How much habitat does a river need? A spatially-explicit population dynamics model to assess ratios of ontogenetical habitat needs.

Restoration of spawning and juvenile habitats is often used to restore fish abundances in rivers, although often with unclear results. To study the effects of habitat limitations on the common barbel (Barbus barbus), a riverine litophilic cyprinid fish, an age-structured population model was developed. Using a Bayesian modeling approach, spawning and fry (0+ juvenile) habitat availability was integrated in the model in a spatially explicit way. Using Beverton-Holt and Ricker recruitment models, density dependence was incorporated in the spawning process and the recruitment of 0+ juveniles. Model parameters and their uncertainty ranges were obtained from reviewing the existing literature. The uncertainty of the processes was intrinsically accounted for by the inherently probabilistic nature of the Bayesian model. By testing various scenarios of habitat availabilities for the barbel, we hypothesize that improvement of the fish stock will be reached only at a well specified ratio of spawning to fry habitat. Model simulations revealed substantial abundance improvements at rather equal amounts of about 10% cover of both habitats, while even substantial improvements of either spawning or fry habitats only will result in little or no increase of abundance. Higher ratios of spawning to fry habitat were found to lower population recovery times. This work provides a tool that serves the assessment and comparison of river restoration scenarios as well as benchmarking rehabilitation targets in the planning phase. When targeting restoration of fish stocks, focusing only on one key life stage or process (such as spawning), without considering potential bottlenecks in other stages, can result in little to no improvement.

The influence of perceived causation on judgments of time: an integrative review and implications for decision-making.

RECENT RESEARCH HAS SHOWN THAT THE PERCEPTION OF CAUSALITY AFFECTS THE JUDGMENT OF ELAPSED TIME: an interval between an action and a subsequent event seems to be shorter when people believe that action has caused the event. This article reviews past work on the phenomenon and integrates the findings from the different settings in which it has been observed. The effect is found for actions people have personally taken, as well as for those they have simply read or heard about. It occurs for very short intervals (e.g., milliseconds) as well as longer periods (e.g., months or years). Beliefs and expectations about different types of causal forces and their trajectories over time can affect the degree of time compression in some settings. But the tendency toward compression of time is the default and dominant response: It persists when people think of generic causal relations and is enhanced when people opt for the quickest interpretation of causal relations. This robust influence of causality on time judgment appears to be linked to the basic tendency to rely on temporal proximity in processing causal relations and to people's early experience with the physical-mechanical world. Past work has focused primarily on the implications of time compression for the sense of agency, but this phenomenon has implications also for decisions that depend on time judgment. The compression of subjective time elapsed between actions and outcomes makes people more optimistically plan the timing of a focal action in the future, experience its effect earlier in the future, and be less likely to switch to an alternative course of action. The tendency toward compression can thus endow an action with a sort of privileged status or advantage.

Naïve theories of causal force and compression of elapsed time judgments.

Recent research has shown that when people perceive a causal relation between 2 events, they "compress" the intervening elapsed time. The present work shows that a naïve mechanical-physical conception of causality, in which causal forces are believed to dissipate over time, underlies the estimates of shorter elapsed time. Being primed with alternative, nondissipative causal mechanisms and having the cognitive capacity to consider such mechanisms moderates the compression effect. The studies rule out similarity, mnemonic association, and anchoring as alternative accounts for the effect. Taken together, the findings support the hypothesis that causal cognition plays a major role in judgments of elapsed time. The implications of the compression effect on the timing of future actions, persistence, and causal learning are discussed.

Perceived causality as a cue to temporal distance.

The three experiments reported show that judgments of elapsed time between events depend on perceived causal relations between the events. Participants judged pairs of causally related events to occur closer together in time than pairs of causally unrelated events that were separated by the same actual time interval. The causality-time relationship was first demonstrated for time judgments about historical events. Causally related events were judged to be significantly closer together in time than causally unrelated events. In two subsequent experiments, perceived causality was manipulated by providing expert information and by asking the participants themselves to imagine causal relationships between the to-be-judged events. Again, substantial and reliable effects of perceived causality were obtained. Our results suggest that people use strength of perceived causality as a cue to infer temporal distance.