Ecology of Freshwater Fish最新文献

Heterospecific sociability could enhance invasion success in social species since social non-natives usually belong to small founding populations during the early stages of invasion. The twospot livebearer (Pseudoxiphophorus bimaculatus) is native to Central America and southern Mexico and is recently recognised as invasive in the Mexican Central Plateau, where it poses a threat to native species. Here, we evaluated twospot livebearer sociability towards either a conspecific pair or a shoal of four fish with one of four possible compositions, all conspecifics or two conspecifics combined with either two guppies, two porthole livebearers or two twoline skiffias. In a second experiment, foraging time, latency to feed, first fish to begin foraging and aggressive interactions were recorded under the same social conditions used in the sociability experiment, with body size included as a covariate in both experiments. All focal twospot livebearers spent significantly more time with the given shoals rather than with the available space in the aquarium. They showed a higher tendency to associate with small shoals of conspecifics than with pairs. Larger twospot livebearers associated more, regardless of the social condition. Twospot livebearer fed more with porthole livebearers, less with guppies and similarly with twoline skiffias. Latency to forage did not vary significantly between social conditions. Twospot livebearers were involved in more aggressive interactions when with guppies or porthole livebearers than when with native twoline skiffias or conspecifics. Twospot livebearers could gain benefits from associating with natives and conspecifics, but not with other invasive poeciliids. Heterospecific shoaling behaviour with natives may enhance invasion success during early stages when conspecifics are scarce while associating with other invasive poeciliids could lead to increased competition. Further research is needed on heterospecific interactions of non-natives to better understand their behavioural role in invasion likelihood.

Mixing processes in lakes are important in determining sedimentation zones and in setting the so-called “wash zone”, the area of lake bottom in contact with an oscillating thermocline during wind-driven internal seiche events. The wash zone also aligns with a sharp change in sediment roughness and hardness. Taken together, these rapid changes in temperature and sediment indicate that the wash zone is a distinctive ecotone in stratified lakes. Depth stratified randomised netting was used to develop count-based habitat use models for three common benthic fish species as a function of depth or temperature covariates. Using data from two lakes with quite different wash zone depths, we show the wash zone to describe fish habitat for two of three benthic fish species by utilising the top 50% of estimated fish abundance as an indicator of habitat use. White sucker (Catostomus commersoni) habitat use was within the boundaries of the wash zone. Lake whitefish (Coregonus clupeaformis) habitat was adjacent and within the wash zone. Longnose sucker (C. catostomus) habitat use was in the deep areas of lakes dominated by sediment focusing and did not overlap white sucker. Lake whitefish habitat use overlapped both catostomids, but peak abundance of both lake whitefish and white sucker overlapped pointing to potential interactions between these species. Smaller lakes have less vigorous mixing processes and a narrower wash zone, so with a decline in lake size the likely area of the wash zone as habitat for benthic feeding fish would become smaller.

Fish assemblages in freshwater ecosystems are becoming more homogenous from multiple abiotic, environmental, and physicochemical variables at different scales. Historical fish collections (1976–1977) by Billy Michael Johnson and Dr. Johnson K. Beadles were compared to contemporary fish collections (2018–2019) in tributaries of the Eleven Point River basin in Arkansas to examine patterns of fish assemblage change. Fish assemblage change variables were compared to pasture land use/land cover (LULC) at multiple scales and in-stream habitat variables to understand relationships and discover potential correlates suggesting biotic homogenization. Fish assemblages in the Eleven Point River basin of Arkansas have experienced significant spatiotemporal changes, and LULC change and habitat alterations may have influenced this process. Increased tolerant species and decreased intolerant species at sites contributed to biotic homogenization, particularly in pool habitats. Surprisingly, expansion of some intolerant fishes was also observed that tend to occupy riffles. Sites with high percentages of pasture LULC at finer spatial scales typically had more homogenised fish assemblages. We hypothesized gravel aggradation from local pasture land use has degraded pools and increased riffle habitat, resulting in homogenised fish assemblages in the Eleven Point River basin over the study period. Few studies link LULC, in-stream habitat, and biotic homogenization when examining fish assemblage change over time, and these dynamics can be particularly complex in upland streams experiencing gravel aggradation. Similar research in other upland, gravel-bed river systems would provide a broad understanding of the presented environmental associations.