Browsing by Author "Daniels, Melinda D."

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Crayfish ecosystem engineering effects on riverbed disturbance and topography are mediated by size and behavior
(2018-12) Albertson, Lindsey K.; Daniels, Melinda D.
Animals that burrow, forage, or produce physical structures can have substantial impacts on transport processes related to erosion. However, the influence of behavior and body size on regulating the magnitude of engineering effects by animals is not well understood. For example, crayfish are common and abundant freshwater organisms that disturb sediments in ways that influence gravel transport, fine sediment suspension, and bank stability. Animals such as crayfish also display complex territorial and aggressive behaviors, often related to body size, which might influence their ability to influence sediment transport dynamics. We conducted an experiment with spiny-cheek crayfish (Faxonius limosus) to investigate the influence of behavior and body size on substrate disturbance. The experiment included 4 enclosure (0.31-m long x 0.21-m wide x 0.17-m deep) treatments that differed in the body size of individual crayfish and the amount of biomass: 1) 2 small young-of-the-year (YOY) crayfish of 15-mm carapace length (CL) (abbreviated SS), 2) 2 larger, 1 + y-old crayfish of 25-mm CL (abbreviated LL), 3) 1 crayfish of 15- and one crayfish of 25-mm CL (abbreviated SL), and 4) a control with no crayfish. We monitored construction of pits within the gravel bed and the proportion of streambed over which crayfish exhumed subsurface gravels. We also used videography to quantify aggressive encounters between crayfish individuals. We found that body size strongly influenced the amount and type of disturbance, with large crayfish creating a significantly greater number of pit structures than small crayfish. Additionally, surface gravels were moved over 11.4, 9.3, 1.3, and 0.003% of the bed surface area in LL, SL, SS, and control treatments, respectively. On average, 77% of interactions between crayfish individuals were aggressive regardless of size, which may explain why the amount of change in bed topography in the LL treatments did not always exceed that in the SL treatments. Successfully incorporating animal behavior into sediment transport models may require consideration of both behavior and body size.
Facilitation strength across environmental and beneficiary trait gradients in stream communities
(Wiley, 2023-08) Tumolo, Benjamin B.; Albertson, Lindsey K.; Daniels, Melinda D.; Cross, Wyatt F.; Sklar, Leonard L.
Ecosystem engineers modify habitats in ways that facilitate other community members by ameliorating harsh conditions. The strength of such facilitation is predicted to be influenced by both beneficiary traits and abiotic context. One key trait of animals that could control the strength of facilitation is beneficiary body size because it should determine how beneficiaries fit within and exploit stress ameliorating habitat modifications. However, few studies have measured how beneficiary body size relates to facilitation strength along environmental gradients. We examined how the strength of facilitation by net‐spinning caddisflies on invertebrate communities in streams varied along an elevation gradient and based on traits of the invertebrate beneficiaries. We measured whether use of silk retreats as habitat concentrated invertebrate density and biomass compared to surrounding rock surface habitat and whether the use of retreat habitat varied across body sizes of community members along the gradient. We found that retreats substantially concentrated the densities of a diversity of taxa including eight different Orders, and this effect was greatest at high elevations. Caddisfly retreats also concentrated invertebrate biomass more as elevation increased. Body size of invertebrates inhabiting retreats was lower than that of surrounding rock habitats at low elevation sites, however, body size between retreats and rocks converged at higher elevation sites. Additionally, the body size of invertebrates found in retreats varied within and across taxa. Specifically, caddisfly retreats functioned as a potential nursery for taxa with large maximal body sizes. However, the patterns of this taxon‐specific nursery effect were not influenced by elevation unlike the patterns observed based on community‐level body size. Collectively, our results indicate that invertebrates use retreats in earlier life stages or when they are smaller in body size independent of life stage. Furthermore, our analysis suggests that facilitation strength intensifies as elevation increases within stream invertebrate communities. Further consideration of how trait variation and environmental gradients interact to determine the strength and direction of biotic interactions will be important as species ranges and environmental conditions continue to shift.
Occupied and abandoned structures from ecosystem engineering differentially facilitate stream community colonization
(2019-05) Tumolo, Benjamin B.; Albertson, Lindsey K.; Cross, Wyatt F.; Daniels, Melinda D.; Sklar, Leonard S.
Ecosystem engineers transform habitats in ways that facilitate a diversity of species; however, few investigations have isolated short‐term effects of engineers from the longer‐term legacy effects of their engineered structures. We investigated how initial presence of net‐spinning caddisflies (Hydropsychidae) and their structures that provide and modify habitat differentially influence benthic community colonization in a headwater stream by conducting an in situ experiment that included three treatments: (1) initial engineering organism with its habitat modification structure occupied (hereafter caddisfly); (2) initial habitat modification structure alone (hereafter silk); and (3) a control with the initial absence of both engineer and habitat modification structure (hereafter control). Total invertebrate colonization density and biomass was higher in caddisfly and silk treatments compared to controls (~25% and 35%, respectively). However, finer‐scale patterns of taxonomy revealed that density for one of the taxa, Chironomidae, was ~19% higher in caddisfly compared to silk treatments. Additionally, conspecific biomass was higher by an average of 50% in silk treatments compared to controls; however, no differences in Hydropsyche sp. biomass were detected between caddisfly treatments and controls, indicating initially abandoned silk structures elevated conspecific biomass. These findings suggest that the positive effects of the habitat modification structures that were occupied for the entirety of the experiment may outweigh any potential negative impacts from the engineer, which is known to be territorial. Importantly, these results reveal that the initial presence of the engineer itself may be important in maintaining the ecological significance of habitat modifications. Furthermore, the habitat modifications that were initially abandoned (silk) had similar positive effects on conspecific biomass compared to caddisfly treatments, suggesting legacy effects of these engineering structures may have pertinent intraspecific feedbacks of the same magnitude to that of occupied habitat modifications. Elucidating how engineers and their habitat modifications differentially facilitate organisms will allow for a clearer mechanistic understanding of the extent to which animal engineers and their actions influence aspects of community organization such as colonization.