Report of Xiphophorus hellerii in the arid Metztitlán Canyon Biosphere Reserve in Mexico

Biosphere reserves have been established around the world as a means to protect sensitive or threatened ecoregions and the biodiversity within them. As such, the organisms occurring within these reserves are important from a conservation perspective as they often represent endemic species or remnant populations. Here we provide genetic evidence of widespread occurrence of Xiphophorus helleri within the Metztitlán Canyon Biosphere Reserve in Hidalgo, Mexico. One nuclear and two mitochondrial genes were sequenced from four populations within the canyon and confirmed that the specimens collected were X. hellerii. When compared to published sequences of X. hellerii from multiple localities within the documented natural range of the species, the specimens from Metztitlán were found to exhibit between 0 and 1.6 % sequence divergence. Possible scenarios for colonization of the canyon and conservation implications are discussed.     

Proposal for the Establishment of the Core Zones in the Biosphere Reserve of Tehuacán-Cuicatlán, Mexico

This work proposes the establishment of core zones in the Biosphere Reserve of Tehuacán-Cuicatlán (BRTC), based on plant species richness and endemism. A total of 561 species of the four most important plant families in the region (Asteraceae, Cactaceae, Leguminosae and Poaceae) as well as 174 endemic species of these and other families were used in the analyses. Distribution of these taxa was analyzed using two different iterative complementarity methods. Significant correlations were found between patterns of species richness and endemic plants distribution in the study area. These results were combined with other analysis where two different indices (species richness index and human population index) were used. The results suggest the delimitation of four core zones within the Biosphere Reserve, covering a total area of 105,300 ha. The core zones represent 21.8% of the area, and would protect 72.54% of the species from the selected plant families and 67.8% of endemic species.     

Effect of brousse tigrée on the dynamics of nurse–protégé interactions of a cactus in the Chihuahuan Desert

A nurse–protégé relationship is a frequent facilitation interaction in deserts that allows the recruitment of new individuals of many species. Our aim was to evaluate the relationship of Echinocereus enneacanthus during its life cycle and its nurse plants in the brousse tigrée (tiger bush) vegetation of the Chihuahuan Desert. The population structure of the cactus is skewed toward adult stages, which are commonly found in the bare areas of the brousse tigrée, whereas juveniles are located in the vegetated bands. The vegetation structure and the nurse–protégé relationship were determined using censuses of 19 permanent plots monitored between 2008 and 2019. The differential association of E. enneacanthus with potential nurse plants was evaluated using an interaction network, under the hypothesis of strict association of the seedlings and juveniles with nurse species. In addition, χ² tests and standardized residuals were fitted among likely nurse species, weighted by the cover of the nurse and of the areas without vegetation. The study species, as well as the nurse plants, had an aggregated distribution pattern. The interaction network showed that the frequency of the association with nurse plants decreased as the size of the protégé individuals increased. At the same time, there were differences in the establishment of E. enneacanthus under particular nurse plants; Prosopis glandulosa and Hilaria mutica were the most important. The nurse–protégé relationship for seeds and seedlings is integral to the vegetation bands of the brousse tigrée.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species-rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi-deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought-adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization.     

Rarity,ecological memory,rate of floral change in phytoplankton—and the mystery of the Red Cock

In this article, we attempt to estimate the contemporary phytoplankton species pool of a particular lake, by assessing the rate of floral change over a period of 15 years. Phytoplankton time series data from Lake Stechlin, an oligo-mesotrophic lake in the Baltic Lake District (Germany) were used. Of the 254 algal species recorded during the 15-year of studies with roughly biweekly sampling, 212 species were planktonic. In the individual plankton years, the recorded total number of species changed between 97 and 122, of which the number of dominants (>1% contribution to the annual average of total biomass) was only 10–19. The 15-year cumulative number of species exhibited an almost linear increase after an initial saturation phase. This increase was attributed to two reasons: increase of sample size and immigration of species new to the flora. Based on a probabilistic model developed in this study, we estimated the number of co-existing planktonic species of the lake as some 180, and the rate of floral change as 1–2 species per year. Of these co-existing species, only few maintain the matter–energy processing ecosystem functions in any particular plankton year. Selection of these dominants is probably driven by mesoclimatic cycles, coupled with human-induced forcing, like eutrophication. All others are hiding as an ecological memory, in the sense of the capacity or experiences of past states to influence present or future responses of the community. Data analyses suggest that selection of the ‘memory species’ that show temporary abundance increases over shorter (several years) periods are largely dependent upon the dominants. These results show that interspecific interactions and the particular autecological features of the dominants, together with their effects on the whole ecosystem, act as a major organizing force. Some phytoplankton species, like Planktothrix rubescens, are efficient ecosystem engineers with cascading effects of both a top-down and bottom-up nature. Historical scientific data on Planktothrix blooms in Lake Stechlin suggest cyclic patterns in long-term development of phytoplankton which, as the legend of the Red Cock suggests, dates back much further than scientific archives.     

