Armenteras, D., Sebastian Barreto, J., Tabor, K., Molowny-Horas, R., Retana, J. (2017) Changing patterns of fire occurrence in proximity to forest edges, roads and rivers between NW Amazonian countries. Biogeosciences. 14: 2755-2765.EnllaçDoi: 10.5194/bg-14-2755-2017
Arnan X., Molowny-Horas R., Rodrigo A., Retana J. (2012) Uncoupling the effects of seed predation and seed dispersal by granivorous ants on plant population dynamics. PLoS ONE. 7: 0-0.EnllaçDoi: 10.1371/journal.pone.0042869
Secondary seed dispersal is an important plant-animal interaction, which is central to understanding plant population and community dynamics. Very little information is still available on the effects of dispersal on plant demography and, particularly, for ant-seed dispersal interactions. As many other interactions, seed dispersal by animals involves costs (seed predation) and benefits (seed dispersal), the balance of which determines the outcome of the interaction. Separate quantification of each of them is essential in order to understand the effects of this interaction. To address this issue, we have successfully separated and analyzed the costs and benefits of seed dispersal by seed-harvesting ants on the plant population dynamics of three shrub species with different traits. To that aim a stochastic, spatially-explicit individually-based simulation model has been implemented based on actual data sets. The results from our simulation model agree with theoretical models of plant response dependent on seed dispersal, for one plant species, and ant-mediated seed predation, for another one. In these cases, model predictions were close to the observed values at field. Nonetheless, these ecological processes did not affect in anyway a third species, for which the model predictions were far from the observed values. This indicates that the balance between costs and benefits associated to secondary seed dispersal is clearly related to specific traits. This study is one of the first works that analyze tradeoffs of secondary seed dispersal on plant population dynamics, by disentangling the effects of related costs and benefits. We suggest analyzing the effects of interactions on population dynamics as opposed to merely analyzing the partners and their interaction strength. © 2012 Arnan et al.
Rodríguez N., Armenteras D., Molowny-Horas R., Retana J. (2012) Patterns and trends of forest loss in the Colombian Guyana. Biotropica. 44: 123-132.EnllaçDoi: 10.1111/j.1744-7429.2011.00770.x
Spatial patterns of tropical deforestation and fragmentation are conditional upon human settlement characteristics. We analyze four different human occupation models (indigenous, colonist frontier, transition and established settlement) in the Colombian Guyana Shield at three different times: 1985, 1992 and 2002, and compared them for: (1) deforestation rates; (2) the amount of forest as classified according to a fragmentation pattern (interior forest, edge forest, perforated forest and forest patch); (3) various fragmentation metrics using repeated measures analysis of variance; and (4) potential future deforestation trends though the implementation of a spatially explicit simulation model. The indigenous and colonist frontier occupation models had low rates of deforestation (0.04%/yr), while the well-established settlement occupation model had the highest rate (3.68%/yr). Our results indicate that the four occupation models generate three deforestation patterns: diffuse, which can be subdivided into two subpatterns (indigenous and colonist), geometric (transition) and patchy (established settlement). The area with the established settlement model was highly fragmented, while in the transition occupation area, forest loss was gradual and linked to economic activities associated with the expansion of the agricultural frontier. The simulation of future trends revealed that indigenous and colonist areas had a constant, albeit small, loss of forest covers. The other models had a deforestation probability of 0.8 or more. Overall, our results highlight the need for new and urgent policies for reducing forest conversion that consider intraregional variability in human occupation linked to differences in land-use patterns. © 2011 The Author(s) Journal compilation © 2011 Association for Tropical Biology and Conservation.
Armenteras-Pascual D., Retana-Alumbreros J., Molowny-Horas R., Roman-Cuesta R.M., Gonzalez-Alonso F., Morales-Rivas M. (2011) Characterising fire spatial pattern interactions with climate and vegetation in Colombia. Agricultural and Forest Meteorology. 151: 279-289.EnllaçDoi: 10.1016/j.agrformet.2010.11.002
Vegetation burning in tropical countries is a threat to the environment, causing not only local ecological, economic and social impacts, but also large-scale implications for global change. The burning is usually a result of interacting factors, such as climate, land-use and vegetation type. Satellite-derived monthly time series datasets of rainfall, burned area and active fire detections between December 2000 and 2009 were used in this study. A map of vegetation types was also used to determine these factors' spatial and temporal variability and interactions with the total amount of burned area and active fires detected in Colombia. Grasslands represented the vegetation most affected by fires every year in terms of burned area (standardised by their total area), followed by secondary vegetation, pasture and forests. Grasslands were also most affected by active fires, but followed closely by pasture, agricultural areas, secondary vegetation and forests. The results indicated strong climate and fire seasonality and marked regional difference, partly explained by climatic differences amongst regions and vegetation types, especially in the Orinoco and Caribbean regions. The incidence of fire in the Amazon and Andes was less influenced by climate in terms of burned area impacted, but the strength of the ENSO phenomenon affected the Orinoco and the Andes more in terms of burned area. Many of the active fires detected occurred in areas of transition between the submontane and lowland Andes and the Amazon, where extensive conversion to pasture is occurring. The possible high impact of small fires on the tropical rainforest present in this transition area and the Amazonian rainforest deserves more attention in Colombia due to its previous lack of attention to its contribution to global change. © 2010 Elsevier B.V.
