Search for: All records

A fundamental goal of ecology is to understand how the physical environment influences intraspecific variability in life history and, consequently, fitness. In streams, discharge and associated habitat conditions change along a continuum from intermittency to permanence: Headwater streams typically have smaller watersheds and are thus more prone to drying than higher‐order streams with larger watersheds and more consistent discharge. However, few empirical studies have assessed life history and associated population responses to this continuum in aquatic organisms. We tested the prediction that individual growth, rate of development, and population growth increase with watershed area in the long‐lived stream salamanderGyrinophilus porphyriticus, where we use watershed area as a proxy for hydrologic intermittence. To address this hypothesis, we used 8 years of mark–recapture data from 53 reaches across 10 headwater streams in New Hampshire, USA. Individual growth rates and mean size at metamorphosis increased with watershed area for watersheds from 0.12 to 1.66 km². Population growth rates increased with watershed area; however, this result was not statistically significant at our sample size. Mean age of metamorphosis did not vary across watershed areas. Lower individual growth rates and smaller sizes at metamorphosis likely contributed to reduced lifetime fecundity and population growth in reaches with the smallest watershed areas and highest vulnerability to drought. These responses suggest that as droughts increase due to climate change, headwater specialists in hydrologically intermittent environments will experience a reduction in fitness due to smaller body sizes or other growth‐related mechanisms.

 

This data set includes spatially explicit mark-recapture data of the Northern Spring Salamander (Gyrinophilus porphyriticus) collected via telemetry during the summer months (June – September) from 2019 - 2021 from eight reaches in multiple streams in the Hubbard Brook Experimental Forest. Salamanders were captured by hand and marked with PIT-tags. Telemetry surveys occurred weekly. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. These data are being used to publish the following papers: Cochrane, M. M., B. R. Addis, L. K. Swartz, and W. H. Lowe. 2023. Individual and population growth rates decline with watershed area in a stream salamander. In review Ecology. Cochrane, M. M., and W. H. Lowe. 2023. Floods increase downstream movement of adult and larval life stages of a headwater stream salamander. In prep Freshwater Biology. 

This dataset includes spatially explicit mark-recapture data of the Northern Spring Salamander (Gyrinophilus porphyriticus) collected during the summer months (June – August) from downstream and upstream reaches in multiple streams in the Hubbard Brook Experimental Forest. Downstream reaches begin at the confluence with the Main Hubbard and extend upstream 500 meters and upstream reaches begin at the weir and extend downstream 500 meters. Downstream reaches contain brook trout and upstream reaches do not. We used a robust design framework with 9 surveys per reach each summer (3 primary occasions with 3 secondary occasions each). Salamanders were captured by hand and marked with either Visual Implant Elastomer and/or a PIT tag. The data table herein is specific to the following publication: Lowe, W.H., B.R. Addis, M.M. Cochrane, and L.K. Swartz. In press. Source-sink dynamics within a complex life history. Ecology. These data are a subset of the primary long term dataset available at https://doi.org/10.6073/pasta/cd5f5a03df194930bf87eb12157b8182 These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

This data set includes spatially explicit mark-recapture data of the Northern Spring Salamander (Gyrinophilus porphyriticus) collected during the summer months (June – August) from downstream and upstream reaches in multiple streams in the Hubbard Brook Experimental Forest. Downstream reaches begin at the confluence with the Main Hubbard and extend upstream 500 meters and upstream reaches begin at the weir and extend downstream 500 meters. Downstream reaches contain brook trout and upstream reaches do not. We used a robust design framework with approximately 9 surveys per reach each summer (3 primary occasions with 3 secondary occasions each). Salamanders were captured by hand and marked with either Visual Implant Elastomer and/or a PIT tag. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. These data have been published in the following papers: Lowe WH, Addis BR, Smith MR, Davenport JM. The spatial structure of variation in salamander survival, body condition and morphology in a headwater stream network. Freshwater Biol. 2018;63:1287–1299. https://doi.org/10.1111/fwb.13133 Lowe, W. H., and Addis, B. R.. 2019. Matching habitat choice and plasticity contribute to phenotype–environment covariation in a stream salamander. Ecology 100( 5):e02661. 10.1002/ecy.2661 Lowe, W.H., et al. Hydrologic variability contributes to reduced survival through metamorphosis in a stream salamander. Proceedings of the National Academy of Sciences 2019; 116.39: 19563-19570. Bryant, A.R., Gabor, C.R., Swartz, L.K., Wagner, R., Cochrane, M.M., Lowe, W.H. Differences in corticosterone release rates of larval Spring Salamanders (Gyrinophilus porphyriticus) in response to native fish presence. Biology 2022; 11.484. https://doi.org/10.3390/biology11040484 Addis, B.R., and W.H. Lowe. Environmentally associated variation in dispersal distance affects inbreeding risk in a stream salamander." The American Naturalist 2022. 

