Masting plants: Why combine abstinence and lust in reproduction?

La majoria de plantes perennes produeixen llavors cada any, però n’hi ha algunes que mostren un comportament reproductiu estrany: les seves poblacions produeixen extraordinàries collites de manera erràtica i sincrònica, però passen alguns anys pràcticament sense reproduir-se. Són les espècies anyívoles i el motiu d’aquest comportament sexual, com es produeix, i les conseqüències que té per a les xarxes tròfiques ha intrigat els ecòlegs. En aquest treball presentem un resum del coneixement actual sobre les causes evolutives i ecològiques que promourien aquest comportament. Les dues hipòtesis més versemblants de la seva evolució serien els avantatges de controlar les poblacions de depredadors de llavors i afavorir que algunes escapin (saciat dels depredadors) i/o una millor eficàcia en la pol·linització de plantes pol·linitzades pel vent (eficiència en la pol·linització). La variabilitat entre anys en la mida de les collites seria el resultat de la possibilitat que les plantes puguin dedicar més o menys recursos a la reproducció a partir de les condicions ambientals (p. ex. meteorològiques, de mobilització de nutrients) mentre que la sincronia entre individus, fins i tot a grans escales espacials, seria el resultat de l’anomenat Efecte Moran, és a dir, la resposta a una condició ambiental amb àmplia sincronia espacial com és la meteorologia i els seus efectes en la floració o la maduració dels fruits. Finalment, es presenta el coneixement més recent sobre les causes que determinen que una espècie com l’alzina (Quercus ilex), tan important i abundant al nostre país, sigui anyívola i les seves conseqüències.Most perennial plants produce seeds every year, but some species show a bizarre reproductive behaviour: they produce bumper crops randomly and synchronously in some years, while in other years they produce virtually no seeds. These are known as masting species and the benefits of this behaviour, how it occurs, and the consequences for trophic networks have long intrigued ecologists. Here we present a summary of current knowledge about the evolutionary and ecological causes that promote masting. The two most likely hypotheses for its evolution are the advantages of controlling seed predator populations and encouraging some seeds to escape (predator satiation) and/or better efficiency in the pollination of wind-pollinated plants (pollination efficiency). The variability between years in the size of crops results from the fact that plants devote more or fewer resources to reproduction depending on the environmental conditions (e.g. meteorological conditions and nutrient mobilization). In addition, the synchrony between individuals, even at large spatial scales, is the result of the so-called Moran Effect: i.e. the response to an environmental condition with a broad spatial synchronization such as meteorology and its effects on the flowering or maturation of the fruits. Finally, we present the most recent knowledge on the reasons why the holm oak (Quercus ilex), so important and abundant in Catalonia, exhibits masting behaviour, and its consequences

Herbivory on the pedunculate oak along an urbanization gradient in Europe : Effects of impervious surface, local tree cover, and insect feeding guild

Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that-just like in non-urban areas-plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.Peer reviewe

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

International audienceThe relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential

Data from: Effects of nitrogen deposition on reproduction in a masting tree: benefits of higher seed production are trumped by negative biotic interactions

Relatively little is known about the effects of anthropogenic environmental changes on reproductive ecology of trees. Yet, recruitment is a primary determinant of the long-term dynamics of plant populations in changing environments. We used the Long-Term Ecological Research site at Harvard Forest to evaluate the effects of chronic (over 25 years) nitrogen fertilization on reproductive ecology of red oaks (Quercus rubra). Oaks growing in fertilized plots produced 4–9 times more acorns than control trees. However, nitrogen deposition simultaneously affected oaks’ biotic interactions. It increased pre-dispersal seed predation by insects (primarily weevils, Curculio spp.) on fertilized plots, most likely as the result of the disruption of predator satiation. In addition, infestation by weevils was more likely to result in embryo destruction in fertilized than in control acorns. Furthermore, the proportion of acorns dispersed and cached by rodents decreased on fertilized plots. Finally, germination of fertilized acorns was lower than control acorns, even after controlling for the effects of weevils and rodents. Inclusion of the altered biotic interactions reversed the final picture of the effects of long-term nitrogen fertilization on oak reproduction: the positive effects on acorn quantity were trumped by the nitrogen-mediated changes in biotic interactions. Synthesis. Our results stress the importance of considering indirect effects and consumer interactions when evaluating the effects of environmental change on plant population dynamics. Long-term nitrogen fertilization has a strong potential to decrease the recruitment of masting trees. Given the ubiquitous increase in the anthropogenic nitrogen deposition, processes similar to those found in our system might operate in others, resulting in a widespread alteration in trees’ recruitment dynamics

Effectiveness of predator satiation in masting oaks is negatively affected by conspecific density

Variation in seed availability shapes plant communities, and is strongly affected by seed predation. In some plant species, temporal variation in seed production is especially high and synchronized over large areas, which is called ‘mast seeding’. One selective advantage of this phenomenon is predator satiation which posits that masting helps plants escape seed predation through starvation of predators in lean years, and satiation in mast years. However, even though seed predation can be predicted to have a strong spatial component and depend on plant densities, whether the effectiveness of predator satiation in masting plants changes according to the Janzen-Connell effect has been barely investigated. We studied, over an 8-year period, the seed production, the spatiotemporal patters of weevil seed predation, and the abundance of adult weevils in a holm oak (Quercus ilex) population that consists of trees interspersed at patches covering a continuum of conspecific density. Isolated oaks effectively satiate predators, but this is trumped by increasing conspecific plant density. Lack of predator satiation in trees growing in dense patches was caused by re-distribution of insects among plants that likely attenuated them against food shortage in lean years, and changed the type of weevil functional response from type II in isolated trees to type III in trees growing in dense patches. This study provides the first empirical evaluation of the notion that masting and predator satiation should be more important in populations that start to dominate their communities, and is consistent with the observation that masting is less frequent and less intense in diverse forests.M. B. was supported by (Polish) National Science Foundation grants no. Preludium 2015/17/N/NZ8/01565, and Etiuda no. 2015/16/T/NZ8/00018, and by the Foundation for Polish Science Start Scholarship. R. B. was funded by a contract of the Atracción de Talento Investigador Programme (Gobierno de Extremadura TA13032). This work was financed by the PII1C09-0256-9052 and PPII-2014-01-P projects of the Junta de Comunidades de Castilla-La Mancha/European Social Fund, AGL2014-54739-R from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (FEDER) and the project BEEMED (SGR913) (Generalitat de Catalunya).Peer Reviewe

rodent_dispersal

Seed tracking experiment data. plot - site identifier; station - seed station ID; seed - acorn ID; weight - acorn mass; harvest - binomial variable, acorn harvested (1) or not (0); similar with columns: removed, found, eaten, cached, surface (i.e. found on surface); distance - removal distance [cm

weevil_abund

Weevil abundance dataset (no. of weevil larvae per acorns, divided into bottom and apical part of the acorn). year - year of the data collection; treat - tree ID; treat - nitrogen treatment (con - control, ln - low N, hn - high N); weight - acorn mass; height and width - acorn dimensions; part - acorn part (bottom and top); weev - no. of weevils; prev - acorn infested (1) or not (0); prod - estimate of acorn production be the tre