The phrase "a decrease in speciation" is correct and usable in written English.
It can be used in discussions related to biology, ecology, or conservation, particularly when addressing changes in the rate at which new species are formed.
Example: "The study highlighted a decrease in speciation due to habitat loss and climate change."
Alternatives: "a reduction in speciation" or "a decline in speciation".
Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in speciation.
That is, a relatively high, early rate of diversification followed by a decrease in speciation rate.
Thus, its use has been largely restricted to inferring a decrease in speciation rate over the history of the tree, which might indicate an early burst of diversification or adaptive radiation early in the history of the tree.
A popular method for inferring a decrease in speciation rate, which might suggest an early burst of diversification followed by a decrease in diversification rate is the γ statistic.
CR models incorporated either constant birth-death process (CR0), a decrease in speciation rate following a density-dependent process without extinction (CR1) or a decrease in speciation rate following a diversity-dependent process, including the estimation of extinction rate (CR2).
The comparison of different models of diversification using Bayes factor tests led to the selection of a two-rate pure-birth process and estimated a fourfold decrease in speciation rates (dropping from an initial 0.441 to 0.108), and indicating a substantial slowdown during the Miocene.
This rate is far lower than the previous rates, suggesting a decrease in the amount of speciation or an increase in the amount of extinction or both.
The observed pattern of a decrease in power associated with speciation, extinction, and character change when rates become increasingly asymmetrical is troubling.
First, a decrease in the rate of speciation may be due to diversity dependence, e.g. a niche-filling process, where new species reduce the probability of future speciation events [ 48].
Therefore, the association of duplication with speciation could be due to a rise in the duplication fixation rate upon speciation, caused by a decrease in the effective population size.
For instance, if the rapid early emergence of new species causes a decrease in niche space, then the opportunities for adaptive speciation decline, and slowdowns in ecological trait evolution would be expected given the reduced opportunities for adaptive niche expansions.