Invasive fish predators are an important factor causing amphibian declines and may have direct and indirect effects on amphibian survival. For example, early non-lethal exposure to these stressors may reduce survival in later life stages, especially in biphasic species. In amphibians, the glucocorticoid hormone corticosterone is released by the hypothalamo–pituitary–interrenal axis (HPI), as an adaptive physiological response to environmental stressors. The corticosterone response (baseline and response to acute stressors) is highly flexible and context dependent, and this variation can allow individuals to alter their phenotype and behavior with environmental changes, ultimately increasing survival. We sampled larvae of the spring salamander (Gyrinophilus porphyriticus) from two streams that each contained predatory brook trout (Slavelinus fontinalis) in the lower reaches and no predatory brook trout in the upper reaches. We measured baseline and stress-induced corticosterone release rates of larvae from the lower and upper reaches using a non-invasive water-borne hormone assay. We hypothesized that corticosterone release rates would differ between larvae from fish-present reaches and larvae from fish-free reaches. We found that baseline and stressor-induced corticosterone release rates were downregulated in larvae from reaches with fish predators. These results indicate that individuals from reaches with predatory trout are responding to fish predators by downregulating corticosterone while maintaining an active HPI axis. This may allow larvae more time to grow before metamorphosing, while also allowing them to physiologically respond to novel stressors. However, prolonged downregulation of corticosterone release rates can impact growth in post-metamorphic individuals. 

Source–sink patch dynamics occur when movement from sources stabilizes sinks by compensating for low local vital rates. The mechanisms underlying source–sink dynamics may be complicated in species that undergo transitions between discrete life stages, particularly when stages have overlapping habitat requirements and similar movement abilities. In these species, for example, the demographic effects of movement by one stage may augment or offset the effects of movement by another stage. We used a stream salamander system to investigate patch dynamics within this form of complex life history. Specifically, we tested the hypothesis that the salamanderGyrinophilus porphyriticusexperiences source–sink dynamics in riffles and pools, the dominant geomorphic patch types in headwater streams. We estimated stage‐specific survival probabilities in riffles and pools and stage‐specific movement probabilities between the two patch types using 8 years of capture–recapture data on 4491 individuals, including premetamorphic larvae and postmetamorphic adults. We then incorporated survival and movement probabilities into a stage‐structured, two‐patch model to determine the demographic interactions between riffles and pools. Monthly survival probabilities of both stages were higher in pools than in riffles. Larvae were more likely to move from riffles to pools, but adults were more likely to move from pools to riffles, despite experiencing much lower survival in riffles. In simulations, eliminating interpatch movements by both stages indicated that riffles are sinks that rely on immigration from pools for stability. Allowing only larvae to move stabilized both patch types, but allowing only adults to move destabilized pools due to the demographic cost of adult emigration. These results indicated that larval movement not only stabilizes riffles, but also offsets the destabilizing effects of maladaptive adult movement. Similar patch dynamics may emerge in any structured population in which movement and local vital rates differ by age, size, or stage. Addressing these forms of internal demographic structure in patch dynamics analyses will help to refine and advance general understanding of spatial ecology.