title: The effects of delay-to-reinforcement, response requirement and schedule duration on performance under fixed-ratio schedules

authors: Harris, Aimee Rebecca

subjects: fixed-ratio schedules

abstract: Experiment 1 examined the effects of delay-to-reinforcement on between-ratio pausing in multiple fixed-ratio 5 fixed-ratio 5 schedules. In one component the reinforcer was delivered immediately on completion of the ratio, and in the other there was a delay before reinforcement. The longest between-ratio pauses always preceded the ratio in which the delay was signalled, and these pauses increased as the delay increased. Experiment 2 examined the effects of varying delay-to-reinforcement on behaviour under fixed-ratio schedules that were increased each session, keeping the time available for responding constant. At each ratio requirement, with increased delay, total consumption and response rates decreased and between-ratio pause durations increased, although this effect was small. Functions were fitted to the relation between the natural logarithms of the consumption and fixed-ratio size using Hursh, Raslear, Shurtleff, Bauman and Simmonds’s (1988) nonlinear and Hursh and Silberberg’s (2008) exponential equations. Both fitted the data well, but in neither case did any of the parameters vary systematically with delay. The only consistent finding was that initial consumption was largest when there was no delay and smallest in the condition with the largest delay. This suggests a decreasing effect of delay-to-reinforcement with increases in the response requirement. Experiment 3 used conjunctive fixed-ratio fixed-interval schedules to separate the effects of schedule duration and ratio requirement in increasing fixed-ratio schedules. The schedule-initiation immediacies (the inverse of the pause following reinforcement) decreased in conditions in which the ratio was fixed and duration increased, and remained relatively constant in conditions in which the ratio was increased and duration fixed. It is suggested that the schedule-initiation immediacy is a useful measure as it eliminates some of the confounds of measures such as total consumption or consumption rate. These experiments show that with some procedures delay-to-reinforcement affects behaviour under fixed-ratio schedules in a way similar to reduced reinforcer magnitude and an increased force requirement. However, with other procedures, delay-to-reinforcement has different effects from reinforcer magnitude and quality. Also, overall, these three experiments show that increased time to reinforcement (whether as part of schedule requirements or at the end of the response requirement) has a larger effect on behaviour than the number of responses it takes to complete the ratio.

text: The effects of delay-to-reinforcement, response requirement and schedule duration on performance under fixed-ratio schedules Experiment 1 examined the effects of delay-to-reinforcement on between-ratio pausing in multiple fixed-ratio 5 fixed-ratio 5 schedules. In one component the reinforcer was delivered immediately on completion of the ratio, and in the other there was a delay before reinforcement. The longest between-ratio pauses always preceded the ratio in which the delay was signalled, and these pauses increased as the delay increased. Experiment 2 examined the effects of varying delay-to-reinforcement on behaviour under fixed-ratio schedules that were increased each session, keeping the time available for responding constant. At each ratio requirement, with increased delay, total consumption and response rates decreased and between-ratio pause durations increased, although this effect was small. Functions were fitted to the relation between the natural logarithms of the consumption and fixed-ratio size using Hursh, Raslear, Shurtleff, Bauman and Simmonds’s (1988) nonlinear and Hursh and Silberberg’s (2008) exponential equations. Both fitted the data well, but in neither case did any of the parameters vary systematically with delay. The only consistent finding was that initial consumption was largest when there was no delay and smallest in the condition with the largest delay. This suggests a decreasing effect of delay-to-reinforcement with increases in the response requirement. Experiment 3 used conjunctive fixed-ratio fixed-interval schedules to separate the effects of schedule duration and ratio requirement in increasing fixed-ratio schedules. The schedule-initiation immediacies (the inverse of the pause following reinforcement) decreased in conditions in which the ratio was fixed and duration increased, and remained relatively constant in conditions in which the ratio was increased and duration fixed. It is suggested that the schedule-initiation immediacy is a useful measure as it eliminates some of the confounds of measures such as total consumption or consumption rate. These experiments show that with some procedures delay-to-reinforcement affects behaviour under fixed-ratio schedules in a way similar to reduced reinforcer magnitude and an increased force requirement. However, with other procedures, delay-to-reinforcement has different effects from reinforcer magnitude and quality. Also, overall, these three experiments show that increased time to reinforcement (whether as part of schedule requirements or at the end of the response requirement) has a larger effect on behaviour than the number of responses it takes to complete the ratio.

year: 2011

title: Macrophyte architecture affects the abundance and diversity of littoral microfauna

authors: Lucena-Moya, Paloma

subjects: zooplankton

abstract: We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

text: Macrophyte architecture affects the abundance and diversity of littoral microfauna We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

year: 2011

title: Can large taonga bivalves speed up recovery in degraded estuaries?

authors: Prinz, Natalie

abstract: THE QUESTION:
Will there introduction of adult, long-lived bivalves with differing functional traits speed up recovery of degraded soft sediment habitats in estuaries?
RESULTS:
Average bivalve survival after one year was 18% in + tuangi plot sand 59% in + hanikura plots. Sediment oxygen consumption (SOC) after one month was enhanced by 116% in treatments containing tuangi compared to control treatments. After one year those were similar to ambient levels, still showed higher SOC than control plots.

text: Can large taonga bivalves speed up recovery in degraded estuaries? THE QUESTION:
Will there introduction of adult, long-lived bivalves with differing functional traits speed up recovery of degraded soft sediment habitats in estuaries?
RESULTS:
Average bivalve survival after one year was 18% in + tuangi plot sand 59% in + hanikura plots. Sediment oxygen consumption (SOC) after one month was enhanced by 116% in treatments containing tuangi compared to control treatments. After one year those were similar to ambient levels, still showed higher SOC than control plots.

year: 2023