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A central aim of ecology is to explain the heterogeneous distribution of biodiversity on earth. As expectations of diversity loss grow, this understanding is also critical for effective management and conservation. Although explanations for biodiversity patterns are still a matter for intense debate, they have often been considered to be scale-dependent. At large geographical scales, biogeographers have suggested that variation in species richness results from factors such as area, temperature, environmental stability, and geological processes, among many others. From the species pools generated by these large-scale processes, community ecologists have suggested that local-scale assembly of communities is achieved through processes such as competition, predation, recruitment, disturbances and immigration. Here we analyse hypotheses on speciation and dispersal for reef fish from the Indian and Pacific oceans and show how dispersal from a major centre of origination can simultaneously account for both large-scale gradients in species richness and the structure of local communities.

Abstract. Four early life events (i.e., hatching, the ontogenetic diet shift to piscivory, fall lipid accumulation, and the first winter) are conceptualized as being critical to 1st-yr recruitment success of largemouth bass (Micropterus salmoides) via cause-and-effect associations among them. Toward this end, we conducted a multiple life-stage investigation of largemouth bass to examine the functional dependency and significance to recruitment of these temporally separated early life events. Specifically, we quantified growth and survival of two largemouth bass year-classes in six Alabama ponds from hatching to the end of the first winter.The first winter was an important survival bottleneck with lower largemouth bass survival in ponds with smaller largemouth bass (high-density ponds), relative to ponds with larger fish (low-density ponds). While cannibalism was not important, we found sizedependent first-winter mortality to be regulated directly by lipid reserves (i.e., triglycerides) accumulated during fall, and indirectly by both hatch date and the ontogenetic diet shift to piscivory during summer. Early-hatched largemouth bass attained an initial length advantage, remaining large relative to late-hatched fish, despite the relatively higher growth rate of late-hatched fish during their first month of life. Enhanced size permitted earlyhatched fish to become piscivorous before late-hatched fish, increasing their access to fish prey (i.e., sunfishes) during fall. This in turn elevated their fall lipid accumulation and winter survival above that of late-hatched fish. Our results indeed suggest that 1st-yr recruitment of largemouth bass in southern systems is governed by several functionally dependent critical events. Because each is likely vital to understanding recruitment variability, we suggest that future recruitment studies should adopt a more synthetic (i.e., multiple life-stage) approach.

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Although climate warming is expected to benefit temperate ectotherms by lengthening the summer growing season, declines in reproductive success following short, warm winters may counter such positive effects. Here we present long-term (1973–2010) field patterns for Lake Erie yellow perch, Perca flavescens, which show that failed annual recruitment events followed short, warm winters. Subsequent laboratory experimentation and field investigations revealed how reduced reproductive success following short, warm winters underlie these observed field patterns. Following short winters, females spawn at warmer temperatures and produce smaller eggs that both hatch at lower rates and produce smaller larvae than females exposed to long winters. Our research suggests that continued climate warming can lead to unanticipated, negative effects on temperate fish populations.

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Similar to coastal marine systems, Lake Erie exhibits open-water river plumes that differ physicochemically and biologically from surrounding waters. To explore their importance to yellow perch ( Perca flavescens ) recruitment in western Lake Erie, we tested two related hypotheses: (i) contributions of larvae to the juvenile stage (when recruitment is set) would be greater from nutrient-rich Maumee River plume (MRP) waters than from less-productive non-MRP waters; and (ii) warmer temperatures and higher zooplankton (prey) production in the MRP (versus non-MRP waters) would underlie this expected recruitment difference through “bottom-up” effects on larval growth. Peak larval yellow perch density was 10-fold and 5-fold less in the MRP than in non-MRP waters during 2006 and 2007, respectively. However, otolith microchemical analyses demonstrated that disproportionately more juvenile recruits emanated from the MRP than from non-MRP waters during both years. Although temperature and zooplankton production were higher in the MRP than in non-MRP waters during both years, observed recruitment differences were not definitively linked to bottom-up effects. Top-down effects also appeared important, as high turbidity in the MRP may offer a survival advantage by reducing predation mortality on larvae. Our research highlights the need to better understand biophysical coupling in freshwater systems and demonstrates how stochastic tributary inputs can influence fish recruitment.

This is the first study to report spectroscopic and elemental analysis of aragonite and vaterite growing simultaneously and separately in both the core and the edges of the same otolith. Our investigations focused on understanding differential trace metal uptake, including the influence of the metal itself (i.e., ionic radii), the crystalline structure, and the development state of the fish. Chemistry and crystal structure of sagittal otoliths from lake trout (Salvelinus namaycush) were studied using laser ablation combined with inductively coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectroscopy, respectively. Analyses of the composition of vaterite and aragonite growing in the same growth ring show that smaller cations like Mg (0.86 Å) (1 Å = 0.1 nm) and Mn (0.81 Å) were more abundant in the vaterite hexagonal crystal structure, whereas larger cations such as Sr (1.32 Å) and Ba (1.49 Å) were preferentially incorporated in aragonite (orthorhombic). Similarly, the coprecipitation of aragonite and vaterite in cores and edges allowed us to demonstrate that the uptake rates (as determined by element-specific partition coefficients) for Sr and Ba were greater in aragonite than vaterite, whereas those of Mg and Mn were higher in vaterite than in aragonite.