Rodrigo Moncayo-Estrada

Trophic interactions among sympatric zooplanktivorous fish species in volume change conditions in a large, shallow, tropical lake

Significant reductions in the water volume of shallow lakes impose a restriction on species segregation promoting more interactions in the trophic relationships. The diets of three closely related zooplanktivorous silversides belonging to the Atherinopsidae species flock of lake Chapala , Mexico, were analyzed at two sites (Chirostoma jordani, C. labarcae, and C. consocium). Diets were described in critical shallow (August 2000) and volume recovery conditions (August 2005). Diets included mainly cladocerans (Bosmina, Ceriodaphnia, and Daphnia) and copepods (Cyclops). A significant difference in diets was detected when comparing years (MRPP analysis, A = 0.22, p < 0.0001) and sites at different years (MRPP analysis, A = 0.17, p = 0.004). According to niche breadth mean values, species were classified as specialized and intermediate feeders. In shallow conditions, the small range of niche breadth (1.72 to 3.64) and high diet overlap values (D = 0.64, L = 8.62) indicated a high potential for interspecific exploitative interaction. When the lake volume recovered, an increase in the niche breadth range (1.04 to 4.96) and low niche overlap values (D = 0.53, L = 2.32) indicated a reduction of the species interaction. The Mann-Whitney U-test supported this pattern by showing a significant difference between years for niche overlap (p = 0.006). The increased interaction during the low volume suggests alternative segregation in life-history variations and other niche dimensions such as spatial or temporal distribution.

Fish Fauna of Lake Chapala

Lake Chapala is one of the most important reservoirs, which reflects the origin, evolution, and biogeography of freshwater fish fauna in central Mexico. It is the area where more diversity of the endemic subfamily of Goodeinae (“pintillas” and “tiros”), with nine species, is found. This zone outstands for the evolution and sympatric specialization of “charales” and “pescados blancos”, (Atherinidae) which include eight species. It is also the habitat of endemic “bagres” (Ictaluridae), different native carps (Cyprinidae), and historically, it served as the habitat of lampreys (Petromyzontidae). The ichthyofauna of the lake is also very important, at least seventeen of the species provide on-the-spot work of artisan fishery for 1,699 fishermen belonging to 86 fisheries’ co-operatives, and is the local and regional food source. Unfortunately, Lake Chapala presents a high level of environmental degradation, due to a profound modification of the ecosystem. As a result of this fact we can confirm the actual presence of 27 out of 39 registered species, including both native and exotic. Likewise, before 1990 there were high-volume captures (13,710.78 tons per year), however the present production has decreased by a factor of ten. The aforementioned problem cannot be attributed to a single cause, but to a synergetic effect that involves different factors combined with the lack of regulation and pursuit of plans for sustainable development. A contemplated conservation initiative for the restoration of the lake is not the best way to solve the problem. Recommendations are formulated regarding future studies and activities on the situation of the ichthyofauna in the lake.

Long-term change in the biotic integrity of a shallow tropical lake: A decadal analysis of the Lake Chapala fish community

Abstract We describe the successful application of a 4-decade analysis of an Index of Biotic Integrity (IBI) demonstrating its assessment value when applied to the fish community of Lake Chapala. We based our analysis on fish community and fishery composition and on the proportion and density of native and exotic species for each decade. Fisheries landings and IBI values document a long-term downward trend since the 1970s. Data from the 1990s and 2000s reveal a dramatic drop in the IBI score to 20 points (out of a possible 100), a rating of very poor. The fisheries collapse and the loss of 11 native species as a consequence of habitat degradation and invasive species have reduced native fish biomass and richness. Fluctuations in rainfall, principally, and water-extraction related to human activities have had a major impact on the lake. Additionally, water quality deterioration has been caused by a lack of wastewater treatment. The fish community has been further modified by large increases in the number and biomass of exotic fishes. Although the exact degree of decline in biotic integrity is impossible to determine because of uncertainty about the representativeness and accuracy of some historical information, the analysis of the temporal changes in the IBI provides compelling evidence for an accelerating drop in ecosystem health. The application of IBI, which is broad in scope and has flexible data requirements, can serve as a template for assessing trends in other water bodies with a history of fisheries data but limited standardized monitoring of the fish community.

