Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

<em>Abstract</em>.—Using artificial stream mesocosms, we conducted two experiments in consecutive summers to examine proximate and residual effects of simulated drought on survivorship, body size, condition, and reproduction of fishes common in southern Oklahoma streams. In summer 2000, we examined proximate effects on central stonerollers <em>Campostoma anomalum</em>, bigeye shiners <em>Notropis boops</em>, black-stripe topminnow <em>Fundulus notatus</em>, longear sunfish <em>Lepomis megalotis</em>, and orange-throat darters <em>Etheostoma spectabile </em>exposed to either continuous flow or to simulated drought for 40 d. Survivorship did not differ between treatments for central stonerollers, bigeye shiners, or orangethroat darters, but was lower in the drought treatment for both blackstripe topminnow and longear sunfish. Body size of survivors in the drought treatment tended to be smaller for central stonerollers. Condition of bigeye shiner and central stoneroller individuals was lower in the drought treatment, and bigeye shiner females exposed to drought were less likely to have mature eggs. In summer 2001, we simulated drought for 35 d and examined residual effects on central stonerollers, bigeye shiners, and orangethroat darters approximately 6 months later. Survivorship assayed in spring 2002 was marginally lower for orangethroat darters. Body size of central stonerollers in the drought treatment was smaller, consistent with proximate effects of drought on body size. Bigeye shiners did not differ between treatments in either body size or condition, indicating no residual effect of drought on fat stores despite much lower condition immediately following drought in summer 2000. For orangethroat darters, individuals exposed to drought tended to be larger and in better condition and to have more mature gonads than individuals in the flow treatment after the recovery period. The results of our two experiments demonstrate that drought affects survival, growth, body condition, and reproduction in different ways for different species, and proximate effects do not necessarily predict residual effects on fishes that survive drought.

River Otter, Lontra canadensis, Food Habits in the Missouri Ozarks

The reintroduction of River Otters (Lontra canadensis) between 1982 and 1992 resulted in widespread occurrence of the species throughout the Missouri Ozarks. This study examined otter diets from the vicinity of two Ozark streams in relation to seasonal and spatial trends. Otter scats (N = 4750) were collected and analyzed from the Osage Fork River and Big Piney River during the summer and winter seasons of 2001 and 2002. During the winter (January-March), fish occurred in 86% of the samples. During the summer (June–August), occurrence of fish dropped to approximately 15% for both rivers. Seven families of fish were identified in the diets, with Centrarchidae being most common regardless of river or season. Within the Centrarchidae, the genus Lepomis (mostly Longear Sunfish, Lepomis megalotis) was most common, with Micropterus (mostly Smallmouth Bass, Micropterus dolomieu) and Rock Bass (Ambloplites rupestris) also well represented. The mean age of Ambloplites consumed (mean = 3.3 years) was consistently older than that of either Micropterus (mean = 2.54 years) or Lepomis (mean = 2.78 years). Crayfish were recovered from a mean of 85.2% of scats in the winter and 99% in the summer. Smaller fish and crayfish were more common from the upper reaches of the streams while larger fish were prevalent in the lower reaches.

Genetic variation in the longear sunfish (Lepomis megalotis)

The systematics and zoogeography of the longear sunfish (Lepomis megalotis) are poorly understood. Relationships among geographic variants throughout the range of the species are unclear, and it is uncertain whether the northern longear sunfish, L. m. peltastes, should be classified as a separate species. We used protein electrophoresis to examine genetic variation among 22 longear sunfish populations and one dollar sunfish (Lepomis marginatus) population. Principal component analysis of allele frequency data could not separate the most morphologically distinct form, the northern longear sunfish, from the central long-ear sunfish, L. m. megalotis. Populations distributed from the Missouri River basin to the Colorado River in Texas, for which the subspecific names L. m. breviceps and L. m. aquilensis are available, clustered as a distinct group. No evidence was found to suggest that a distinct form exists in the Ozark Highlands. Lepomis marginatus was genetically distinct from all L. megalotis populations, but most distinct from L. m. megalotis and L. m. peltastes. Protein electrophoresis should allow diagnosis of distribution limits and intergrade zones of southwestern forms, but a more sensitive technique is required to separate L. m. megalotis and L. m. peltastes.