Density dependence tests, are they?

A large number of time series of abundances of insects and birds from a variety of data sets were submitted to a new density dependence test. The results varied enormously between data sets, but the relation between the frequency of statistically significant density dependence (SSDD) and the length of the series was similar to that of the power curve of the test, making the results consistent with the hypothesis of the density-dependent model being universally applicable throughout the data used. Pest and non-pest species did not differ in the incidence of SSDD.

Trends in abundance of tropical forest insects.

The stability of a large variety of insect populations was studied using 14 years of light-trap data collected in a relatively undisturbed tropical forest in Panama. Special emphasis was placed on trends in abundance over time. A large between-species variation was found in stability, ranging from nearly constant to violently fluctuating.

Does lack of diapause result in less insect seasonality?

Unlike their temperate zone and tropical African relatives, flesh flies from the Neotropics lack the capacity for diapause. Yet, our trapping data reveal marked seasonality in flies from Panama, demonstrating that diapause is not essential for generating their seasonal patterns of abundance.

The equilibrium concept and density dependence tests What does it all mean?

Tests of density dependent regulation of population size depend on the concept of equilibrium population size. Such an equilibrium is a purely theoretical construct whose existence in the field is debatable and whose value cannot be measured. An equilibrium is supposed to fluctuate in time, but the extent of the fluctuations relative to those of the population size is unknowable.

Seasonal cues in tropical organisms. Rainfall? Not necessarily!

Activity seasons of tropical organisms often start, on the average, at or about the beginning of the rainy or dry seasons. The hypothesis that the onset or cessation of the wet season provides the seasonal cues necessary of the initiation of the activity season of some tropical organisms is tested with data on Panamanian cicadas. Seasonal adult activity patterns are described for cicada species in Panama, mostly from Barro Colorado Island (BCI), some from Las Cumbres.

Diversity, diversity indices and tropical cockroaches.

The diversity of samples of cockroaches (Blattaria) taken with light-traps in six localities in Panama is described. As a diversity index α of the log series is found to be more satisfactory than either N or N of Hills's series or Hurlbert's S , even if the distribution of the relative abundances is significantly different from a log series. However, even the α-index is of only limited usefulness.

Similarity indices, sample size and diversity.

The effect of sample size and species diversity on a variety of similarity indices is explored. Real values of a similarity index must be evaluated relative to the expected maximum value of that index, which is the value obtained for samples randomly drawn from the same universe, with the diversity and sample sizes of the real samples. It is shown that these expected maxima differ from the theoretical maxima, the values obtained for two identical samples, and that the relationship between expected and theoretical maxima depends on sample size and on species diversity in all cases, without exception.