Regeneration patterns in relation to canopy species composition and site variables in mixed oak forests in the Sierra de Manantlán Biosphere Reserve, Mexico

Regeneration patterns in relation to canopy species composition and site variables were analyzed in mixed oak forests of the Sierra de Manantlán in western Mexico with the aim of establishing an ecological basis for the design of management alternatives. Using ordination (canonical correspondence analysis) and classification (two-way indicator species analysis) methods, five different canopy types and three different seedling associations were revealed according to species composition, all of them dominated by one or more oak species. Red–far red ratio, slope, altitude, topography, canopy type and grazing intensity were the main variables that explained differences in species composition among the seedling associations. Oak seedlings were relatively scarce in the sampling plots, with the lowest frequency values of all species recorded except for those of Quercus crassipes Humb. & Bonpl., and also the lowest density values. The presence of a particular oak seedling species was strongly associated with a particular percentage of canopy openness; Quercus candicans Née, Quercus laurina Humb. & Bonpl. and Quercus rugosa Née were present in the plots with the least-open canopy (6.4%, 2.9 and 6.2%, respectively), while Quercus castanea Née and Quercus crassipes Humb. & Bonpl. were present in the plots with the most-open canopy (13 and 8.1%, respectively). Every oak seedling species was more frequent, although not dependent, on the canopy type where the same oak species dominated. Because of the great heterogeneity in species composition and the physiographical factors of mixed oak forests in the Sierra de Manantlán, we concluded that management alternatives must be prescribed for each ecological situation where the different oak species are growing.     

Non-timber forest products in the community of El Terrero, Sierra de Manantlán Biosphere Reserve, Mexico: Is their use sustainable?

The importance of non-timber forest products (NTFPs) to rural income was examined in a highland community in the Sierra de Manantlán Biosphere Reserve, Jalisco-Colima, Mexico. Rapid Rural Appraisal (RRA) techniques were used to interview 70% of households in the community of El Terrero. Of the nine plant species identified as NTFP sources, the two principal species traded by the community were tila (derived from the flowers and fruits of the tree Ternstroemia lineata), and blackberry (Rubus spp.). Collecting and selling of NTFPs was almost exclusively undertaken by women, with 80% of respondents participating. NTFP sale ranked as the most important source of cash income for 30% of women interviewed, and either second- or third-most important for the remainder. The research examined harvesting impact on populations of T. lineata, an understory tree species characteristic of cloud forest, which this was assessed in the four most-frequented collecting sites. Our results suggested that current harvesting approaches appear to be sustainable, although 95% of the women interviewed reported a decline in resource availability within the last 15 years, apparently resulting from illegal cutting. Suggestions are made with respect to the sustainable development of NTFP resources to help alleviate poverty within the Reserve.     

Birds as marine–terrestrial linkages in sub-polar archipelagic systems: avian community composition, function and seasonal dynamics in the Cape Horn Biosphere Reserve (54–55°S), Chile

Marine environments are known to affect adjacent terrestrial biotic communities. In South America’s sub-Antarctic archipelago, birds are the most abundant and diverse terrestrial vertebrate assemblage. We hypothesized that birds would reflect a marine influence that would gradually decrease inland, expecting to find greater species richness, abundance, and biomass near the sea with decreases toward the island interior. We seasonally compared these parameters, with identified indicator species and assessed functional groups at 0, 150, and 300 m from the coast. Unexpectedly, we found a marked marine (0) and terrestrial (150–300) patterns for avian assemblages, rather than a gradient. In addition, seasonal patterns were warm (spring–summer) and cold (autumn–winter). The only parameter that displayed a true gradient was avian biomass in spring. During the cold season, higher values were observed in all variables for coastal assemblages, compared to inland sites. In the warm season, abundance and richness of coastal and terrestrial assemblages were similar, owing to migratory species. Milvago chimango was the only species abundant and frequent in both terrestrial and coastal systems, thereby indicating potential as a marine–terrestrial vector. Functionally, coastal assemblages were conformed of herbivores, carnivores, and scavengers, while terrestrial communities were made up of omnivores and insectivores. We conclude that the sea coast is a unique habitat in this archipelago, providing refuge for both marine and terrestrial sub-Antarctic birdlife particularly in the cold season. The relevance of the land/sea ecotone is poorly known, but important is given to high demand for the installation of salmon aquaculture facilities along the southern Chilean coastline.     

