Spatial Distribution, Population Structure, and Predatory Impact of Gelatinous Predators on Zooplankton Community in Inshore Waters off Crimean Coast of the Black Sea

The study reports the data on the distribution and predatory impact of the gelatinous macroplankton on mesozooplankton in the inshore waters of Crimea in April 2016. In the study areas, gelatinous macroplankton comprised Scyphomedusae Aurelia aurita (Linnaeus, 1758) and three ctenophore species (Mnemiopsis leidyi A. Agassiz, 1865, Beroe ovata Bruguire, 1789, and Pleurobrachia pileus (O. F. Müller, 1776). The biomass of A. aurita dominated everywhere and varied from ~ 62 to 330 g·m‑2 in different areas. The largest A. aurita biomass was observed in the South Coast of Crimea and the smallest in Karkinitsky Bay, where the number of jellyfish was high, suggesting the predominance of small individuals in the population. The size structure of A. aurita population differed by region: the proportion of large animals increased from the West to the East. The abundance and biomass of M. leidyi were rather low: 0.33–1.45 ind·m‑2 and 1–51.7 g·m‑2, respectively (the exception was the position in the Kerch Strait, where M. leidyi abundance reached 2 ind. m‑2 and biomass 126.3 g·m‑2); that species occurred only at 33–45 % of the stations (the exception was Karkinitsky Bay – 17 %), with the maximum values in the South Coast of Crimea. Large, 55–70-mm, adult individuals predominated. P. pileus biomass was lower than the biomass of A. aurita and M. leidyi in all areas, but its abundance was much higher. The daily rations of A. aurita varied widely both in the entire area and from one region to another. The daily ration values correlated with the carbon content in A. aurita body. The predation pressure of A. aurita on zooplankton in the inshore waters of Crimea was very low and did not result in a crucial decrease in mesozooplankton abundance. The effect of M. leidyi, even with its low abundance and biomass, was much stronger

A Mathematical Model Supporting a Hyperpredation Effect in the Apparent Competition Between Invasive Eastern Cottontail and Native European Hare

In this work a mathematical model is built in order to validate on theoretical grounds field study results on a three-species system made of two prey, of which one is native and another one invasive, together with a native predator. Specifically, our results mathematically describe the negative effect on the native European hare after the introduction of the invasive Eastern cottontail, mediated by an increased predation rate by foxes. Two nonexclusive assumptions can be made: an increase in cottontail abundance would lead to a larger fox population, magnifying their predatory impact (“hyperpredation”) on hares; alternatively, cottontails attract foxes in patches where they live, which are also important resting sites for hares and consequently the increased presence of foxes results in a higher predation rates on hares. The model results support hyperpredation of increasing fox populations on native hares.

Population dynamics and predatory impact of the alien jellyfish Aurelia solida (Cnidaria, Scyphozoa) in the Bizerte Lagoon (southwestern Mediterranean Sea)

Understanding the life cycle strategies and predatory impact of alien jellyfish species is critical to mitigate the impact these organisms may have on local populations, biodiversity, and ultimately on the functioning of food webs. In the Mediterranean Sea, little is known about the dynamics of alien jellyfish, although this area is a biodiversity hotspot and one of the most threatened by an increasing number of alien jellyfish. Here, we investigated the population dynamics and predatory impact of a non-indigenous scyphomedusa, Aurelia solida Browne 1905, in the Bizerte Lagoon, Tunisia. The study was based on a bimonthly survey performed over two consecutive years, from November 2012 to August 2014. Field observations showed that the planktonic phase of A. solida occurs from winter to early summer. Prey composition was investigated by means of gut content and field zooplankton analyses. Calanoid copepods, mollusc larvae and larvaceans represented the main food items of A. solida. To determine the jellyfish feeding rate and their predatory impact on zooplankton populations, the digestion time for zooplankton prey was assessed at three different temperatures: 13, 18 and 23 °C in laboratory conditions, corresponding to the average range of temperatures encountered by A. solida in the Bizerte Lagoon. We found that A. solida consumed 0.5–22.5% and 0.02–37.3% of the daily zooplankton standing stock in 2013 and 2014, respectively. These results indicate a non-negligible but restricted seasonal grazing impact on some mesozooplankton groups, explained by the relatively short lifespan of the medusa stage (5–6 months).

Small mustelids in New Zealand: invasion ecology in a different world

This chapter reviews the ecology of the three species of small mustelids introduced into New Zealand: the ferret (Mustela furo), the stoat (M. erminea) and the weasel (M. nivalis), for biological control of rabbits. New Zealand offers a mosaic of environments totally different from those in which the three species evolved, including a diminishing array of endemic fauna especially vulnerable to mammalian predators. Mustelids in New Zealand display significant adaptive flexibility in diet, habitat selection, co-existence, dispersal, body size, population biology and predatory impact, with results contrasting with those observable in their northern-hemisphere ancestors. These evolutionary and ecological responses by mustelids to new opportunities are of considerable interest to evolutionary ecologists, especially those interested in competition and predator-prey relationships. Likewise, the need to protect New Zealand’s native fauna has stimulated extensive research on alternative options for mitigating the effects of invasive predators, applicable to pest management problems in other countries.