jansen, Bongers & Hemerik (2004) to infer the tail of a seed dispersal kernel from incomplete frequency distributions of dispersal distances obtained by tracking seeds. This ‘censored tail reconstruction’ (CTR) method treats dispersal distances as waiting times in a survival analysis and censors nonretrieved seeds according to how far they can reliably be tracked. We tested whether CTR can provide unbiased estimates of longdistance movements which typically cannot be tracked with traditional field methods. 3. We used a complete frequency distribution of primary seed dispersal distances of the palm Astrocaryum standleyanum, obtained with telemetric thread tags that allow tracking seeds regardless of the distance moved. We truncated and resampled the data set at various distances, fitted kernel functions on CTR estimates of dispersal distance and determined how well this function approximated the true dispersal kernel. 4. Censored tail reconstruction with truncated data approximated the true dispersal kernel remarkably well but only when the best-fitting function (lognormal) was used. We were able to select the correct function and derive an accurate estimate of the seed dispersal kernel even after censoring 50–60% of the dispersal events. However, CTR results were substantially biased if 5% or more of seeds within the search radius were overlooked by field observers and erroneously censored. Similar results were obtained using additional simulated dispersal kernels. 5. Our study suggests that the CTR method can accurately estimate the dispersal kernel from truncated seed-tracking data if the kernel is a simple decay function. This method will improve our understanding of the spatial patterns of seed movement and should replace the usual practice of omitting nonretrieved seeds fromanalyses in seed-tracking studies
Importance of regional species pools and functional traits in colonization processes: predicting re-colonization after large-scale destruction of ecosystems
Kirmer, A. ; Tischew, S. ; Ozinga, W.A. ; Lampe, M. von; Baasch, A. ; Groenendael, J.M. van - \ 2008
Journal of Applied Ecology 45 (2008)5. - ISSN 0021-8901 - p. 1523 - 1530.
long-distance dispersal - seed dispersal - plant-communities - spontaneous succession - vegetation succession - restoration practice - wind dispersal - habitats - establishment - morphology
Large-scale destruction of ecosystems caused by surface mining provides an opportunity for the study of colonization processes starting with primary succession. Surprisingly, over several decades and without any restoration measures, most of these sites spontaneously developed into valuable biotope mosaics with many endangered plant species. Investigations were carried out in 10 open-cast mined sites. Data from extensive floristic mapping of mined sites and their surroundings were combined with functional traits. Using binary logistic regression, we showed that eight variables have a significant influence on the probability of the occurrence of particular plant species in mined sites. The regional species pool explained the highest proportion of variance. Further significant variables were distance of source populations, abundance in the habitat species pool, capacity for long-distance dispersal by wind and birds, terminal velocity of seeds and requirements for light and nitrogen. In the 10 study mine sites, 143 establishing events of Red List species have been recorded. For 40% of these establishing events, the nearest recorded seed source is 3-10 km away, while for 19%, the distance to the nearest seed source exceeds 10 km. This study showed for the first time that the abundance of species up to a distance of at least 17 km plays an important role in colonization processes following large-scale destruction of ecosystems. In large-scale, nutrient-deficient, open sites, an accumulation of plant species, including rare species, can be expected in time frames amenable to planning (several decades), because the sites acted as huge seed traps in the landscape. Synthesis and applications. The floristic colonization probability of restoration sites is higher if large-scale, open and nutrient-poor habitats are available. In regions where such habitats have become highly fragmented, restoration planning of derelict land (e.g. surface mines, quarries, landfills) that supports the creation of such conditions can contribute to the regional survival of rare pioneer species. In future restoration planning, a new protocol must be established that combines the utilization of site potential with spontaneous colonization processes.
Local above-ground persistence of vascular plants: life-history trade-offs and environmental constraints
Ozinga, W.A. ; Hennekens, S.M. ; Schaminée, J.H.J. ; Smits, N.A.C. ; Bekker, R.M. ; Römermann, C. ; Bakker, J.P. ; Groenendael, J.M. van - \ 2007
Journal of Vegetation Science 18 (2007)4. - ISSN 1100-9233 - p. 489 - 497.
relative growth-rate - distance seed dispersal - park grass experiment - species coexistence - extinction debt - wind dispersal - size - communities - competition - dynamics
Questions: 1. Which plant traits and habitat characteristics best explain local above-ground persistence of vascular plant species and 2. Is there a trade-off between local above-ground persistence and the ability for seed dispersal and below-ground persistence in the soil seed bank? Locations: 845 long-term permanent plots in terrestrial habitats across the Netherlands. Methods: We analysed the local above-ground persistence of vascular plants in permanent plots (monitored once a year for ca. 16 year) with respect to functional traits and habitat preferences using survival statistics (Kaplan-Meier analysis and Cox' regression). These methods account for censored data and are rarely used in vegetation ecology. Results: Local above-ground persistence is determined by both functional traits (especially the ability to form long-lived clonal connections) and habitat preferences (especially nutrient requirements). Above-ground persistence is negatively related to the ability for dispersal by wind and to the ability to accumulate a long-term persistent soil seed bank (`dispersal through time¿) and is positively related to the ability for dispersal by water. Conclusions: Most species have a half-life expectation over 15 years, which may contribute to time lags after changes in habitat quality or -configuration (`extinction debt¿). There is evidence for a trade-off relationship between local above-ground persistence and below-ground seed persistence, while the relationship with dispersal in space is vector specific. The rate of species turnover increases with productivity.
Dispersal potential in plant communities depends on environmental conditions
Ozinga, W.A. ; Bekker, R.M. ; Schaminée, J.H.J. ; Groenendael, J.M. van - \ 2004
Journal of Ecology 92 (2004)5. - ISSN 0022-0477 - p. 767 - 777.
long-distance dispersal - seed dispersal - wind dispersal - indicator values - population-size - life-history - grassland - ecology - mass - coexistence
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.