The evolution and maintenance of secondary sexual characteristics and behavior are heavily influenced by the variance in mating success among individuals in a population. The operational sex ratio ...(OSR) is often used as a predictor of the intensity of competition for mates, as it describes the relative number of males and females who are ready to mate. We investigate changes in aggression, courtship, mate guarding, and sperm release as a function of changes in the OSR using meta-analytic techniques. As the OSR becomes increasingly biased, aggression increases as competitors attempt to defend mates, but this aggression begins to decrease at an OSR of 1.99, presumably due to the increased costs of competition as rivals become more numerous. Sperm release follows a similar but not significant trend. By contrast, courtship rate decreases as the OSR becomes increasingly biased, whereas mate guarding and copulation duration increase. Overall, predictable behavioral changes occur in response to OSR, although the nature of the change is dependent on the type of mating behavior. These results suggest considerable flexibility of mating system structure within species, which can be predicted by OSR and likely results in variation in the strength of sexual selection.
In an attempt to restore the connectivity of fragmented river habitats, a variety of passage facilities have been installed at river barriers. Despite the cost of building these structures, there has ...been no quantitative evaluation of their overall success at restoring fish passage. We reviewed articles from 1960 to 2011, extracted data from 65 papers on fish passage efficiency, size and species of fish, and fishway characteristics to determine the best predictors of fishway efficiency. Because data were scarce for fishes other than salmonids (order Salmoniformes), we combined data for all non‐salmonids for our analysis. On average, downstream passage efficiency was 68.5%, slightly higher than upstream passage efficiency of 41.7%, and neither differed across the geographical regions of study. Salmonids were more successful than non‐salmonids in passing upstream (61.7 vs. 21.1%) and downstream (74.6 vs. 39.6%) through fish passage facilities. Passage efficiency differed significantly between types of fishways; pool and weir, pool and slot and natural fishways had the highest efficiencies, whereas Denil and fish locks/elevators had the lowest. Upstream passage efficiency decreased significantly with fishway slope, but increased with fishway length, and water velocity. An information‐theoretic analysis indicated that the best predictors of fish passage efficiency were order of fish (i.e. salmonids > non‐salmonids), type of fishway and length of fishway. Overall, the low efficiency of passage facilities indicated that most need to be improved to sufficiently mitigate habitat fragmentation for the complete fish community across a range of environmental conditions.
Competition from non-native salmonids is potentially impairing efforts to restore Atlantic salmon (Salmo salar) to parts of their historical range. In three separate meta-analyses, we collected 104 ...effect sizes from 25 published papers to quantify the effect of both native and non-native salmonids on the performance (i.e., behaviour, habitat use, growth and survival) of Atlantic salmon. The presence of other species had negative effects on the performance of Atlantic salmon; in particular, non-native species and brown trout (Salmo trutta), whether native or non-native, had the most negative effects. Contrary to our predictions, the negative effects of other species were not exacerbated in laboratory compared to field studies and did not increase with total salmonid abundance or the relative body size of the competitors. However, most studies in our analyses were conducted under laboratory conditions and at densities much higher than found in nature. Thus, a realistic assessment of the potential success of restoration programs when interspecific competitors are present should include more studies conducted under natural conditions.
Habitat degradation is one of the major reasons for freshwater species decline. Hydrogeomorphological processes (such as sediment transport, bank erosion, and flooding) operate at the catchment scale ...and determine habitat features in river reaches. However, habitat quality indices and restoration for freshwater fish species are often implemented at small spatial scales of a few hundred metres. The Morphological Quality Index (MQI) considers fluvial processes at larger scales as well as channel forms, human impacts, and historical changes, but few studies have assessed its relevance for ecosystem health. We investigated relationships between the MQI, habitat quality (using the Qualitative Habitat Evaluation Index, QHEI), land cover, and fish metrics (number of fish species, index of biotic integrity (IBI), and trout biomass) in 26 salmonid streams in Aotearoa New Zealand and Southern Ontario, Canada. We found a significant correlation between the MQI and QHEI, and both metrics were correlated with urban and native forest proportion in the catchment. However, we found no relation between the MQI and the proportion of agricultural land in the catchment, while the QHEI was correlated with agricultural land in the riparian zone, highlighting the importance of vegetated riparian buffers in providing fish habitat. Establishing a strong correlation with fish metrics remains challenging. Nevertheless, a modified MQI targeting ecological health could be used as an effective management tool for aquatic conservation.
