Abstract
As biological invasions increasingly threaten biodiversity, the removal of invasive nonnative species emerges as a possibility to recover the structure and function of native communities. ...Yet, we have limited knowledge of how communities assemble after nonnative removals. Since most ecosystems are invaded by multiple nonnative species, the impact of their removal likely depends on the interactions among nonnative species which, in turn, are contingent on the environmental context in which they occur.
We evaluated the community assembly after the targeted removal of two highly invasive shrubs, Sweetbriar rose (
Rosa rubiginosa
) and Scotch broom (
Cytisus scoparius
). The removal was performed at two different times in the growing season (early or late removal) in field and mesocosm communities. In search of general patterns across species, we modelled species responses as a function of their origin (i.e. native/nonnative) and functional traits.
We found evidence for negative and asymmetric interactions between dominant invasive species that translated into changes in the abundances of the rest of the species in the community. Depending on the identity of the removed species, the removal of invasive species affected community assembly by promoting other nonnative species or hindering the performance of native species. These effects were modulated by the timing of removal and did not depend on leaf or seed traits.
Synthesis
. Accounting for nonnative interactions and their temporal dependency should improve our inferences about assembly processes and the effectiveness of nonnative removal aimed at reducing the accumulation of nonnatives.
Resumen
A medida que las invasiones biológicas amenazan crecientemente la biodiversidad, la remoción de especies no‐nativas surge como una posibilidad para recuperar la estructura y el funcionamiento de las comunidades nativas. Sin embargo, tenemos un conocimiento limitado sobre cómo se reensamblan las comunidades después de la remoción de especies no‐nativas. Dado que la mayoría de los ecosistemas están invadidos por múltiples especies no‐nativas, el impacto de su remoción probablemente depende de las interacciones entre las especies no‐nativas que, a su vez, dependen del contexto ambiental en el que ocurren.
Evaluamos el ensamble comunitario después de la remoción selectiva de dos arbustos altamente invasivos, rosa mosqueta (
Rosa rubiginosa
) y retama (
Cytisus scoparius
). La remoción se realizó en dos momentos de la temporada de crecimiento (remoción temprana o tardía), en comunidades de campo y mesocosmos. En busca de patrones generales entre especies, modelamos las respuestas de las especies en función de su origen (i.e. nativo/no‐nativo) y rasgos funcionales.
Encontramos evidencia de interacciones negativas y asimétricas entre las especies invasoras dominantes que se tradujeron en cambios en las abundancias del resto de las especies en la comunidad. Dependiendo de la identidad de la especie removida, la remoción de especies invasoras afectó el reensamble de la comunidad al promover otras especies no‐nativas o reducir el desempeño de las especies nativas. Estos efectos fueron modulados por el momento de remoción y no dependieron de los rasgos de las hojas o de las semillas.
Síntesis
. Considerar las interacciones no‐nativas y su dependencia temporal debería mejorar nuestras inferencias sobre los procesos de reensamble y la efectividad de la remoción de especies invasoras destinada a reducir la acumulación de especies no‐nativas.
Abstract
An ongoing restoration challenge is to recover native communities after the removal of invasive species. Because priority effects (i.e. the order and timing of species arrival) can strongly ...determine the trajectory of community assembly, their intentional manipulation is gaining attention to manage invasive plants and achieve restoration goals. Yet, ecologists and conservationists rarely consider how the order and timing of species removal—
inverse priority effect
—may impact future plant communities.
Here, we evaluated the dependence of community reassembly on inverse priority effects by experimentally removing the target invasives Sweetbriar rose (
Rosa rubiginosa
) and Scotch broom (
Cytisus scoparius
) in field and mesocosm communities. We manipulated removal order (rose before broom vs. broom before rose) and timing (simultaneously early vs. simultaneously late in the season). We performed a hierarchical modeling of species sommunity to assess differences in community structure in response to order and timing of removal, and to evaluate whether species origin and leaf and seed traits were associated with species responses.
We found that the order of removal was as important as timing driving community reassembly. Simultaneous removal favoured nonnatives, more so when performed early. Sequential removals led to contrasting communities. Rose before broom removal also favoured nonnative grasses at expense of native species, whereas the inverse order produced small changes in communities. In general, species with high specific leaf area were boosted, regardless of their seed size.
