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All individuals transition through various life stages over the course of their development and nearly all organisms must contend with infectious disease at some point in their lives. Yet the intersection of these two universal features of life—stage structure and infectious disease—and their joint effects on population dynamics are poorly understood. Here, we develop a two-stage population model in which density dependence acts on juvenile maturation, and infectious disease affects either juveniles or adults via reduction in maturation, reproduction, or survival. In the absence of disease, this form of density dependence can generate persistent population oscillations. We examine whether infectious disease further accentuates these oscillations (by augmenting their amplitude) or stabilizes them (by reducing their amplitude). We find that, for moderate transmission rates (a proxy for disease incidence), disease can stabilize dynamics. In contrast, fast disease transmission is not generally stabilizing, which is, at least in part, due to disease overexploitation of the infectious class. Hydra effects are possible in the model due to density overcompensation and occur when disease increases juvenile mortality or decreases adult fecundity (but do not occur when disease augments adult mortality or reduces maturation). Slow maturation, large disease-free population size, and strong density-dependent population regulation can each lower the transmission rate required for the infectious disease to invade the population. [ABSTRACT FROM AUTHOR]

Populations subject to substantial environmental change that decreases absolute fitness (expected number of offspring per individual) to less than one must adapt to persist. The probability of adaptive evolutionary rescue may be influenced by factors intrinsic to the organism itself, or by features specific to the individual population and its environment. An important question (given the increasing prevalence of environmental change) is the predictability of evolutionary rescue. We used an individual-based simulation model and a related analytic model to examine population persistence, given a continuously changing environment that leads to a linear change in the optimum for a phenotypic trait under selection. Population persistence was not well predicted by the population genetics at the start of environmental change, which contrasts strongly with the results shown in prior work for persistence after a sudden environmental change. Larger populations, which had a greater scope for the generation and maintenance of beneficial genetic variation, showed a clear advantage, but increasing the rate of environmental change always decreased the probability of persistence. Extinctions occurred throughout the period of continuous change, and populations that went extinct showed little sign of their eventual fate until shortly before extinction. Partially clonal populations showed less predictability and greater vulnerability to extinction when impacted by continuous change than did fully sexual populations—any advantage gained by the initial transmission of well-adapted phenotypes via clonal reproduction is lost as the phenotypic optimum continues to shift and the generation of novel variation is required for continuous adaptation. [ABSTRACT FROM AUTHOR]

Exotic species are often predicted to successfully invade when their functional traits differ from species in recipient communities. Many studies have related trait differences among natives and invaders to competitive outcomes. Few studies, however, have tested whether functionally similar invaders have similar competitive impacts on natives. We investigated interactions in communities of a native annual forb Waitzia acuminata (Asteraceae) and two invasive annual grasses that are ecologically similar and co-occur in southwestern Australia. Using a combination of field and laboratory experiments and several performance measures, we assessed impacts of these grasses on W. acuminata. We also examined differences among species in their responses to intraspecific versus interspecific competition, including their frequency dependence. The two similar exotic grasses differed in interaction impacts, with one facilitating and the other suppressing the native. In general, intraspecific competition was stronger than interspecific competition for the native, while evidence of competition was weak for the exotics. These patterns may reflect that W. acuminata does well in these communities due to the combined impacts of stabilization and facilitation, whereas the exotics benefit from limited stabilization (mediated by their weak intraspecific competition) or weak interspecific competition with W. acuminata. We found divergent impacts of the exotic species despite their similar functional traits. We demonstrate that a native species may benefit from interactions with an exotic "benefactor" species, highlighting the potential importance of positive interactions in invaded communities. Our findings underscore the necessity of considering neutral and positive interactions in addition to competition in understanding invasion dynamics in real plant communities. [ABSTRACT FROM AUTHOR]

The article focuses on role of emergence and accumulation of pathogens on non-native plant invaders in promoting native species recovery. It states findings of a study indicating accumulation of pathogens and reduced performance of a widespread invader due to infectious disease, and mentions that s research published in the issue which concludes that pathogen accumulation cannot reverse the impacts of invasive plants. It notes that outcome of pathogen emergence is difficult to predict.