Species introduction in restoration projects – Evaluation of different techniques for the establishment of semi-natural grasslands in Central and Northwestern Europe

During recent decades, many studies have shown that the successful restoration of species-rich grasslands is often seed-limited because of depleted seed banks and limited seed dispersal in modern fragmented landscapes. In Europe, commercial seed mixtures, which are widely used for restoration measures, mostly consist of species and varieties of non-local provenance. The regional biodiversity of a given landscape, however, can be preserved only when seeds or plants of local provenance are used in restoration projects. Furthermore, the transfer of suitable target species of local provenance can strongly enhance restoration success.We review and evaluate the success of currently used near-natural methods for the introduction of target plant species (e.g. seeding of site-specific seed mixtures, transfer of fresh seed-containing hay, vacuum harvesting, transfer of turves or seed-containing soil) on restoration sites, ranging from dry and mesic meadows to floodplain grasslands and fens. Own data combined with literature findings show species establishment rates during the initial phase as well as the persistence of target species during long-term vegetation development on restoration sites.In conclusion, our review indicates that seed limitation can be overcome successfully by most of the reviewed measures for species introduction. The establishment of species-rich grasslands is most successful when seeds, seed-containing plant material or soil are spread on bare soil of ex-arable fields after tilling or topsoil removal, or on raw soils, e.g. in mined areas. In species-poor grasslands without soil disturbance and on older ex-arable fields with dense weed vegetation, final transfer rates were the lowest. For future restoration projects, suitable measures have to be chosen carefully from case to case as they differ considerably in costs and logistic effort. Long-term prospects for restored grassland are especially good when management can be incorporated in agricultural systems.     

Comparing the conservatism of ecological interactions in plant–pollinator and plant–herbivore networks

Conservatism in species interaction, meaning that related species tend to interact with similar partners, is an important feature of ecological interactions. Studies at community scale highlight variations in conservatism strength depending on the characteristics of the ecological interaction studied. However, the heterogeneity of datasets and methods used prevent to compare results between mutualistic and antagonistic networks. Here we perform such a comparison by taking plant–insect communities as a study case, with data on plant–herbivore and plant–pollinator networks. Our analysis reveals that plants acting as resources for herbivores exhibit the strongest conservatism in species interaction among the four interacting groups. Conservatism levels are similar for insect pollinators, insect herbivores and plants as interacting partners of pollinators, although insect pollinators tend to have a slightly higher conservatism than the two others. Our results thus clearly support the current view that within antagonistic networks, conservatism is stronger for species as resources than for species as consumer. Although the pattern tends to be opposite for plant–pollinator networks, our results suggest that asymmetry in conservatism is much less pronounced between the pollinators and the plant they interact with. We discuss these differences in conservatism strength in relation with the processes structuring plant–insect communities.     

Sociocultural and ecological factors influencing management of edible and non-edible plants: the case of Ixcatlán,Mexico

Background

Identifying factors influencing plant management allows understanding how processes of domestication operate. Uncertain availability of resources is a main motivation for managing edible plants, but little is known about management motives of non-edible resources like medicinal and ceremonial plants. We hypothesized that uncertain availability of resources would be a general factor motivating their management, but other motives could operate simultaneously. Uncertainty and risk might be less important motives in medicinal than in edible plants, while for ceremonial plants, symbolic and spiritual values would be more relevant.

Methods

We inventoried edible, medicinal, and ceremonial plants in Ixcatlán, Oaxaca, Mexico, and conducted in-depth studies with 20 native and naturalized species per use type; we documented their cultural importance and abundance by interviewing 25 households and sampling vegetation in 33 sites. Consumption amounts and preferences were studied through surveys and free listings with 38 interviewees. Management intensity and risk indexes were calculated through PCA and their relation analyzed through regression analyses. Canonical methods allowed identifying the main sociocultural and ecological factors influencing management of plants per use type.

Results

Nearly 64, 63, and 55% of all ceremonial, edible, and medicinal wild plants recorded, respectively, are managed in order to maintain or increase their availability, embellishing environments, and because of ethical reasons and curiosity. Management intensity was higher in edible plants under human selection and associated with risk. Management of ceremonial and medicinal plants was not associated with indexes of risk or uncertainty in their availability. Other sociocultural and ecological factors influence management intensity, the most important being reciprocal relations and abundance perception.