Synthesis and applications
. Inverse priority effects are neglected mechanisms that can drive variability in the reassembly of plant communities and can potentially upgrade invasive species management. These historical contingencies suggest the existence of an optimal order of removal that facilitates the recovery of the native community. We found that simultaneous removal promoted secondary invasions to a greater extent than sequential removals. Furthermore, removal order affected post‐removal community structure. In our system, we suggest removing the rose before the broom to hinder nonnatives and pave the way for restoration of native communities. Our results show that manipulation of the order and timing of removal can help to achieve restoration goals.
Resumen
La recuperación de las comunidades nativas luego de la remoción de especies invasoras es un desafío para la restauración ecológica. Dado que los efectos de prioridad (i.e., el orden y el tiempo de llegada de las especies) pueden determinar fuertemente la trayectoria de ensamble de la comunidad, su manipulación intencional está ganando atención para manejar plantas invasoras y lograr objetivos de restauración. Sin embargo, los ecólogos y conservacionistas raramente consideran cómo el orden y el tiempo de remoción de especies—
efecto de prioridad inverso
—pueden afectar a las futuras comunidades de plantas.
En este estudio, evaluamos la dependencia del re‐ensamble comunitario a los efectos de prioridad inversos mediante la remoción experimental de dos plantas invasoras focales: la rosa mosqueta (
Rosa rubiginosa
) y la retama (
Cytisus scoparius
) en comunidades de campo y mesocosmos. Manipulamos el orden de remoción (rosa antes de retama vs. retama antes de rosa) y el tiempo (simultáneamente temprano vs. tarde en la temporada). Realizamos un modelo jerárquico de comunidad de especies para evaluar las diferencias en la estructura comunitaria en respuesta al orden y tiempo de remoción, y para determinar si el origen de las especies y los rasgos de sus hojas y semillas modulan las respuestas de las especies.
Encontramos que tanto el orden como el tiempo de remoción influenciaron el re‐ensamble comunitario. La remoción simultánea favoreció a especies no‐nativas, especialmente cuando se realizó temprano en la temporada. Las remociones secuenciales condujeron a comunidades contrastantes. La remoción de rosa antes de retama favoreció a gramíneas no‐nativas en detrimento de las especies nativas, mientras que el orden inverso produjo cambios pequeños en las comunidades. En general, las especies con una superficie foliar específica alta fueron favorecidas, independientemente del tamaño de su semilla.
Síntesis y aplicaciones.
Los efectos de prioridad inversos son mecanismos raramente estudiados que pueden generar variabilidad en el re‐ensamble de las comunidades de plantas y potencialmente mejorar el manejo de especies invasoras. Estas contingencias históricas sugieren la existencia de un orden óptimo de remoción que facilitaría la recuperación de la comunidad nativa. Encontramos que las remociones simultáneas promovieron invasiones secundarias en mayor medida que las remociones secuenciales. Además, el orden de remoción afectó la estructura comunitaria luego de la remoción. En nuestro sistema, sugerimos que la remoción de la rosa antes que la retama puede desfavorecer a especies no‐nativas y allanar el camino para la restauración de las comunidades nativas. Así, nuestros resultados muestran que la manipulación del orden y tiempo de remoción puede ayudar a lograr los objetivos de restauración.
Areas used for livestock production and dominated by native grasses represent a unique opportunity to reconcile biodiversity conservation and livestock production. However, limited knowledge of ...individual species’ responses to rangeland management restricts our capacity to design grazing practices that favor endangered species and other priority birds. In this work, we applied Hierarchical Modelling of Species Communities (HMSC) to study individual species responses, as well as the influence of traits on such responses, to variables related to rangeland management using birds of the Rio de la Plata Grasslands as a case study. Based on presence–absence data collected in 454 paddocks across 46 ranches we inferred the response of 69 species considering imperfect detection. This degree of detail fills a major gap in rangeland management, as species‐level responses can be used to achieve targeted conservation goals other than maximizing richness or abundance. We found that artificial pastures had an overall negative impact on many bird species, whereas the presence of tussocks had a positive effect, including all threatened species. Grassland specialists were in general sensitive to grass height and tended to respond positively to tussocks but negatively to tree cover. Controlling grass height via adjustments in stocking rate can be a useful tool to favor grassland specialists. To favor a wide range of bird species in ranches, a mosaic of short and tall native grasslands with patches of tussocks and trees is desirable. We also found that species‐specific responses were modulated by their traits: small‐sized birds responded positively to tussocks and tree cover while large species responded negatively to increasing grass height. Ground foragers preferred short grass while birds that scarcely use this stratum were not affected by grass height. Results on the influence of traits on bird responses are an important novelty in relation to previous work in rangelands and potentially increase our predicting capacity and model transferability across grassland regions.
