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Although parasites reduce host health, parasite infections also occur as a consequence of compromised host health. Both causalities could induce positive feedback, in which infected hosts with poor body conditions may suffer further infection, but it has rarely been demonstrated in the wild, possibly due to methodological difficulties. We used a mark-recapture survey combined with structural equation modelling (SEM) to examine whether both causalities and positive feedback occurred in stream salmonid and parasitic copepod systems. We found that parasitic copepods reduced host conditions and hosts with poor conditions were likely to be infected, suggesting that positive feedback can occur in the wild. Importantly, heavily infected hosts with poor body conditions showed lower apparent survival rates. Our findings provide robust evidence showing host condition–parasite infection dynamics, offering novel insights into how positive feedback could strongly undermine the wild host population via reduction of host survival.

This paper presents a single-chip SC line equalizer system, which can be applied to full duplex digital transmission. Adaptive SC filters, constructed with programmable capacitor arrays (PCAs), usually cause undesired responses, such as spike noise and transient response, which degrade data transmission quality. In order to avoid these phenomena, a duplex SC equalizer is introduced, which has the same circuits in parallel. PCAs in one duplex equalizer, whose output is not transfered, are varied. After the undesired phenomena vanish, the output is alternated. The equalizer system can be applied to several different bit rates,merely by changing the external control signals. An algorithm for a bridged tap echo canceller is modified for a more general case. A DC offset canceller and an auto zero circuit are employed for variable and fixed blocks, respectively. A line equalizer system was designed for four different bit rates, ranging from 3.2 to 64 kbps, and an LSI was fabricated using a 3Dm CMOS process. Chip area is 45.5 mm2, and power dissipation is 190 mW with a single +5V power supply.

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