Conclusions

Plant management through practices and collectively regulated strategies is strongly related to control of risk and uncertainty in edible plants, compared with medicinal and ceremonial plants, in which reciprocal interchanges, curiosity, and spiritual values are more important factors. Understanding how needs, worries, social relations, and ethical values influence management decisions is important to understand processes of constructing management strategies and how domestication could be started in the past and are operated at the present.

     

Soil–litter mixing and microbial activity mediate decomposition and soil aggregate formation in a sandy shrub-invaded Chihuahuan Desert grassland

Drylands account globally for 30% of terrestrial net primary production and 20% of soil organic carbon. Present ecosystem models under predict litter decay in drylands, limiting assessments of biogeochemical cycling at multiple scales. Overlooked decomposition drivers, such as soil–litter mixing (SLM), may account for part of this model-measurement disconnect. We documented SLM and decomposition in relation to the formation of soil-microbial films and microbial extracellular enzyme activity (EEA) in the North American Chihuahuan Desert by placing mesh bags containing shrub (Prosopis glandulosa) foliar litter on the soil surface within contrasting vegetation microsites. Mass loss (in terms of k, the decay constant) was best described by the degree of SLM and soil-microbial film cover. EEA was greatest during periods of rapid litter decomposition and associated SLM. Soil-microbial film cover on litter surfaces increased over time and was greater in bare ground microsites (50% litter surface area covered) compared to shrub and grass microsites (37 and 33% covered, respectively). Soil aggregates that formed in association with decomposing leaf material had organic C and N concentrations 1.5–2× that of local surface soils. Micrographs of soil aggregates revealed a strong biotic component in their structure, suggesting that microbial decomposition facilitates aggregate formation and their C and N content. Decomposition drivers in arid lands fall into two major categories, abiotic and biotic, and it is challenging to ascertain their relative importance. The temporal synchrony between surface litter mass loss, EEA, biotic film development, and aggregate formation observed in this study supports the hypothesis that SLM enhances decomposition on detached litter by promoting conditions favorable for microbial processes. Inclusion of interactions between SLM and biological drivers will improve the ability of ecosystem models to predict decomposition rates and dynamics in drylands.     

Cultural,economic, and ecological factors influencing management of wild plants and mushrooms interchanged in Purépecha markets of Mexico

Background

Traditional markets outstandingly contribute to conservation of biocultural diversity, social relations, and cultural values. These markets reflect life strategies and forms people of a region interact with their biodiversity and territories, as well as traditional ecological knowledge and management practices. To understand the factors motivating plant and mushroom management, we analyzed the resources cultural and economic values, their role in people’s subsistence, and the relation of these values with the resources spatial and temporal availability. Our study based on the supposition that traditional markets are settings of interchange of resources with the highest importance for people’s life in a region. Also, that the cultural, economic, and ecological factors influence values of the resources, and the demand on them determine pressures on the most valuable resources which, when scarce, motivate management innovation, otherwise become extinct.

Methods

We documented cultural, economic, and ecological aspects, as well as management techniques of wild and weedy plants and mushrooms interchanged in three traditional markets of the Pátzcuaro Lake region, in central-western Mexico. For doing that, from February 2015 to March 2018, we conducted 175 visits to markets and 89 semi-structured interviews to producers, gatherers, and sellers of wild and weedy plants and mushrooms. Based on participant observation and interviews, we identified variables related to culture, economic, and ecological aspects, as well as management regimes of resources and management systems, which were documented and used as indicators for quantitative analyses. Through principal components analyses (PCA), we determined the indexes of cultural and economic importance (ICEI), management intensity (IMI), and ecological risk (IR) of the resources studied. For conducting that, we classified plant and mushroom species according to their cultural, economic, ecological, and technological indicators, respectively. The score of the first principal component was considered as the index for each group of variables, respectively. To identify relations between cultural importance and risk, we performed linear regression analyses between ICEI and IR indexes.