Owing to declines in salmonid populations, in-stream restoration structures have been used for over 80 years to increase abundance of fish. However, the relative effectiveness of these structures ...remains unclear for some species or regions, partly due to contrasting conclusions from two previous meta-analyses. To update and reconcile these previous analyses, we conducted a meta-analysis using data available from 1969 to 2019 to estimate the effect of in-stream structures on salmonid abundance (number and density) and biomass. Data from 100 stream restoration projects showed a significant increase in salmonid abundance (effect size 0.636) and biomass (0.621), consistent with previous reviews and studies, and a stronger effect was found in adults than in juvenile fish. Despite a shift towards using more natural structures (wood and boulders) since the 1990s, structures have not become more effective. However, most projects monitor for less than 5 years, which may be insufficient time in some systems for channel morphology to adjust and population changes to be apparent. Process-based techniques, which give more space for the river, allow more long-term, self-sustaining restoration.
Despite the widespread use of stream restoration structures to improve fish habitat, few quantitative studies have evaluated their effectiveness. This study uses a meta-analysis approach to test the ...effectiveness of five types of in-stream restoration structures (weirs, deflectors, cover structures, boulder placement, and large woody debris) on both salmonid abundance and physical habitat characteristics. Compilation of data from 211 stream restoration projects showed a significant increase in pool area, average depth, large woody debris, and percent cover, as well as a decrease in riffle area, following the installation of in-stream structures. There was also a significant increase in salmonid density (mean effect size of 0.51, or 167%) and biomass (mean effect size of 0.48, or 162%) following the installation of structures. Large differences were observed between species, with rainbow trout (
Oncorhynchus mykiss
) showing the largest increases in density and biomass. This compilation highlights the potential of in-stream structures to create better habitat for and increase the abundance of salmonids, but the scarcity of long-term monitoring of the effectiveness of in-stream structures is problematic.
Understanding the complex variation in patterns of density‐dependent individual growth and survival across populations is critical to adaptive fisheries management, but the extent to which this ...variation is caused by biological or methodological differences is unclear. Consequently, we conducted a correlational meta‐analysis of published literature to investigate the relative importance of methodological and biological predictors on the shape and strength of density‐dependent individual growth and survival in salmonids. We obtained 160 effect sizes from 75 studies of 12 species conducted between 1977 and 2019 that differed in experimental approach (sensu Ecological Monographs, 54, 187–211; 65 laboratory experiments, 60 observational field studies, and 35 field experiments). The experimental approach was the strongest factor influencing the strength of density dependence across studies: density‐dependent survival was stronger than growth in field observational studies, whereas laboratory experiments detected stronger density‐dependent growth than survival. The difference between density‐dependent growth and survival was minimal in field experiments, and between lotic and lentic habitats. The shape of density dependence (logarithmic, linear, exponential or density‐independent) could be predicted with 66.7% accuracy based solely on the experimental approach and the density gradient (highest/lowest*100) of the study. Overall, the strength and shape of density dependence were primarily influenced by methodological predictors, while biological factors (predator presence, food abundance, and species) had predictable but modest effects. For both empirical studies and adaptive fisheries management, we recommend using field experiments with a density gradient of at least 470% to detect the proper shape of the density‐dependent response, or accounting for potential biases if observational or laboratory studies are conducted.