Spatial patterns of zooplanktivore Chirostoma species (Atherinopsidae) during water-level fluctuation in the shallow tropical Lake Chapala, Mexico: seasonal and interannual analysis

This study addresses the influence of water-level fluctuations on fish distribution at two temporal scales: seasonal (dry and rainy) and interannual (low and high volume conditions). The analysis of abundance relationships among three zooplanktivore Chirostoma species at fifteen sites in Lake Chapala, Mexico, revealed the significant influence of contrasting conditions (P=0.0002). Seasonally, segregation was more related to species dominance in the dry season and exclusively related to environmental characteristics in the rainy season. Interanually, biotic influence occurred in the shallowest and the deepest episodes of the lake. Environmental characteristics influenced species distribution when the lake reached 25% of its volume. Site, depth, temperature, and salinity were the leading factors influencing fish distribution. These results emphasize the necessity to implement different management strategies according to lake volume, particularly when a critical threshold is reached.

DIET OF CHIROSTOMA LUCIUS (PISCES: ATHERINOMORPHA): SEASONAL TROPHIC SPECTRUM AND ONTOGENY OF PISCIVORY

Abstract We determined the diet of Chirostoma lucius from Lake Chapala and Guaracha Reservoir in central Mexico by stomach content analysis. Diet consisted primarily of juveniles of small Chirostoma species, as well as cladocerans and copepods. Seasonal change in prey showed high fish consumption in the rainy period, whereas crustacean consumption increased in the dry period. Diet varied with size, with smaller fish selecting large numbers of small zooplankton prey, whereas the largest size classes fed principally on fish. The size for the shift to piscivory was smaller in Lake Chapala (10 cm) than Guaracha Reservoir (14 cm), and the value for the pooled data of both populations was 12 cm.

EL FENÓMENO DE CAMBIO CLIMÁTICO EN LA PERCEPCIÓN DE LA COMUNIDAD INDÍGENA PURÉPECHA DEL MUNICIPIO DE CHILCHOTA, MICHOACÁN, MÉXICO

The aim of this research was to estimate the perception or knowledge about the phenomenon of climate change in the Purepecha’s indigenous population in the Municipality of Chilchota, Michoacan, Mexico. The latter, taking into account some adaptation mechanisms that the stakeholders may have, based on their current culture, traditions and knowledge. Different surveys were applied as a tool to obtain information. A total of 298 surveys were carried out and distributed in four communities of the municipality: Zopoco (49), Tanaquillo (50), Carapan (59), Ichan (37) and the municipal head Chilchota (103). Multivariate techniques were applied on the surveys to reduce the data structure into groups of variables. Results show that the indigenous population of the Chilchota municipality perceives local changes in the climate attributed to several anthropogenic actions developed in recent years (logging, trash burning, pollution, etc.). They do not associate such changes with the phenomenon of climate change. Agricultural planting schedules in the region have been adjusted as an adaptive measure to the perceived changes. These climate changes are consistent with the average annual temperature and precipitation behavior for the 1968-2007 periods. For this period the temperature showed an increase of 0.5 oC, meanwhile precipitation was reduced to 150 mm per year.

Nitrogen nutrients in a subtropical river: temporal variation and analysis at different spatial scales

Herein we provide a framework for evaluating the spatiotemporal variation of nitrate and ammonium and their relationships with environmental and anthropogenic variables at different scales. Bimonthly samples were collected from 28 sites in the Duero River, Mexico, from May to December 2013. The river flow changed and lost connectivity during the dry season because more water was diverted for irrigation. Four sites had the highest nitrate and ammonium values (7.6 and 22.1mgL–1 respectively), which were related to direct waste water discharge. The remaining 24 sites were analysed using a multivariate approach. Using hierarchical cluster analysis, seasonal trends were identified with two groupings during July and five in December. Sites were grouped into those with constant discharge and nitrates affected by springs and those with poor water quality (high concentrations of ammonium). Non-metric multidimensional scaling simultaneously revealed the variation in time and space, organised sites into an environmental ammonium gradient and differentiated between seasons according to nitrate levels. Regression tree analysis established a relationship between nutrients and independent variables. At the landscape level, the agricultural area affected nitrate (75%) and urban area affected ammonium (45%); at the basin level, road density influenced both parameters (10.68km per 25km2).

