Treesearch

Constitutive chemical defenses, always expressed in the plants, and plastic defensive responses, those mobilized in response to plant injury or other cues or herbivory risk, differ in their benefits in terms of fitness for long-lived plants. Induced defenses are considered to be less expensive than constitutive preformed defenses since the cost is realized only when required. Plant defense theory predicts that, as secondary metabolism is costly for the plant, presenting effective levels of constitutive defenses and the ability of expressing efficient inducible defenses by a plant are two...

In North America, hemlock woolly adelgid (HWA; Adelges tsugae) is an exotic insect pest from Asia that is causing rapid decline of native eastern hemlock (Tsuga canadensis (L.) Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) populations. The exact physiological mechanisms that cause tree decline and mortality are not known, despite substantial research efforts on ecological impacts and potential control measures of HWA. Eastern and Carolina hemlock may be reacting to infestation in a manner similar to the response of Fraser fir (Abies fraseri (Pursh.) Poir.) to infestation by...

The elm breeding program carried out in Italy at the Institute of Plant Protection - Consiglio Nazionale delle Ricercje (CNR) during the last 40 years aimed to develop Dutch elm disease (DED)-resistant elm selections specific to the Mediterranean environment. The need for genotypes adapted to Mediterranean conditions was evident from the poor performance of the Dutch elm clones in the hot and dry areas of central Italy, and the opportunity to breed better adapted hybrids was offered by the favorable adaptation in Italy of the Siberian elm (Ulmus pumila L.), a species that does not thrive...

Routine selection is simply defined as “the ecological constraints experienced by an endemic organism that favor a relatively stable but fluctuating population structure over time.” Its antithesis is episodic selection, defined as “any sudden ecological disturbance likely to lead to a significant alteration in a species’ population structure” (Brasier 1986, 1995). In plant pathogens, examples of episodic selection are common in the context of modern anthropogenically driven disturbance conditions such as sudden exposure to crop monoculture or to a new fungicide, host, or vector; or sudden...

Emerald ash borer (EAB) (Agrilus planipennis), an introduced wood-boring insect, has killed millions of ash (Fraxinus spp.) trees in the Midwest region of the United States and Canada. However, in some areas where EAB has caused almost complete mortality of mature ash trees, a small number of healthy ash trees intermingled with the dead ash trees have been discovered, sparking interest in these “lingering” ash trees. Here we present the results of surveys in 2010 and 2011 of two populations of surviving ash trees in southeast Michigan and northwest Ohio, where the vast majority of ash...

In the eastern United States, land-use and climate change have likely contributed to declines in the abundance of Neotropical migrant birds that occupy forest interiors, but the mechanisms are not well understood. We conducted a nest-predation experiment in southern Appalachian Mountain forests (North Carolina, U.S.A.) during the 2009 and 2010 breeding seasons to determine the effects of exurban development and temperature on predator presence and the average number of days until eggs in an artificial nest were disturbed by predators. We baited artificial nests with quail (Excalfactoria...

Plant ecologists have debated the mechanisms used by plants to cope with the impact of herbivore damage for more than a century. During that time, plant resistance mechanisms, which reduce the amount of herbivore damage before and during herbivory, have received most of the attention, while plant tolerance mechanisms, which may minimize the impacts of damage after herbivory, have been less studied. The aim of this presentation is to bring the topic of plant compensatory responses, especially compensatory growth, to the front of research in plant ecology and plant-herbivore interactions. We...

Since the early 1980s, an epidemic forest disease, Japanese Oak Wilt (JOW), has been spreading from coastal areas along the Sea of Japan to the interior of Honshu island and has been devastating huge areas of forests by killing an enormous number of oak trees in urban fringe mountains, gardens, and parks. The disease is caused by a fungus, Raffaelea quercivora, and is spread by the vector beetle, Platypus quercivorus (Coleoptera: Platypodidae). On the thorax of female P. quercivorus, are several holes, so called mycangia, where several species of yeasts are kept as the beetles’ food....

The terms "resistance" and "tolerance" have been used by different scientists to refer to different things, and they have often been measured (and thus operationally defined) in ways that confuse the two concepts with each other. In keeping with the emerging consensus on resistance and tolerance, the following conceptual distinction is useful: resistance refers to traits that prevent infection or limit its extent, and tolerance refers to traits that do not reduce or eliminate infection, but instead reduce or offset its fitness consequences. Thus, resistance and tolerance can both improve...

Natural plant-pathogen associations are complex interactions in which the interplay of environment, host, and pathogen factors results in spatially heterogeneous ecological and epidemiological dynamics. The evolutionary patterns that result from the interaction of these factors are still relatively poorly understood. Recently, integration of the appropriate spatial and temporal context of the metapopulation has permitted an essential conceptual advance stressing the importance of these factors in evolutionary interactions. Yet, a major aspect of host and pathogen biologies that still needs...