The restricted movement paradigm (RMP) asserts that stream fishes are sedentary, living much of their lives within a single reach. To test the RMP, we implanted eyed Atlantic salmon eggs (Salmo ...salar) into a total of 19 artificial redds, in seven salmon-free streams, in 6 years, and estimated summer fry dispersal through electrofishing surveys. As expected, most fry dispersed downstream, but an average of 35% moved upstream. Surprisingly, fry moved just as far upstream as downstream (medians = 403 and 404 m, respectively). Fry were larger at lower densities and farther from redd sites, consistent with density-dependent growth, and larger upstream than downstream, possibly indicating that larger fry were better able to move upstream against the current. Dispersal distances were normally distributed around all but two of 19 redds, and half of the downstream dispersal curves were best described by unimodal distributions, consistent with a homogeneous movement strategy. Our data suggest that salmon fry were more mobile and move upstream more than previously thought, which should facilitate their stocking or reintroduction to new habitats.
Sustainable management of exploited populations benefits from integrating demographic and genetic considerations into assessments, as both play a role in determining harvest yields and population ...persistence. This is especially important in populations subject to size‐selective harvest, because size selective harvesting has the potential to result in significant demographic, life‐history, and genetic changes. We investigated harvest‐induced changes in the effective number of breeders (N̂b) for introduced brook trout populations (Salvelinus fontinalis) in alpine lakes from western Canada. Three populations were subject to 3 years of size‐selective harvesting, while three control populations experienced no harvest. The N̂c decreased consistently across all harvested populations (on average 60.8%) but fluctuated in control populations. There were no consistent changes in N̂b between control or harvest populations, but one harvest population experienced a decrease in N̂b of 63.2%. The N̂b/N̂c ratio increased consistently across harvest lakes; however we found no evidence of genetic compensation (where variance in reproductive success decreases at lower abundance) based on changes in family evenness (FÊ) and the number of full‐sibling families (N̂fam). We found no relationship between FÊ and N̂c or between N̂fam/N̂c and FÊ. We posit that change in N̂b was buffered by constraints on breeding habitat prior to harvest, such that the same number of breeding sites were occupied before and after harvest. These results suggest that effective size in harvested populations may be resilient to considerable changes in Nc in the short‐term, but it is still important to monitor exploited populations to assess the risk of inbreeding and ensure their long‐term survival.
Abstract
Augmenting habitat complexity by adding structure has been used to increase the population density of some territorial species in the wild and to reduce aggression among captive animals. ...However, it is unknown if all territorial species are affected similarly by habitat complexity, and whether these effects extend to non-territorial species. We conducted a meta-analysis to compare the behavior of a wide range of territorial and non-territorial taxa in complex and open habitats to determine the effects of habitat complexity on 1) territory size, 2) population density, 3) rate and time spent on aggression, 4) rate and time devoted to foraging, 5) rate and time spent being active, 6) shyness/boldness, 7) survival rate, and 8) exploratory behavior. Overall, all measures were significantly affected by habitat complexity, but the responses of territorial and non-territorial species differed. As predicted, territorial species were less aggressive, had smaller territories and higher densities in complex habitats, whereas non-territorial species were more aggressive and did not differ in population density. Territorial species were bolder but not more active in complex habitats, whereas non-territorial species were more active but not bolder. Although the survival of non-territorial species increased in complex habitats, no such increase was observed for territorial species. The increased safety from predators provided by complex habitats may have been balanced by the higher population densities and bolder behavior in territorial species. Our analysis suggests that territorial and non-territorial animals respond differently to habitat complexity, perhaps due to the strong reliance on visual cues by territorial animals.
The behavioural response to habitat complexity differs for territorial and non-territorial animals. Territorial species are less aggressive, have smaller territories and are more abundant, while non-territorial species show higher activity and more aggression in response to habitat complexity. Additionally, the expected decrease in predation risk in complex habitats was observed for non-territorial animals but not for territorial animals.
PDF