Environmental Degradation in a Eutrophic Shallow Lake is not Simply Due to Abundance of Non-native Cyprinus carpio.

Non-native species are often major drivers of the deterioration of natural ecosystems. The common carp Cyprinus carpio are known to cause major changes in lentic systems, but may not be solely responsible for large scale changes in these ecosystems. We used data from extensive collection efforts to gain insight into the importance of carp as drivers of ecosystem change in Lake Patzcuaro, Mexico. We compared the structure (fish density, biomass, diversity, and evenness) of fish assemblages from six Lake Patzcuaro sites with different habitat characteristics. Intersite comparisons were carried out for both wet and dry seasons. We explored the relationships between non-carp species and carp; and studied multivariate interactions between fish abundance and habitat characteristics. From a biomass perspective, carp was dominant in only four of six sites. In terms of density, carp was not a dominant species in all sites. Further, carp density and biomass were not negatively related to native species density and biomass, even when carp density and biomass were positively correlated to water turbidity levels. Carp dominated fish assemblages in the shallowest sites with the highest water turbidity, plant detritus at the bottom, and floating macrophytes covering the lake surface. These results suggest that the effect of carp on fish assemblages may be highly dependent on habitat characteristics in Lake Patzcuaro. Watershed degradation, pollution, water level loss, and other sources of anthropogenic influence may be more important drivers of Lake Patzcuaro degradation than the abundance of carp.

Threatened fishes of the world: Hubbsinna turneri (De Buen, 1941) (Goodeidae)

Keywords Goodeidae.CentralMexico.ZacapuLake.EndangeredCommon name: Cherehuita. Conservation status:Endemic, endangered, NOM-059-ECOL-2001 (DOF2002). Should be included in Appendix 1 of CITES ascritically endangered according to the IUCN criteria(Dominguez-Dominguez et al. 2008). Identification:Differs from the other Goodeinae by the presence of30–37 dorsal rays. Drawing by Aslam Narvaez-Parra(UAQ). Recently, Hubbsina was proposed as asynonym of Girardinichthys and H. turneri as adifferent species, Girardinichthys ireneae (Raddaand Meyer 2003). We do not agree with theseproposals, according to molecular and taxonomicstudies (Moncayo-Estrada 1993;DoadrioandDominguez-Dominguez 2004). Distribution: CuitzeoLake basin, Michoacan (without records since 1980)and currently restricted to Zacapu Lake Basin,Michoacan. Type locality: Cointzio, Michoacan,Mexico. Abundance: low: in Zacapu Lake comprising9.7% of total fish numbers (0.076 individuals·m

Historical Delineation of Landscape Units Using Physical Geographic Characteristics and Land Use/Cover Change

Abstract Landscape units are conceived as a part of the territory that share similar physical and geographic characteristics. Their delineation can contribute to identify the physical and social dynamics that emerge in the spatial environment and to propose strategies of planning and management of the territory. The main objective was to make a historical delineation of landscape units in the Duero river basin that demonstrate the dynamics of changes in the territory, the description of the actors involved, and the affectations in the natural and social environment. We analyzed the vegetation change and urban growth from 1983 to 2014, incorporating climatic, edaphic, and topographic variables. A Principal Component Analysis was performed with the information and results were used in Maximum Likelihood procedure to define different clusters based on environmental characteristics. We defined five categories from the Landsat images. Results showed landscape units with homogeneous environmental characteristics and some differences in the units’ delineation were mainly influenced by political and socioeconomic factors. Temporally there was an increased tendency of landscape units, three in 1983, nine in 1990, 1995, 2000 and 2011, and eight in 2014. This increase resulted from territory fragmentation because of berries and avocado cultivars expansion over wooded area.