Search Results (3)

Lake Bacalar, a fragile oligotrophic ecosystem located in the southeast of Yucatan Peninsula, Mexico, suffered from a sudden brownification after the tropical storm Cristobal in June 2020 in the Gulf of Mexico. The color change was the most visible effect of the storm, but all other water variables changed towards eutrophication. We used light traps and DNA barcoding of the zooplankton specimens based on previous baseline constructed for comparison with the species found after the change. A dramatic shift in the zooplankton community occurred: biomass was reduced to a minimum and 20 species of water mites, five copepods, three cladocerans, three chironomids and six species of fish larvae disappeared for a period of at least one year. They were replaced by three species of water mites, four cladocerans, one copepod, 23 chironomids and one ephemeropteran previously not registered, most of the species being characteristic of more eutrophic environments. The southernmost part of the lake, Laguna Xul-Ha, which conserved its oligotrophic characteristics, apparently became a refuge for the original fauna from the whole system. The ecosystem did not fully recover to its original condition until about two years later. While the system has returned to its original state after the storm described here, future changes in land use, including unsustainable tourism expansion, may compromise its resilience and induce hysteresis. Full article

The distribution of species in relation to latitude and altitude is of fundamental interest to ecologists and is expected to attain increasing importance as the Earth’s climate continues to change. Species diversity is commonly greater at lower than higher latitudes on a global scale, and the similarity of communities frequently decreases with distance. Nevertheless, reasons for such patterns are not well understood. We investigated species richness and changes in community composition of mayflies (Ephemeroptera) over 13 degrees of latitude at 81 locations throughout New Zealand by light-trapping and the benthic sampling of streams. Mayflies were also sampled along an altitudinal gradient on a prominent inactive volcano in the east of North Island. Sampled streams were predominantly in the native forest, at a wide range of altitudes from sea level to c. 1000 m a. s. l. A total of 47 of the 59 described New Zealand mayflies were recorded during the study, along with five undescribed morphospecies. Species richness declined and the degree of dissimilarity (beta diversity) of mayfly communities increased significantly from north to south but less strongly with increasing altitude. Our results suggest that the southward decline in species richness has historical origins with the north of the country having acted as a major refuge and region of speciation during the Pleistocene. The increasing dissimilarity of the northern and southern communities may reflect an increasingly harsh climate, variable amounts of subsequent southward dispersal of northern species and, in the South Island, the presence of species which may have evolved in the newly uplifted mountains during the Miocene–Pliocene. Full article

Studies of connectivity of natural populations are often conducted at different timescales. Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species. In contrast, studies conducted at historical timescales are usually more focused on evolutionary or biogeographic questions. In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera. We conclude that: (1) For both groups, the major mechanism of dispersal is by adult flight, with larval drift playing a very minor role and with unusual patterns of genetic structure at fine scales explained by the “patchy recruitment hypothesis”; (2) There is some evidence presented to suggest that at slightly larger spatial scales (~100 km) caddisflies may be slightly more connected than mayflies; (3) Examinations of three species at historical timescales showed that, in southeast Queensland Australia, despite there being no significant glaciation during the Pleistocene, there are clear impacts of Pleistocene climate changes on their genetic structure; and (4) The use of mitochondrial DNA sequence data has uncovered a number of cryptic species complexes in both trichopterans and ephemeropterans. We conclude with a number of suggestions for further work. Full article