In this article we consider simulation of appearance oscillations in abundance of biological species and concomitant abrupt changes in the population development process. The inductors for the appearance of many long-period fluctuations, such as herring cycles in the Pacific Ocean, have not yet been fully established. Changes in population cycles can take extreme nature and violate prevailing uniformity of biological diversity, even evoke significant impacts on ecosystems. Certain variation of abundance outbreaks can grow long enough in the form of series of peaks and lead to temporary habitat degradation. Spontaneous oscillations can occur in isolated laboratory populations without any external influence, while maintaining permanent experimental conditions. For the mathematical explanation of the internal mechanisms for the appearance of oscillatory regimes are used differential equations with delay. Widely known several such models Nicholson, Cushing, and Hutchinson equations – greater detail studied. Models show the occurrence of complicated forms of cycles after the Andronov–Hopf bifurcation. Features of relaxation oscillations in these models, like huge amplitude peaks at unreal depth lows, very few correspond to ecological reality. Burst to peak values of a population usually start after overcoming some threshold when suddenly action of mechanisms of regulation abruptly reduced. Modification of equation with delay remains an actual task for analysis of particular scenarios that are observed in reality for the population, such as the specific cases or insect outbreaks. We have proposed the modification of the Hutchinson model to describe the rare but critical for the condition of the forest scenario of population dynamics – the outbreak in the form of a series of peaks, but without intermediate minimums approaching to zero. Any outbreak of is a transient regime of existence of species within the ecosystem. Further, we have developed a basically different model, which involve one of the observed scenarios for completion of such process and reviewing the traditional interpretation of the parameter threshold capacity of environment. Relaxation oscillations occurring after the bifurcation in the new equation with increasing amplitude do not form a stable orbital cycle, but they are rapidly moving in infinitely increasing pseudo-periodic trajectory. The loss of properties of being dissipative trajectory is indicates fatal consequences for the existence of species in the local natural environment. Model with abnormal transition has practical significance in the description for the situations of invasion of alien species in isolated ecosystems and breeding of pests in agricultural areas already adapt to toxic chemicals. In the field of system ecology scenario of uncontrolled of resource exhaustion historically associated with the problem of Easter Island.