Results

We recorded 57 species of wild and weedy plants used as food, medicine, and ornamental, and 17 species of edible mushrooms. The variables with the highest weight in the ICEI are related to the need of a resource according to people, its recognizing, the number of communities and markets offering it in markets, its explicit preference expressed by people, the effort invested in obtaining it, and the form it is interchanged. Gathering is practiced in all mushrooms and wild and weedy plants from forests and agricultural areas; 11 species in addition receive 1 or more forms of management (enhancing, selective let standing, propagation through seeds or vegetative parts, transplantation, and/or protection). The management intensity and complexity are explained by variables related to management practices and systems. Plants receiving selective management have the higher management intensity. Silvicultural management (in situ management in forests) was recorded in all species of mushrooms, as well as in more than 80% of medicinal, ceremonial and ornamental plants, and in more than 50% of the edible plants. In agricultural systems, people manage more than 90% of the edible plants recorded to be under a management regime, 25% of the managed medicinal plants, and 30.7% of the managed ceremonial and ornamental plants. In homegardens, people manage 41.6% of the medicinal plants recorded and 26.6% of the edible plants, to have them available near home. Nearly 63% of the species interchanged in the markets studied are gathered in forests without any other management form. In this group are included all mushroom species, 61.5% of ceremonial/ornamental plants, 50% of medicinal, and 33.3% of edible plants. The linear regression between ICEI an IER is significantly negative for edible species with high management intensity R²?=?0.505 (p?=?0.0316), because of their management. But in medicinal and ornamental plants, the risk is high if the cultural importance increases, even when management practices like transplanting and propagation in homegardens are carried out.

Conclusions

Traditional markets are settings of interchange of products, knowledge, and experiences, where the ongoing factors and processes motivating management innovation can be identified and documented. This approach allows documenting processes occurring at regional level but would be benefited from deeper studies at local level in communities.

     

The composition,structure, and dynamics of the nekton of the upper epipelagic layer in the Aleutian and Commander basins,western Bering Sea,in the fall seasons of 2002–2013

The data on the composition and abundance of nekton species and their interannual variations within the upper epipelagic layer (0–50 m) in the Aleutian and Commander basins in the western Bering Sea that are considered in the article were collected during complex surveys that were conducted by the Pacific Research Fisheries Center in September and October of 2002–2013. The core species structures of the nekton communities in these two areas were similar: the chum salmon Oncorhynchus keta and the boreopacific gonate squid Boreoteuthis borealis were the most abundant species. Simpson’s dominance index varied synchronously in both areas, with higher values in the Aleutian Basin, until 2009. In the subsequent years, the values of the index for the studied areas became equal and varied asynchronously. An analysis of abundance showed that two types of species structure most often prevailed (with the dominance of either chum salmon or squid); in some years the species structure differed from that in other years. Species of the low-boreal and low-boreal-subtropical complexes were more abundant in the Commander Basin, reaching particularly high proportions in 2006, 2008, and 2012. Certain species showed similarity in the year-to-year dynamics of their abundance; however, these coincidences were frequently accidental. After the climate regime shift in 2006–2007, the total biomass of nekton in the Aleutian Basin decreased from 3241 to 1736 kg/km² (46%); in the Komandorskiye Basin it decreased from 2459 to 1976 kg/km² (20%).     

Spatiotemporal dynamics of duck harvest distributions in the Central and Mississippi flyways, 1960–2019

Geographical distributions of waterfowl exhibit annual variation in response to spatiotemporal variation in weather conditions, habitat availability, and other factors. Continuing changes in climate and land use could lead to persistent shifts of waterfowl distributions, potentially causing a mismatch with habitat conservation planning, wetland restoration efforts, and harvest management decisions informed by historical distributions. We used band recoveries and harvest records (i.e., hunter-harvested wings) from the United States Fish and Wildlife Service Waterfowl Parts Collection Survey as indices of duck distribution in autumn and winter, and quantified intra-annual, interannual, and interspecific variation in their geographic distributions across 6 decades (1960–2019) for 15 duck species in the Central and Mississippi flyways in North America. Specifically, we tested for annual and decadal shifts in mean latitude and longitude of recoveries for each month (Oct–Jan) by species and taxonomic guild (i.e., dabbling, diving ducks). Overall, species varied in the extent, timing, and sometimes direction, of distributional change in recoveries. From 1960–2019, mean recovery locations for dabbling ducks shifted south 105–296 km in October and 27 km in November (wings only), whereas mean latitudes shifted north 144–234 km in December and 186–301 km in January. Mean recovery locations for diving ducks shifted north 162 km in October (wings only), 84–173 km in December, and 66–120 km in January, but shifted 99–512 km south in November. Shifts in longitude were less consistent between guilds and data types. Finally, distributional change rarely accelerated during recent decades, except for southward shifts of band recoveries of diving ducks in November and northward shifts of band and wing recoveries of dabbling ducks in January. Although anecdotal accounts of large-scale northward shifts in duck distributions are prolific in the land management and hunting communities, our data demonstrate more subtle shifts that vary considerably by species and month. Observed changes in recovery distributions could necessitate changes in timing of habitat management practices throughout the Central and Mississippi flyways and may result in fewer hunting and recreational opportunities for some species in southern states. Quantifying patterns of historical change is a necessary first step to understanding temporal and interspecific variation in waterfowl distributions, which will help with landscape-scale conservation and management efforts in the future and enable effective communication to core constituencies regarding ongoing changes and their implications for recreational engagement.     