Rodríguez N, Armenteras D, Molowny-Horas R, Retana J (2011) Patterns and trends of forest loss in the Colombian Guyana. Biotropica doi: 10.1111/j.1744-7429.2011.00770.x.
Arnan X., Rodrigo A., Molowny-Horas R., Retana J. (2010) Ant-mediated expansion of an obligate seeder species during the first years after fire. Plant Biology. 12: 842-852.EnllaçDoi: 10.1111/j.1438-8677.2009.00294.x
Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade-intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate-seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant-mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population. © 2009 German Botanical Society and The Royal Botanical Society of the Netherlands.
Espelta J.M., Cortés P., Molowny-Horas R., Retana J. (2009) Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks. Oecologia. 161: 559-568.EnllaçDoi: 10.1007/s00442-009-1394-x
The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. © Springer-Verlag 2009.
Espelta JM, Gracia M, Molowny R, Ordoñez JL, Retana J, Vayreda J et al (2009) Els alzinars Manuals de gestió d’hàbitats. Diputació de Barcelona. Barcelona. 181 pp.
Espelta J.M., Cortés P., Molowny-Horas R., Sánchez-Humanes B., Retana J. (2008) Masting mediated by summer drought reduces acorn predation in mediterranean oak forests. Ecology. 89: 805-817.EnllaçDoi: 10.1890/07-0217.1
Temporally variable production of seed crops by perennial plants (masting) has been hypothesized to be a valuable mechanism in the reduction of seed predation by satiating and starving seed consumers. To achieve these benefits, coexisting species subjected to the same predator would benefit from a similar pattern of seeding fluctuation over time that could lead to a reduction in predation at the within-species level. We tested for the existence of an environmental factor enforcing synchrony in acorn production in two sympatric Mediterranean oaks (Quercus ilex and Q. humilis) and the consequences on within-species and between-species acorn predation, by monitoring 15 mixed forests (450 trees) over seven years. Acorn production in Q. ilex and Q. humilis was highly variable among years, with high population variability (CVp) values. The two species exhibited a very different pattern across years in their initial acorn crop size (sum of aborted, depredated, and sound acorns). Nevertheless, interannual differences in summer water stress modified the likelihood of abortion during acorn ripening and enforced within- and, particularly, between-species synchrony and population variability in acorn production. The increase in CVp from initial to mature acorn crop (after summer) accounted for 33% in Q. ilex, 59% in Q. humilis, and 60% in the two species together. Mean yearly acorn pre-dispersal predation by invertebrates was considerably higher in Q. humilis than in Q. ilex. Satiation and starvation of predators was recorded for the two oaks, and this effect was increased by the year-to-year variability in the size of the acorn crop of the two species combined. Moreover, at a longer time scale (over seven years), we observed a significant reduction in the mean proportion of acorns depredated for each oak and the variability in both species' acorn production combined. Therefore, our results demonstrate that similar patterns of seeding fluctuation over time in coexisting species mediated by an environmental cue (summer drought) may contribute to the reduction of the impact of seed predation at a within-species level. Future research should be aimed at addressing whether this process could be a factor assisting in the coexistence of Q. ilex and Q. humilis. © 2008 by the Ecological Society of America.
Ordóñez J.L., Molowny-Horas R., Retana J. (2006) A model of the recruitment of Pinus nigra from unburned edges after large wildfires. Ecological Modelling. 197: 405-417.EnllaçDoi: 10.1016/j.ecolmodel.2006.03.027
We have developed a simulation model for predicting the recruitment response of Pinus nigra from unburned edges in areas affected by large wildfires, where the regeneration of burned forests of this tree species is very low. We have simulated the distribution of P. nigra seedlings at different distances from the unburned edges by integrating empirical field data for the different processes affecting seed and seedling success. The simulation model determines the final number of seedlings established in any subplot, within the burned area, as the multiplication of a number of statistically independent processes, from cone and seed production and predation, to seed germination and seedling establishment. Probabilities are drawn at random at each time step from the experimental distributions that describe those processes. The model runs for a given number of years, thus simulating the accumulative effects on the total number of established seedlings of the different processes involved. That represents one model run, which is then repeated a sufficient number of times to calculate simulated distributions of established seedlings as a function of distance from the forest edge. The validation of those results with data from field measurements of seedling establishment in old-burned areas has demonstrated the ability of the simulation algorithm to reproduce observed results. Furthermore, the simulations carried out with the model for actual plots, located near the margins of the burned areas affected by the largest fires affecting P. nigra forests in Catalonia in recent years, have all shown striking similarities. The simulated values of established seedlings follow a Gaussian-like distribution in the first 100 m, with a wide range of 2000-25,000 seedlings/ha. There is also a clear trend for plots with medium and large trees to show an increment in increasing seedling establishment with tree density, whereas plots dominated by small trees give very low regeneration values. © 2006 Elsevier B.V. All rights reserved.
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