Network metrics are widely used to infer the roles of mutualistic animals in plant communities and to predict the effect of species' loss. However, their empirical validation is scarce. Here we ...parameterized a joint species model of frugivory and seed dispersal with bird movement and foraging data from tropical and temperate communities. With this model, we investigate the effect of frugivore loss on seed rain, and compare our predictions to those of standard coextinction models and network metrics. Topological coextinction models underestimated species loss after the removal of highly linked frugivores with unique foraging behaviours. Network metrics informed about changes in seed rain quantity after frugivore loss. However, changes in seed rain composition were only predicted by partner diversity. Nestedness, closeness, and d’ specialisation could not anticipate the effects of rearrangements in plant–frugivore communities following species loss. Accounting for behavioural differences among mutualists is critical to improve predictions from network models.
In this work we test if frequently used network metrics can predict the vulnerability of plant communities to extinctions and detect frugivores of disproportionate importance. For this, we simulated scenarios of frugivores’ loss in a model able to predict frugivory in six communities. Unlike network metrics, in our model pairwise interactions emerged from frugivores’ foraging and movement decisions. Network metrics informed about quantitative changes in the seed rain but frequently failed to predict composition outcomes. This was partly because they could not anticipate rewiring dynamics after frugivores' loss. Thus, incorporating animal behavior will be critical in the development and performance of the new generation of network metrics.
The behavioural complementarity of fruit‐eating animals is thought to exert a key role in plant community assembly. However, a mechanistic understanding of the causal links between the two processes ...is still lacking.
This study assesses whether complementarity between dispersers in feeding and microhabitat‐use behaviour enhances community‐scale dispersal services, resulting in a more diverse community of seedlings.
We used a Bayesian approach to connect a comprehensive database of seed dispersal effectiveness at a community scale with a transition probability model that accounts for behavioural complementarity. Our model system was the thermosclerophyllous shrubland of the Canary Islands. There, fleshy‐fruited plants rely on two types of frugivores: lizards and birds.
Lizards consumed all plant species and preferentially used open areas, whereas birds foraged for small single‐seeded fruits and dispersed their seeds beneath plants. Through feeding on different sets of plants, they generated a rich seed‐rain community. By diversifying the microhabitat of deposition, more species could find suitable recruitment sites.
Distinct foraging and microhabitat‐use choices led to complementary dispersal services. Lizards ensured that all plant species were present in the seedling community, while birds promoted a more even distribution of them. As a result, diversity in the community of seedlings was enhanced.
Overall, our work underscores that behavioural complementarity promotes diversity in the early‐regenerating plant communities. These enhanced dispersal services rely on the presence of all functional groups. Thus, in communities where frugivores display unique behaviours, preserving a diverse community of dispersers should be a conservation target.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
We used an agent‐based model to test the hypothesis that diet complementation by frugivores can promote the persistence of rare plant species in communities (DCH).
Models simulated bird movement, ...frugivory, seed dispersal and plant recruitment on landscapes that differed in their degree of fragmentation and in their degree of fruiting species mixing at the scale of frugivores’ foraging decisions.
Diet complementation promoted the dispersal of rare species without the need of a priori preference from birds. The effects of landscape structure on the dispersal of rare plants were small (<5%) compared to positive effects of diet complementation because birds tracked the nutrients contained in rare fruits to balance their diets. However, resource‐tracking of rare fruits increased foraging costs up to 20% of net energy intakes.