Export agriculture,transnational farmworkers,and labor resistance in the Mexico–US borderlands

This article discusses the system of export agriculture in northern Mexico and its impact on transnational farmworkers employed in both sides of the US–Mexico border. Since the late 1990s, a transnational industry producing fresh produce for consumer markers in the USA has taken hold in the San Quintin Valley in Baja California, transforming the economic and social fabric of this border region. This industry has generated a new labor regime predicated upon the employment of a flexible and cheap source of indigenous workers from the poorest states in southern Mexico. I examine the contours of this regime, the forms of labor resistance it has elicited, and the new types of labor migration it has generated by Mexican workers to the USA. As I show, indigenous farm laborers engage in novel forms of labor and political protests to claim for their rights. These developments, I argue, speak of the class formation of transnational farmworkers who, mobilizing local and transnationally, combine traditional labor demands with wider claims for their civil and political rights.     

Roles of dispersal, stochasticity, and nonlinear dynamics in the spatial structuring of seasonal natural enemy–victim populations

Natural enemy–victim systems may exhibit a range of dynamic space–time patterns. We used a theoretical framework to study spatiotemporal structuring in a transient natural enemy–victim system subject to differential rates of dispersal, stochastic forcing, and nonlinear dynamics. Highly mobile natural enemies that attacked less mobile victims were locally spatially segregated from each other when governed by approximate linear dynamics. In contrast, in nonlinear dynamical systems, such as cyclic populations, interacting species achieved local aggregation with each other regardless of dispersal rates, and aggregation was enhanced specifically when highly mobile enemies attacked less mobile victims. These patterns of spatial aggregation held under varying levels of stochastic forcing. This work thus shows a range of dynamic spatial patterns in interacting-species models, and how spatial aggregation between natural enemies and victims can be achieved in locally unstable populations that are linked through dispersal.     

Calculation of the Ecological Risk Index in the José Antonio Alzate Dam, State of Mexico, Mexico

Due to the problem of contamination in the Jose Antonio Alzate dam, located in the State of Mexico, Mexico, the partition coefficient, the contamination degree, and the ecological risk index of nine metals were calculated in order to establish the water quality in different areas of the Alzate dam. The sampling sites were selected according to the river flow into the dam, via three sampling programs, the physical–chemical parameters were measured in situ, and the samples were collected to measure metals in the dissolved phase and also as suspended particulate matter. Thomann’s model was used to calculate the partition coefficient. Håkanson’s methodology was used to determine the degree of contamination and the ecological risk index. Finally, the water quality criteria for the dissolved metals were calculated. The results for suspended particulate matter suggest a moderate risk of metal contamination in the dam. Copper and lead in dissolved form exceeded the values of water quality criteria.     

Travel costs, oviposition behaviour and the dynamics of insect–plant systems

Insect attack can have major consequences for plant population dynamics. We used individually based simulation models to ask how insect oviposition behaviour influences persistence and potential stability of an herbivore–plant system. We emphasised effects on system dynamics of herbivore travel costs and of two kinds of behaviour that might evolve to mitigate travel costs: insect clutch size behaviour (whether eggs are laid singly or in groups) and female aggregation behaviour (whether females prefer or avoid plants already bearing eggs). Travel costs that increase as plant populations drop lead to inverse density dependence of plant reproduction under herbivore attack. Female clutch size and aggregation behaviours also strongly affect system dynamics. When females lay eggs in large clutches or aggregate their clutches, herbivore damage varies strongly among plants, providing probabilistic refuges that permit plant reproduction and persistence. However, the population dynamics depend strongly on whether insect behaviour is fixed or responds adaptively to plant population size: when (and only when) females increase clutch size or aggregation as plants become rare, refuges from herbivory weaken at high plant density, creating inverse density dependence in plant reproduction. Both herbivore travel costs themselves, and also insect behaviour that might evolve in response to travel costs, can thus create plant density dependence—a basic requirement for regulation of plant populations by their insect herbivores.