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Natural landscapes nursery
Human activity and eutrophication cause changes in the structure and function of aquatic ecosystems. In response, many populations of aquatic macroinvertebrates and fish species adapt to these conditions. We investigated the influence of complex natural hydrological patterns (as water movement and nutrient input) on the adult survival and reproduction of juvenile amphibians. We also assessed the variation in the response of species at different levels of ecological specialization. The study was conducted in the forested area of the Aziz Canton in Sweden, and we investigated whether these natural disturbances affected survival and reproductive success of aquatic invertebrates and fish. There was a positive association between the frequency of occurrence of different hydrological conditions and the survival of juvenile amphibians. Fish species preferred larger and slower pools, where light and food are distributed more evenly. Species that live in ponds with higher energy levels during the summer (i.e., upper montane, high mountain species) were more tolerant to extreme temperature fluctuations than those in the lower montane and low mountain species. In terms of reproduction, habitat was of greater importance than fish size and duration of residence in a specific habitat. Further studies are required to determine the factors that support species-specific responses to changes in habitat, but these results suggest that the ability to adapt to new conditions is favored by selection acting on dispersal traits, and that these traits are more important for population viability than the habitat quality.These results suggest that the responses of macroinvertebrates and fish species to shifts in the environment may differ, which could explain how the nature of the disturbance influences the species composition and how populations adapt.
The human impact on aquatic ecosystems has increased over the past decade and has been associated with eutrophication, species extinctions and changes in the food web structure. The negative effects of eutrophication on aquatic macroinvertebrates and fish are well documented, but few studies have evaluated how natural disturbances influence these responses. In the present study, we hypothesized that: 1) hydrological conditions are associated with survival and reproductive success of juvenile amphibians, 2) natural disturbances affect species composition, as well as survival and reproductive success of aquatic invertebrates and fish, and 3) the response to disturbances will vary among species of different levels of ecological specialization. We performed a survival and reproduction study in a wild population of salamanders, newts and two species of fish, in a natural landscape where different hydrological patterns, nutrient inputs, land use and climate changes occur. Hydrological disturbances were natural, influenced by weather conditions and water flow.
Materials and methods
Study area and study species
The Aziz Canton is located in the High Ural Mountains, in northern Sweden (55°10′N, 20°28′E). The study area consisted of an upper montane (upper riparian) zone, where forest, shrub, grass and meadow vegetation prevails, and lower montane (lower riparian) and lowland (lake and river) zones. These ecosystems are characterized by a gradient of disturbance that includes traditional anthropogenic disturbances (including high livestock stocking and no-tillage), as well as the lower disturbance levels of natural hydrological events, which cause fluctuations in land and water use.The study area had a surface area of approximately 1,850 ha.
A total of 65 species were recorded, including 30 species of amphibians and 35 species of fish, 23 species being common and 12 species being rare (Richardson et al. 2012). Among the amphibians, there were 35 larvae and 15 adults of the common toad Barbina dorsata. The study species included the newt Triturus vulgaris (Pallas, 1771), a herbivore, and the Northern leopard frog Rana pipiens (Linnaeus, 1758), an omnivore. This species was found in the vegetation and surrounding pools.
In the studied area, natural disturbances were hydrological conditions and land use, and they consisted of large hydrological events with strong changes in flow rate and flow direction. Such natural disturbances were characterized by the following conditions: increasing stream discharge, reduced residence time of the flow in the upper watershed, increased storage capacity, decreased or absent lateral overflow, altered water color and increased turbidity. Two-thirds of the area is covered by forest and grass, with less than 5% of this area receiving considerable anthropogenic activity (e.g., overgrazing by livestock). The remaining area receives less than 5% of the total precipitation (average of ∼500 mm). The lower montane and lowland ecosystems have approximately 50% of the area covered by herbaceous plants and are located on a plateau with lower levels of human disturbance. The upper riparian zone receives ∼25% of the total precipitation, with an average of ∼1,000 mm, and the most frequent annual rainfall period occurs from June to September. Natural disturbances in the upper riparian area are characterized by extremely high flows that originate from snowmelt in the higher elevations and occur in the spring and early summer. Water flow in the watershed is intensified and flows in the stream network are laterally and vertically expanded, which causes extreme shifts in flow direction and increases the residence time.The lower riparian zone receives, on average, ∼1,000 mm of precipitation in the lower montane and lower lowland ecosystems. The average runoff for the upper riparian zone (∼75% of the watershed) is calculated based on measurements performed by the upper riparian and area water regulation authorities in 2010.
The study was conducted during the summer of 2010, when weather conditions ranged from cool to warm with average temperature of 14.5°C. The study was conducted in a total of 24 ponds, which were located in a mature riparian zone dominated by willow and poplar trees, and were grouped into four hydrological conditions: lower flow (no winter and spring flow) (LC1, n = 4), normal flow (regular winter and spring flow) (LC2, n = 5), high flow (winter and spring flow) (LC3, n = 8) and lower flow and streams (LC4, n = 7). Within the study area, differences in