Ecological marginality and recruitment loss in the globally endangered freshwater pearl mussel

Abstract

Aim Ecological marginality is the existence of species/populations in the margins of their ecological niche, where conditions are harsher, and the risk of extinction is more pronounced. In threatened long‐lived species, the disparity between distribution and population demography may provide understanding of how environmental heterogeneity shapes ecological marginality, potential extinction patterns and range shifts. We set out to evaluate this by combining a species distribution model (SDM) with population‐specific demography data. Location Sweden, 450,000 km2. Major Taxa Studied Freshwater pearl mussel (FPM, Margaritifera margaritifera) and two salmonid fish species. Methods A SDM for the mussel was constructed with MaxEnt using salmonid host fish (Salmo trutta plus S. salar) density, extreme low and high temperatures, precipitation, altitude, and clay content as explanatory variables. The output was used to test the ecological marginality hypothesis by evaluating whether lowly predicted populations had higher loss of recruitment. Logistic regression was used to explicitly test the factors involved in recruitment loss. Results Host fish density contributed the most (50.3%) to the mussel distribution, followed by lowest temperature the coldest month (34.3%) and altitude (10.3%), while the remaining explanatory variables contributed minimally (<3.3%). Populations with lower SDM scores lacked recruitment to a significantly higher degree. Populations inhabiting areas at low altitude, with lower densities of host fish, and warmer winter temperatures have lost recruitment to a higher degree. Main Conclusions We found support for the ecological marginality hypothesis. The patterns indicate that FPM habitat niche may shift northwards over time. Salmonid host fish density seems to be a driving factor for both historical distribution and recent demographic performance. Finally, we emphasize the value of combining SDMs with independent data on population demography as it both lends rigidity to model validation and understanding of how ecological marginality affects species distribution and viability.

Growth pattern and the condition index of nomei fish Harpodon nehereus captured with mini-trawl in Tarakan Waters

“…The various condition index values depend on the diet, age, sex and gonad maturity. In addition, the condition factor can go up and down because it is dependent on the spawning season for fish, especially female fish [23]; [26]. The growth pattern based on the length weight relationship for male and female H. nehereus was allometric negative the gain of weight is slower than the gain of length.…”

Niche position and niche breadth effects on population abundances: A case study of New World Warblers (Parulidae)

“…For instance, populations of Freshwater pearl mussels residing in suboptimal environments rarely experience recruitment. This implies a higher potential risk of extinction for these populations (Tamario et al., 2022 ). The ability of species to occupy the most available environments, particularly those near the most common environments (referred to as NP), has been a key factor in explaining the abundance and occupancy patterns of bromeliad invertebrates at a large spatial scale (Marino et al., 2020 ).…”