Prevention of Population Cycles by Parasite Removal

Abstract

dynamics of dissolved nutrient patches. We have yet to identify the frequency of occurrence and magnitude spectra of such patches in specific microbial food webs. They undoubtedly represent interesting ecological niches for bacteria, and they will also contribute much to our understanding of the flow of nutrients and energy in aquatic ecosystems if they prove to be major pathways.References and notes 1. J. C. Goldman, Bull. Mar. Sci. 35, 462 (1984). 2. E. M. Purcell, Am. J. Phys. 45, 3 (1977). 3. G. A. Jackson, Limnol. Oceanogr. 32, 1253(1987. 4. W. Bell and R. Mitchell, Biol. Bull. 143, 265 (1972 ѨC Ѩt where C is concentration, K D is a dissociation constant (100 M), and ␣ is a sensitivity constant (1000 s). Simulations were performed by allowing cells to move against a concentration field (3). Cells were moved a distance determined by their swimming velocity and heading angle from a physical location whose attractant concentration was C 1 to another location of concentration C 2 , within each simulated time step dt. The change in mean run duration could thus be calculated asNegative changes were ignored. Run durations are Poisson distributed (12). The probability of tumbling after each time step is dt/( ϩ ⌬). The desired Poisson process was implemented with a random generator to decide whether or not to tumble after each time step. Tumbles were simulated as reversals, and a Brownian rotation of 1 rad s Ϫ1 was introduced.Swimming velocities and mean run durations were acquired from tracks of live cells. 23. The steady-state concentration field C(r) was calculated as C͑r͒ ϭ E4D ͱr where oxygen exudation rate E ϭ 0.25 fmol s Ϫ1 was estimated from light-saturated photosynthesis of a cell 4 m in diameter. The diffusion coefficient D ϭ 10 Ϫ5 cm 2 s Ϫ1 . The inverse square-root dependency on the distance r from the source was introduced instead of inverse proportionality (3) to more closely approximate its shape in the flat chamber. 24. The concentration field C(r,t) of a spreading patch was calculated aswhere M is the amount of matter released (1 pmol The regular cyclic fluctuations in vertebrate numbers have intrigued scientists for more than 70 years, and yet the cause of such cycles has not been clearly demonstrated. Red grouse populations in Britain exhibit cyclic fluctuations in abundance, with periodic crashes. The hypothesis that these fluctuations are caused by the impact of a nematode parasite on host fecundity was tested by experimentally reducing parasite burdens in grouse. Treatment of the grouse population prevented population crashes, demonstrating that parasites were the cause of the cyclic fluctuations.

Revealing the role of predator interference in a predator–prey system with disease in prey population

“…Evidence from different other fields also support this hypothesis (Pulkkinen and Dieter, 2006). Various programs for the management of disease in natural populations also suggest the control of the diseased population through predation (Hudson et al, 1998;Choisy and Rohani, 2006;Greenman and Hoyle, 2010;Hawlena et al, 2010). On the other hand, there are also studies showing an increase in infection in prey populations due to the presence of predators (Holt and Roy, 2007;Bate and Hilker, 2013a).…”

“…Various programs for the management of disease in natural populations suggest the control of infection through predation (Hudson et al, 1998;Choisy and Rohani, 2006;Hawlena et al, 2010;Greenman and Hoyle, 2010). However, several theoretical and empirical evidence shows both increase and decrease of the infection prevalence of the disease due to the predation on infected population (Packer et al, 2003;Holt and Roy, 2007;Cá ceres et al, 2009).…”

To delay once or twice: the effect of hypobiosis and free-living stages on the stability of host–parasite interactions

“…Decreases in host fecundity mediated by the parasite are thought to be the main cause of these cycles. Accordingly, the potential effect of hypobiosis, related in the first paper, was not even evoked in the later one (Hudson et al 1998). Our own results confirm that hypobiosis should not have an important impact on the T. tenuis-red grouse interaction as we observed that for a level of aggregation as strong as that of T. tenuis (kZ1, Dobson & Hudson 1992) hypobiosis is expected to have no effect on the host population dynamics, irrespective of the proportion of arrested larvae (s) or the duration of arrestment (1/q).…”

“…Leaving apart the effect of the duration of hypobiosis, only a few specific host-parasite systems have the required properties to test our theoretical predictions of the effect of hypobiosis on the stability of hostparasite interactions. Dobson & Hudson (1992) and Hudson et al (1998) showed that the influence of the nematode parasite T. tenuis was necessary and sufficient to produce the observed cycles in the red grouse populations. Decreases in host fecundity mediated by the parasite are thought to be the main cause of these cycles.…”

Development and application of a delayed-release anthelmintic intra-ruminal bolus system for experimental manipulation of nematode worm burdens

“…However, the ability to reduce worm burdens experimentally is limited to the time when anthelmintics can be administered and the duration of the effective treatment period. Usually, a single oral dosing or injection is used to deliver the anthelmintic in the wild (Murray et al 1997;Hudson et al 1998;Irvine, 2000;Newey et al 2005;Pedersen and Greives, 2008) and the period of efficacy is generally a maximum of 3-5 weeks. However, slow-release intra-ruminal devices have been developed for livestock which deliver a therapeutic dose over a period of up to 100 days (Cardinal, 1997;Vandamme and Ellis, 2004) reducing both labour and material costs in the control of nematode parasites.…”