Invasional conflict: Do invasive insect herbivores mediate the effects of enemy release for their invasive plant hosts?

Although many factors have been proposed that potentially contribute to invasion success in plants, it remains unclear why some species successfully establish and become dominant while others do not. The most often cited explanation for the success of invasive plants worldwide is the enemy release hypothesis (ERH), which maintains that populations are kept in check by their co-evolved natural enemies in their native range, but are released from this regulation in the new range. Although there is evidence that introduced plant species often experience a decrease in damage by herbivores in the novel range, it is uncertain if this decrease affects plant productivity. The purpose of this study was 1) to determine if the invasive plant _Eugenia uniflora_ (Myrtaceae) experiences release from enemies and 2) if enemy release increases growth and survival for this species relative to co-occurring native congeners _E. axillaris_ and _E. foetida_. An insect herbivore exclusion experiment using insecticide was conducted in the field to assess differences in insect herbivore damage, leaf number, height, and survival for all three species. The results contradict the ERH, showing that _E. uniflora_ has a greater proportion of damaged leaves and experiences a greater reduction in this damage when herbivores are excluded from the system, relative to the two native congeners. A trend exhibited by the data also demonstrates that exclusion of enemies positively affects growth and survival for all three species, indicating that _E. uniflora_ has not experienced enemy release in its new range. This may be explained by the fact that _E. uniflora_ exhibits, with few exceptions, mostly damage characteristic of a notching weevil, _Myllocerus undatus_, a recent import from Sri Lanka. _E. uniflora_ originates in Brazil, so these species share no coevolutionary history. The results of this study indicate that _M. undatus_ may have a negative effect on _E. uniflora_, potentially benefitting the native species by reducing competition. In contrast to invasional meltdown, this is a potential example of another type of interaction, which we have termed “invasional conflict”. This interaction will undoubtedly become much more prevalent as more species are introduced, become established, and interact with one another, forming new biological associations. 
&#xa

Direct and Legacy Effects of Long-Term Elevated CO2 on Fine Root Growth and Plant-Insect Interactions

Increasing atmospheric CO2 concentrations alter leaf physiology, with effects that cascade to communities and ecosystems. Yet, responses over cycles of disturbance and recovery are not well known, because most experiments span limited ecological time. We examined the effects of CO2 on root growth, herbivory and arthropod biodiversity in a woodland from 1996 to 2006, and the legacy of CO2 enrichment on these processes during the year after the CO2 treatment ceased. We used minirhizotrons to study root growth, leaf censuses to study herbivory and pitfall traps to determine the effects of elevated CO2 on arthropod biodiversity. Elevated CO2 increased fine root biomass, but decreased foliar nitrogen and herbivory on all plant species. Insect biodiversity was unchanged in elevated CO2. Legacy effects of elevated CO2 disappeared quickly as fine root growth, foliar nitrogen and herbivory levels recovered in the next growing season following the cessation of elevated CO2. Although the effects of elevated CO2 cascade through plants to herbivores, they do not reach other trophic levels, and biodiversity remains unchanged. The legacy of 10yr of elevated CO2 on plant-herbivore interactions in this system appear to be minimal, indicating that the effects of elevated CO2 may not accumulate over cycles of disturbance and recovery

Identifying predictors of translocation success in rare plant species

The fundamental goal of a rare plant translocation is to create self-sustaining populations with the evolutionary resilience to persist in the long term. Yet, most plant translocation syntheses focus on a few factors influencing short-term benchmarks of success (e.g., survival and reproduction). Short-term benchmarks can be misleading when trying to infer future growth and viability because the factors that promote establishment may differ from those required for long-term persistence. We assembled a large (n = 275) and broadly representative data set of well-documented and monitored (7.9 years on average) at-risk plant translocations to identify the most important site attributes, management techniques, and species' traits for six life-cycle benchmarks and population metrics of translocation success. We used the random forest algorithm to quantify the relative importance of 29 predictor variables for each metric of success. Drivers of translocation outcomes varied across time frames and success metrics. Management techniques had the greatest relative influence on the attainment of life-cycle benchmarks and short-term population trends, whereas site attributes and species' traits were more important for population persistence and long-term trends. Specifically, large founder sizes increased the potential for reproduction and recruitment into the next generation, whereas declining habitat quality and the outplanting of species with low seed production led to increased extinction risks and a reduction in potential reproductive output in the long-term, respectively. We also detected novel interactions between some of the most important drivers, such as an increased probability of next-generation recruitment in species with greater seed production rates, but only when coupled with large founder sizes. Because most significant barriers to plant translocation success can be overcome by improving techniques or resolving site-level issues through early intervention and management, we suggest that by combining long-term monitoring with adaptive management, translocation programs can enhance the prospects of achieving long-term success

Gringos in the tropic : a study of Americans in Mexico

In this paper, I will discuss the history of American migrants in Mexico, the Americans that are currently residing in Mexico (with an especial emphasis on retirees), and in general, the way that this is part of a more globally connected world. The migration of skilled professionals who leave a country out of free choice is not as commonly discussed

Ecology Global Insights & Investigations

xxi, 579 hlm.; 27,5 c