Environmental regulation can arise under minimal assumptions

Models that demonstrate environmental regulation as a consequence of organism and environment coupling all require a number of core assumptions. Many previous models, such as Daisyworld, require that certain environment-altering traits have a selective advantage when those traits also contribute towards global regulation. We present a model that results in the regulation of a global environmental resource through niche construction without employing this and other common assumptions. There is no predetermined environmental optimum towards which regulation should proceed assumed or coded into the model. Nevertheless, polymorphic stable states that resist perturbation emerge from the simulated co-evolution of organisms and environment. In any single simulation a series of different stable states are realised, punctuated by rapid transitions. Regulation is achieved through two main subpopulations that are adapted to slightly different resource values, which force the environmental resource in opposing directions. This maintains the resource within a comparatively narrow band over a wide range of external perturbations. Population driven oscillations in the resource appear to be instrumental in protecting the regulation against mutations that would otherwise destroy it. Sensitivity analysis shows that the regulation is robust to mutation and to a wide range of parameter settings. Given the minimal assumptions employed, the results could reveal a mechanism capable of environmental regulation through the by-products of organisms.     

Linking nitrogen partitioning and species abundance to invasion resistance in the Great Basin

Resource partitioning has been suggested as an important mechanism of invasion resistance. The relative importance of resource partitioning for invasion resistance, however, may depend on how species abundance is distributed in the plant community. This study had two objectives. First, we quantified the degree to which one resource, nitrogen (N), is partitioned by time, depth and chemical form among coexisting species from different functional groups by injecting ¹⁵N into soils around the study species three times during the growing season, at two soil depths and as two chemical forms. A watering treatment also was applied to evaluate the impact of soil water content on N partitioning. Second, we examined the degree to which native functional groups contributed to invasion resistance by seeding a non-native annual grass into plots where bunchgrasses, perennial forbs or annual forbs had been removed. Bunchgrasses and forbs differed in timing, depth and chemical form of N capture, and these patterns of N partitioning were not affected by soil water content. However, when we incorporated abundance (biomass) with these relative measures of N capture to determine N sequestration by the community there was no evidence suggesting that functional groups partitioned different soil N pools. Instead, dominant bunchgrasses acquired the most N from all soil N pools. Consistent with these findings we also found that bunchgrasses were the only functional group that inhibited annual grass establishment. At natural levels of species abundance, N partitioning may facilitate coexistence but may not necessarily contribute to N sequestration and invasion resistance by the plant community. This suggests that a general mechanism of invasion resistance may not be expected across systems. Instead, the key mechanism of invasion resistance within a system may depend on trait variation among coexisting species and on how species abundance is distributed in the system.     

Escaping an evolutionary trap: preference and performance of a native insect on an exotic invasive host

Exotic plants may act as population sinks or evolutionary traps for native herbivores. The native butterfly Pieris oleracea lays eggs on garlic mustard, Alliaria petiolata, but larvae develop very poorly on this exotic invasive plant. We examined oviposition preference of individual females and larval performance of their offspring for individuals from one area where garlic mustard is well established and one where it is absent. These data were used to assess whether garlic mustard is being incorporated into or excluded from the diet. Females from the area without garlic mustard showed a wide range of preference, families had low larval survival on garlic mustard, and larval survivorship showed no correlation with mothers’ preferences. Females from the area with garlic mustard preferred it to the native host, and larval survivorship on garlic mustard was positively correlated with the mother’s preference. Individuals surviving on garlic mustard took longer to pupate and weighed >30% less compared to pupae reared on normal hosts. Our results suggest that where garlic mustard is well established P. oleracea may be adapting to this plant by both improved larval performance and increased adult female oviposition preference for it.     