During postdispersal stages, density‐dependent mortality only conferred advantages to rare plants when located within heterospecific plant patches. Still, thanks to rare‐biased dispersal, rare plants showed the highest seed dispersal effectiveness irrespectively of landscape configuration.
Our theoretical approach presents a behavioural mechanism by which fruit choice can act as a frequency‐dependent mechanism conferring rare species advantages as important as classic postdispersal density‐dependent processes.
We hope that this study stimulates future work aimed at evaluating the importance of diet complementation in structuring the composition and spatial patterning of plant communities.
A plain language summary is available for this article.
Plain Language Summary
Generalist mice are key species for the long-term dynamics of fragmented forests due to their dual role as seed dispersers or predators of the dominant trees. Wood mice, Apodemus sylvaticus, usually ...act as a net predator in woodlots due to higher winter densities and earlier winter reproduction than in forests. Here we analyze the recruitment expectations of young mice born in woodlots in relation to food availability through an index of developmental stability that combined values of fluctuating asymmetry (FA) for six traits of the lower mandibles. FA was measured in young and adult mice caught at the end of the winter in control woodlots, food-supplemented woodlots and in a nearby large forest. Despite low sample sizes (n = 9 for young and n = 74 for adults), FA in young mice born in control woodlots were significantly higher than in those from food-supplemented woodlots and the forest and in all adults. Food limitation in woodlots was thus associated with increased developmental instability of young mice, but it had no effect on adults. Instability likely reduced the survival prospects of young mice through increased mortality, and this should be compensated by yearly recolonization of woodlots by adults from the agricultural matrix in autumn and winter. Future work analyzing mechanisms suggested here but using non-lethal methods will be important to clarify the impacts of FA on the population dynamics of wood mice.
Land‐use changes are expected to affect plant–disperser conditional mutualisms through changes in animal behavior. We analyzed the oak–rodent conditional mutualism in Mediterranean fragmented forests ...at two climatically different locations. We quantified fragmentation effects on seed dispersal effectiveness and assessed if such effects were due to changes in habitat structure and intraspecific competition for acorns in fragmented areas. Fragmentation decreased cover from predators within mouse territories as well as intraspecific competition for acorns. This resulted in lower dispersal effectiveness in small forest fragments. Globally, habitat structure was the main driver in mouse foraging decisions. In small fragments, low shelter availability precluded mouse movements, leading to short mobilization distances and low caching rates. However, as the proportion of cover from predators increased, mice were able to modulate their foraging decisions depending on intraspecific competition for acorns, resulting in higher dispersal quality. In addition to fragmentation effects, delayed breeding in the southern locality caused lower number of rodents during the dispersal season, which reduced acorn mobilization rates. Our study shows that seed dispersal patterns in managed systems can be analyzed as the result of management effects on key environmental factors in dispersers’ foraging decisions.
To address whether preoperative chemotherapy plus surgery or surgery plus adjuvant chemotherapy prolongs disease-free survival compared with surgery alone among patients with resectable ...non-small-cell lung cancer.
In this phase III trial, 624 patients with stage IA (tumor size > 2 cm), IB, II, or T3N1 were randomly assigned to surgery alone (212 patients), three cycles of preoperative paclitaxel-carboplatin followed by surgery (201 patients), or surgery followed by three cycles of adjuvant paclitaxel-carboplatin (211 patients). The primary end point was disease-free survival.
In the preoperative arm, 97% of patients started the planned chemotherapy, and radiologic response rate was 53.3%. In the adjuvant arm, 66.2% started the planned chemotherapy. Ninety-four percent of patients underwent surgery; surgical procedures and postoperative mortality were similar across the three arms. Patients in the preoperative arm had a nonsignificant trend toward longer disease-free survival than those assigned to surgery alone (5-year disease-free survival 38.3% v 34.1%; hazard ratio HR for progression or death, 0.92; P = .176). Five-year disease-free survival rates were 36.6% in the adjuvant arm versus 34.1% in the surgery arm (HR 0.96; P = .74).
In early-stage patients, no statistically significant differences in disease-free survival were found with the addition of preoperative or adjuvant chemotherapy to surgery. In this trial, in which the treatment decision was made before surgery, more patients were able to receive preoperative than adjuvant treatment.
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