Current unprecedented declines in biodiversity reduce the ability of ecological communities to provide many fundamental ecosystem services. Here we evaluate evidence that reduced biodiversity affects the transmission of infectious diseases of humans, other animals and plants. In principle, loss of biodiversity could either increase or decrease disease transmission. However, mounting evidence indicates that biodiversity loss frequently increases disease transmission. In contrast, areas of naturally high biodiversity may serve as a source pool for new pathogens. Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases. [ABSTRACT FROM AUTHOR]

Fire frequency has significant effects on the biota of tallgrass prairie, including mammals, vascular plants and birds. Recent concern has been expressed that widespread annual burning, sometimes in combination with heavy livestock grazing, negatively impacts the biota of remaining prairie remnants. A common management recommendation, intended to address this problem, is to create a landscape with a mosaic of different burn regimes. Pitfall trapping was used to investigate the impacts of fire pattern on the diversity and species composition of ground beetles (Coleoptera: Carabidae) at Konza Prairie Biological Station in eastern Kansas, USA. Trapping was conducted over three seasons in landscape units burned on average every 1, 4, or 20 years, and in a fourth season across the available range of vegetative structure to assess the variability of the community within the study system. In the fifth season communities were also followed immediately after two fire events to detect within-season effects of fire and to study short-term patterns of post-disturbance community assembly. Fire frequency had comparatively minimal effects on ground beetle diversity measures, and most numerically common species were observed widely across habitat and management types. Fire frequency effects were manifested primarily in changes in abundance of common species. Colonization of burned areas apparently did not occur from juxtaposed non-burned areas, but from underground or from long distances. While these results suggest that widespread annual burning of tallgrass prairie remnants may not have dramatic effects on prairie ground beetles, we urge caution regarding the application of these results to other taxa within tallgrass prairie. [ABSTRACT FROM AUTHOR]

Predation can be intense, creating strong direct and indirect effects throughout food webs. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics. Species with complex life histories often shift habitats during their life cycles and provide potent conduits coupling ecosystems. Thus, local interactions that affect predator abundance in one ecosystem (for example a larval habitat) may have reverberating effects in another (for example an adult habitat). Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries. Fish reduce larval dragonfly abundances in ponds, leading to fewer adult dragonflies nearby. Adult dragonflies consume insect pollinators and alter their foraging behaviour. As a result, plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds. Our results confirm that strong species interactions can reverberate across ecosystems, and emphasize the importance of landscape-level processes in driving local species interactions. [ABSTRACT FROM AUTHOR]

Effects of the periodical cicada (Magicicada spp.) on forest dynamics are poorly documented. A 1998 emergence of M. cassini in eastern Kansas led to colonization of a fragmented experimental landscape undergoing secondary succession. We hypothesized that per-tree rates of oviposition damage by cicadas would reflect: (1) distance from the source of the emergence, (2) patch size, and (3) local tree density. Ovipositing females displayed clear preferences for host species and damage incidence showed predictable spatial patterns. Two species (smooth sumac, Rhus glabra, and eastern red cedar, Juniperus virginiana) were rarely attacked, whereas others (rough-leaved dogwood, Cornus drummondii; slippery elm, Ulmus rubra; box elder, Acer negundo, and honey locust, Gleditsia triacanthos) were strongly attacked. The dominant early successional tree, dogwood, received on average the most attacks. As predicted, attacks per stem declined strongly with distance from the emergence source, and with local stem density (a "dilution" effect). Contrary to expectations, there were more attacks per stem on larger patches. Because ovipositing cicadas cut damaging slits in host tree branches, potentially affecting tree growth rate, competitive ability, and capacity to reproduce, cicada damage could potentially influence spatial variation in secondary succession. [ABSTRACT FROM AUTHOR]

The article focuses on the problem of understanding the stability of complex food webs. It was emphasized that ecological communities are among the most complex entities studied by scientists, as they are composed of thousands of species with many distinct lifestyles, interacting in a myriad of ways.

Comments on research to determine the origins of ecological specialization. Possible causes of functional degeneration and habitat specialization, including mutations; Confinement of replicate, genetically homogeneous lineages of bacteria to a simple environment; Statement that results may better predict the exclusion of a particular lineage through indirect competition for resources.