Lake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we use 32 million temperature measurements from 139 lakes to quantify thermal habitat change (percentage of non-overlap) and assess how this change is exacerbated by potential habitat constraints. Long-term temperature change resulted in an average 6.2% non-overlap between thermal habitats in baseline (1978–1995) and recent (1996–2013) time periods, with non-overlap increasing to 19.4% on average when habitats were restricted by season and depth. Tropical lakes exhibited substantially higher thermal non-overlap compared with lakes at other latitudes. Lakes with high thermal habitat change coincided with those having numerous endemic species, suggesting that conservation actions should consider thermal habitat change to preserve lake biodiversity.

Post-embryonic development time, somatic growth, egg production rate, survival and sex ratio for the marine calanoid copepod Pseudocalanus newmani from the Pacific coast off southwestern Hokkaido were determined at five temperatures (3, 6, 10, 15 and 20°C) when a mixed algal diet was provided at satiating food condition (0.36 μg C ml⁻¹) in the laboratory. At temperatures between 3 and 15°C, the development time from hatching to adult female increased exponentially with decreasing temperature, being 23.3, 33.1, 46.7 and 74.6 days at 15, 10, 6 and 3°C, respectively. Males developed into adults 2–5 days earlier than did the females. At the highest temperature of 20°C, both embryonic and post-embryonic development and egg production of P. newmani were suppressed. This inhibitory effect of high temperature is consistent with the vertical distribution range and seasonal abundance cycle of this copepod in the field; it tends to avoid the warm surface layer (>15°C) and scarcely appears in the water column during summer and autumn. Body size of P. newmani was not affected by temperature until C1, but increased with decreasing temperature after C2. The weight-specific growth rate (SGR) increased linearly with temperature (T) until 15°C, which is expressed as SGR = 0.0095T + 0.0462 (r = 0.996). This growth pattern may also indicate high-temperature stress to this copepod, the general pattern of copepod growth being exponential. The weight-specific egg production rate (SER) also increased with temperature (SER = 0.02T + 0.014, r = 0.99), below 15°C. The proportion of male offspring of P. newmani that grew to adulthood was nearly 50% at 3 and 6°C, but decreased with increasing temperature at 10–15°C. This unequal sex ratio may be due to sex change during juvenile development under temperature control. These results suggest that temperature plays an important role in life history traits of P. newmani through not only temperature-dependent growth and reproduction, but also through high-temperature inhibition and temperature-controlled sex ratio under sufficient food supply.

Untangling causal links and feedbacks among biodiversity, ecosystem functioning, and environmental factors is challenging due to their complex and context-dependent interactions (e.g., a nutrient-dependent relationship between diversity and biomass). Consequently, studies that only consider separable, unidirectional effects can produce divergent conclusions and equivocal ecological implications. To address this complexity, we use empirical dynamic modeling to assemble causal networks for 19 natural aquatic ecosystems (N24^◦~N58^◦) and quantified strengths of feedbacks among phytoplankton diversity, phytoplankton biomass, and environmental factors. Through a cross-system comparison, we identify macroecological patterns; in more diverse, oligotrophic ecosystems, biodiversity effects are more important than environmental effects (nutrients and temperature) as drivers of biomass. Furthermore, feedback strengths vary with productivity. In warm, productive systems, strong nitrate-mediated feedbacks usually prevail, whereas there are strong, phosphate-mediated feedbacks in cold, less productive systems. Our findings, based on recovered feedbacks, highlight the importance of a network view in future ecosystem management.