Temperature‐dependent competition between juvenile salmonids in small streams

Abstract

Biotic interactions affect species distributions, and environmental factors that influence these interactions can play a key role when range shifts in response to environmental change are modelled. In a field experiment using enclosures, we studied the effects of the thermal habitat on intra‐ versus inter‐specific competition of juvenile Dolly Varden Salvelinus malma and white‐spotted charr Salvelinus leucomaenis, as measured by differences in specific growth rates during summer in allopatric and sympatric treatments. Previous laboratory experiments have shown mixed results regarding the importance of temperature‐dependent competitive abilities as a main driver for spatial segregation in stream fishes, and no study so far has confirmed its existence in natural streams. Under natural conditions in areas where the two species occur in sympatry, Dolly Varden dominate spring‐fed tributaries (cold, stable thermal regime), whereas both species often coexist in non‐spring‐fed tributaries (warm, unstable thermal regime). Enclosures (charr density = 6 per m2) were placed in non‐spring‐fed (10–14°C) and spring‐fed (7–8°C) tributaries. In enclosures placed in non‐spring‐fed tributaries, Dolly Varden grew 0.81% per day in allopatry and had negative growth (−0.33% per day) in sympatry, whereas growth rates were similar in allopatry and sympatry in spring‐fed tributaries (0.68 and 0.58% per day). White‐spotted charr grew better in sympatry than in allopatry in both thermal habitats. In non‐spring‐fed tributaries, they grew 0.17 and 0.79% per day and in spring‐fed tributaries 0.46 and 0.75% per day in allopatry and sympatry, respectively. The negative effect of inter‐specific competition from white‐spotted charr on Dolly Varden thus depended on the thermal habitat. However, there was no strong evidence of a temperature‐dependent effect of intra‐ and inter‐specific competition on white‐spotted charr growth. Multiple factors may shape species distribution patterns, and we show that temperature may mediate competitive outcomes and thus coexistence in stream fish. These effects of temperature will be important to incorporate into mechanistic and dynamic species distribution models.

Effects of Warming on Intraguild Predator Communities with Ontogenetic Diet Shifts

“…a juvenile bottleneck). Myrvold and Kennedy (2015) showed empirically that warming increases intraspecific competition and causes juvenile bottlenecks in their study of wild steelhead, and Watz et al (2019) found support for temperature effects on growth via interspecific competition in two species of charr. However, to our knowledge, no studies have until now linked juvenile bottlenecks to temperature-dependent predation and interspecific competition, and the resulting effects of warming on the composition of intraguild predation communities.…”

Physiological basis of interactive responses to temperature and salinity in coastal marine invertebrate: Implications for responses to warming

“…Responses to temperature and salinity are likely to define components of performance that are relevant for, for example, competition and larval transport. For instance, competitive abilities can change according to the temperature where such competition occurs (Tomanek & Helmuth, 2002;Watz et al, 2019); comparative studies should provide insights into how the outcome of competition is modulated by responses to combination of temperature and salinity. In addition, larval transport in many crustaceans depends on circatidal or diel migration behavior, which should be driven by the capacity of larvae to accumulate and use energy for vertical swimming.…”

Asymmetric competition over space use and territory between native brown trout (Salmo trutta) and invasive brook trout (Salvelinus fontinalis)

“…As such, the stronger avoidance response of the smaller 0+ brown trout could indicate that they were more susceptible to predation than the larger 0+ brook trout due to gape limitations of the 1+ individuals (Keeley & Grant, 2001). With the multitude of cues present in a stream, it is unlikely that there is only one factor that determines the spatial distribution of individuals, rather it may be a combination of visual and chemical cues (Brown, 2003;Höjesjö et al, 2015), presence of predators (Ferrari et al, 2010) and habitat variability (Höjesjö et al, 2004;Watz et al, 2019) that helps form hierarchies and spatial distribution of individuals (Kaspersson & Höjesjö, 2009;Nakano, 1995). The results from the territorial contest after manipulating residence duration was rather surprising as only one brown trout won the territorial contest.…”