A Zooarchaeological Test for Dietary Resource Depression at the End of the Classic Period in the Petexbatun,Guatemala

Zooarchaeological analyses of animal remains from the Petexbatun sites in the Guatemalan lowlands provide proxy evidence to test a hypothesis of dietary insufficiency during the Maya “collapse.” Ecological foraging theory and resource depression models are used to interpret animal use patterns before and after the disintegration of the Petexbatun polity at the end of the Late Classic period (around a.d. 800). Environmental failure models of the Maya “collapse” at the end of the Late Classic imply that a dietary insufficiency, and particularly a lack of animal resources, was associated with the political and social transitions of this period. However, the results of this zooarchaeological study do not support this hypothesis and point instead to very limited early reductions of only highest-ranked dietary species. The lack of evidence for specific resource depression associated directly with the period of political collapse does not support a model of environmental failure during political disintegration in the Petexbatun. Correlations are found between animal use patterns and the specifics of site size and periods of peak political activity, suggesting that small-scale resource depressions might have resulted at some sites during early periods of human population growth, site expansion, and increasing political activity.     

Genotype by environment interactions for fitness in hybrid genotypes of Avena barbata

We examined genotype (G) by environment (E) interactions for fitness in mesic and xeric ecotypes of the self-fertilizing annual grass, Avena barbata and their recombinant inbred hybrid progeny. Fitness was assayed (1) in experimental water and nutrient treatments in the greenhouse and (2) in common gardens in each ecotype's native habitat. G x E interactions were significant in the greenhouse. Nevertheless, the same recombinant genotypes tended to have high fitness across all water and nutrient treatments. G x E interactions were less pronounced in the field, and were driven by the contrast between the uniformly low survivorship at the mesic site in 2004 and genetic variation in fitness at the other years/site combinations. Moreover, the mesic ecotype consistently outperformed the xeric in both field and greenhouse. Several of the recombinant genotypes outperformed the parents in the novel greenhouse treatments, but these genotypes did not outperform the mesic parent in field trials. Indeed, it is only in the comparison between field and greenhouse environments that there was a noticeable change in the identity of the most-fit genotype. The results provide evidence that hybridization can create genotypes that are better adapted to newer environments such as those imposed in our greenhouse experiments.     

On humans and wildlife in Mediterranean islands

Aim To investigate the effects of human‐induced landscape changes in Mediterranean islands on the ecological and evolutionary responses of bird communities and populations. The combination of mass extinction of large mammals and massive deforestation by humans was hypothesized to produce new selection regimes to which organisms were likely to respond. Habitat selection and niche breadth have been investigated at the scale of species, and phenotypic variation at the scale of local populations. Location The study was carried out along habitat gradients and in habitat mosaics at different spatial scales on the island of Corsica and in areas of similar size and structure in continental France. Methods Two sets of gradients have been used for investigating habitat selection and niche breadth: gradients of altitude, and gradients of vegetation structure. Population studies focused on the blue tit, Cyanistes caeruleus. Large samples of breeding attempts by this species in 10 habitats provided detailed data on phenotypic variation of fitness‐related traits both on Corsica and on the mainland. Results The extent of niche space used by birds differed substantially depending on which habitat gradient was considered. Many species have been found to contract their habitat niche along the elevation gradient on Corsica compared with the mainland, whereas all species in the vegetation gradient broadened their niche on the island. Breeding patterns of the blue tit differed considerably depending on whether they settle in deciduous oaks (Quercus humilis) or in evergreen sclerophyllous oaks (Quercus ilex). Phenotypic variation of breeding traits was much higher on the island, where more populations were correctly timed for the best breeding period than on the mainland, a pattern that is likely to result from lower dispersal of organisms on the island. Main conclusions The differences in observed niche breadth between the two series of habitat gradients is explained both by the species‐specific ecology of the species and the human‐induced environmental history of Corsica. Large‐scale landscape changes provided new opportunities for island colonization by non‐forest species, which are isolated as small, ‘fugitive’ local populations. In both gradients, forest species that are typical components of the Corsican bird fauna definitely expanded their niche and occupied a wider range of habitats on Corsica than on the mainland. At the population scale, landscapes included habitat patches with contrasted selection regimes, which resulted in high phenotypic variation for many fitness‐related traits. Reduced dispersal of birds on the island resulted in a much higher degree of local differentiation on Corsica than on the mainland.     

