Tillering dynamics in spring and summer of marandu palisade grass pastures previously used under deferred grazing

ABSTRACT This work was conducted to evaluate the effect of deferred pasture condition of Brachiaria brizantha cv. Marandu in the late winter on tillering during the growing season. The treatments were three pasture conditions at late winter: short pasture, tall pasture and tall/mown pasture. In September and October, tiller appearance rate (TApR) and tiller mortality rate (TMoR) were greater in the tall/mown pasture. In November and December, tall pasture presented greater TApR. From November to January the TMoR was greater in the tall pasture. The tiller stability index of short and tall/mown pastures were greater in October. The short pasture presented a greater tiller number than the tall and tall/mown pastures during the entire experimental period. Deferred and short pasture of marandu palisade grass at late winter presents in general lower tiller mortality and higher population density of tillers from the early spring onwards, in comparison to tall pasture. The mowing of marandu palisade grass with high forage mass at the late winter, although it only temporarily compromises the population stability of tillers, also stimulates its fast tillering from spring on.

Intervention Time in Target-Oriented Chaos Control

The timing of interventions plays a central role in managing and exploiting biological populations. However, few studies in the literature have addressed its effect on population stability. The Seno equation is a discrete-time equation that describes the dynamics of single-species populations harvested according to the proportional feedback method at any moment between two consecutive censuses. Here we study a discrete-time equation that generalizes the Seno equation by considering the management and exploitation of populations through the target-oriented chaos control method. We investigate the combined effect of timing, targeting, and control on population stability, focusing on global stability. We prove that high enough control values create a positive equilibrium that attracts all positive solutions. We also prove that it is possible to determine parameter values to stabilize the controlled populations at any preset population size. Finally, we investigate the parameter combinations for which the management and exploitation are optimized in different scenarios.

Dots on Earth with huge genetic diversity: relict flatworm Crenobia alpinain the alpine lakes of Tatra Mountains

Mountain lakes, typical signs of an alpine landscape all around the world, were formed in the western part of the Carpathian Arch about 10,000-15,000 years ago, as remnants of the last continental glaciation. In the Tatra Mountains (Slovak-Polish border), more than 110 permanent lakes of glacial origin and many other small ponds exist. These (sub)alpine lakes, with their specific conditions, are very vulnerable and any change in their environment can largely impact their biodiversity, which is, despite long-term faunistic and ecological research, still not fully recognized. This shortcoming could be strongly improved by molecular approaches, which, even within population-genetic studies, often reveal unsuspected cryptic lineages or potential new species. Our long-term research is aimed at revealing the genetic diversity of aquatic macroinvertebrate species in the alpine environment of the Western Carpathians. One of the currently studied species is the glacial relict flatworm taxon Crenobia alpina (Dana, 1766) (Tricladida: Planariidae), representing an element of the permanent aquatic fauna. Totally, 88 COI haplotypes of C. alpina forming at least five well-separated genetic lineages were identified within 348 individuals collected from 45 lakes and ponds in theTatra Mts. Based on tests of selective neutrality and population stability, C. alpina populations in the Tatra lakes did not overcome recent population expansions or contractions. It seems that great genetic differences between localities and their population stability could be a consequence of the presence of natural topographic barriers (ridges, mountain peaks) dividing the mountains into small and relatively isolated valleys. Moreover, other important factors that could play a significant role are the limited dispersal ability of the species as well as its ability to reproduce asexually. Our findings were also compared with all publicly available sequences (Barcoding of Life Datasystems - BOLD and GenBank) in order to shift our data from a local to a holistic view on C. alpina. Our resultssupport the assumption of Brändle et al. 2017 that C. alpina represents a complex of cryptic lineages or species in Europe. As part of the AquaBOL.sk initiative, the data obtained contribute to the knowledge of genetic variability and barcoding of aquatic organisms in Slovakia.

Growth of Megathyrsus maximus cv. Mombaça as affected by grazing strategies and environmental seasonality. I. Tillering dynamics and population stability

In rotationally grazed pastures, the canopy light environment can be modulated through both grazing frequency and severity, and the magnitude of sward responses may differ according to forage species and its ability to use available resources. We hypothesised that the tall, tufted, fast-growing, tussock-forming species Mombaça guineagrass (Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs cv. Mombaça) can modulate its tillering dynamics and change its persistence pathway according to grazing strategy and the availability of growth factors. Treatments corresponded to all combinations of two levels of pre-grazing canopy light interception during regrowth (95% and maximum) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. A quite stable tiller population density presented regardless of the range of grazing frequency and severity used in the study. However, tiller appearance and death were strongly influenced (P < 0.001) by season of the year, with highest rates recorded during the two summers and lowest during autumn–winter. There was no conclusive evidence that the persistence pathway of Mombaça guineagrass changes within the grazing management strategies studied.