Descriptive biogeography of Tomicus (Coleoptera: Scolytidae) species in Spain

Aim, location Tomicus (Coleoptera, Scolytidae) species are some of the principal pests of Eurasian forest and are represented by three coexisting species in Spain, Tomicus piniperda (Linnaeus, 1758), Tomicus destruens (Wollaston, 1865) and Tomicus minor (Harting, 1834). The distribution of two taxa are unknown as they have until recently been considered separate species. Therefore, we model the potential distribution centres and establish the potential distribution limits of Tomicus species in Iberia. We also assess the effectiveness of different models by comparing predicted results with observed data. These results will have application in forest pest management. Methods Molecular and morphological techniques were used to identify species from 254 specimens of 81 plots. For each plot, a Geographical Information System was used to extract a set of 14 environmental (one topographic, six climatic) and biotic variables (seven host tree distributions). General Additive Models and Ecological Niche Factor Analysis models are applied for modelling and predicting the potential distribution of the three especies of Tomicus. Results The results of both modelling methodologies are in agreement. Tomicus destruens is the predominant species in Spain, living in low and hot areas. Tomicus piniperda occurs in lower frequency and prefers wet and cold areas of north‐central Spain. We detected sympatric populations of T. destruens and T. piniperda in Northern coast of Spain, infesting mainly P. pinaster. Tomicus minor is the rarest species, and it occupies a fragmented distribution located in high and wet areas. The remarkable biotic variable is the distribution of P. sylvestris, incorporated into the models of T. destruens and T. piniperda. Main conclusions These results indicate that in wet areas of north‐central Spain where T. piniperda occurs (and possibly the high altitudes of the southern mountains), T. destruens has a climatic distribution limit. In the northern border of this area, both species overlap their distributions and some co‐occurrences were detected. Tomicus minor potentially occurs in high and wet fragmented areas.     

Interspecific trophic relationships among pelagic fish species underneath FADs

Fortnightly experimental purse-seine hauls at fish aggregation devices (FADs) and open water control sites, over a 2-year period in oceanic waters o. the eastern coast of Majorca revealed that carangid, coryphaenid, serranid, balistid and centrolophid fishes caught there were mostly planktivores. Most of the species had a high food intake. The dominance of neustonic and holoplanktonic epipelagic prey could indicate a direct link between FADs, invertebrates (biofouling) and fish. Polyprion and Schedophilus were more generalist predators than the more specialized Naucrates and Trachurus spp. There was low variation in feeding intake and the types of prey categories important for each species. Naucrates , Coryphaena and Schedophilus characterized the autumn community under FADs, while Trachurus , Seriola and Balistes were present throughout the summer. There was little diet overlap among the species suggesting only limited competition for the food resources among Trachurus spp, Naucrates and Seriola , and among Seriola and Coryphaena.     

Differences in Species Composition and Feeding Ecology of Catostomid Fishes in Two Distinct Segments of the Missouri River, North Dakota, U.S.A.

In 1997 and 1998, we sampled the Missouri River, North Dakota to determine if anthropogenic disturbances had influenced catostomid species composition and feeding ecology. We compared two distinct river segments, the Missouri River between the mouth of the Yellowstone River and Lake Sakakawea (the Yellowstone–Sakakawea segment (YSS)), a moderately altered segment and the Missouri River between Garrison Dam and Lake Oahe (the Garrison–Oahe segment (GOS)), a highly altered segment. The segments exhibited greatly different sucker communities. Bigmouth buffalo, Ictiobus cyprinellus, smallmouth buffalo, Ictiobus bubalus, and river carpsucker, Carpiodes carpio, represented 94% of the sucker catch in the YSS, whereas in the GOS, white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus, constituted 98% of the sucker catch. In the YSS, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the GOS. Intense anthropogenic disturbances to the GOS are associated with the differences in sucker species composition, prey density and composition, and sucker feeding ecology between the two segments.