Delayed numerical response of goshawks to population fluctuations of forest grouse

SUMMARYThe impact of parasitism on population dynamics is determined in part by the numerical responses of parasites during population fluctuations of their hosts. Vole populations fluctuate in multi-annual cycles allowing such responses to be studied over successive phases of population growth, abundance and decline. We investigate how a helminth community (5 nematode and 7 cestode species) evolved over a full 6-year Water Vole (Arvicola terrestris) population cycle. Brillouin and individual parasite species richness (IPSR) indices were used to measure the numerical response of the parasite community. We report a correlation between levels of parasite intensity and vole population cycle phases. Both indices were consistently higher during pre-decline and decline phases for male and female voles alike. The numerical response of the parasite community suggests that populations may be regulated by parasitism and that studies of this mechanism should allow both for the cyclic or non-cyclic character of the host populations and for the response of the broadest possible set of the local parasite community.

Download Full-text

Population Fluctuations of Guadalupe Fur Seals (Arctocephalus philippii townsendi) Between the San Benito Islands and Guadalupe Island, Mexico, During 2009 and 2010

Aquatic Mammals ◽

10.1578/am.43.5.2017.492 ◽

2017 ◽

Vol 43 (5) ◽

pp. 492-500 ◽

Cited By ~ 2

Author(s):

Bertha García-Capitanachi ◽

Yolanda Schramm ◽

Gisela Heckel

Keyword(s):

Population Fluctuations ◽

Fur Seals ◽

Guadalupe Island

Download Full-text

Chesapeake Bay Stock Assessment: Who are they, and Where are they?

Water Science & Technology ◽

10.2166/wst.1992.0371 ◽

1992 ◽

Vol 26 (12) ◽

pp. 2705-2709 ◽

Cited By ~ 1

Author(s):

H. M. Austin

Keyword(s):

Chesapeake Bay ◽

Stock Assessment ◽

Human Consumption ◽

Population Fluctuations ◽

Important Species ◽

Fisheries Resources ◽

Environmentally Sensitive ◽

Climate Scale ◽

Resource And Environment

The Chesapeake Bay, while a significant habitat for fisheries resources, is in actuality an aquatic “bedroom community”, as many of the economically important species are seasonally transient. The pressure on these resources due to their demand for human consumption and recreation, proximity to extensive industrial activity along the shores, and climate scale environmental fluctuations has resulted in stock declines by most important species. Our inability to separate natural population fluctuations from those of anthropogenic origin complicates management efforts. The only way to make these separations, and subsequent informed management decisions is by supporting long-term stock assessment programs (monitoring) in the Bay which allow us to examine trends, cycles and stochastic processes between resource and environment. These programs need to monitor both recruitment and fishing mortality rates of the economically important species, and to identify and monitor the environmentally sensitive “canary” species.

Download Full-text

Impact of Males on the Numerical Response ofDiaeretiella rapae (M'Intosh) (Hym., Aphidiidae), a Parasitoid ofLipaphis erysimi Kalt. (Hem., Aphididae)

Mitteilungen aus dem Museum für Naturkunde in Berlin Zoologisches Museum und Institut für Spezielle Zoologie (Berlin) ◽

10.1002/mmnz.4830650111 ◽

1989 ◽

Vol 65 (1) ◽

pp. 161-169 ◽

Cited By ~ 1

Author(s):

Afroz Z. Abidi ◽

Arvind Kumar ◽

C. P. M. Tripathi

Keyword(s):

Numerical Response

Download Full-text

Declines and recovery in endangered Galapagos pinnipeds during the El Niño event

Scientific Reports ◽

10.1038/s41598-021-88350-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Diego Páez-Rosas ◽

Jorge Torres ◽

Eduardo Espinoza ◽

Adrian Marchetti ◽

Harvey Seim ◽

...

Keyword(s):

El Niño ◽

Environmental Variability ◽

El Nino ◽

Population Decline ◽

Annual Rate ◽

Population Fluctuations ◽

Galapagos Archipelago ◽

Population Decrease ◽

El Niño Event ◽

Zalophus Wollebaeki

AbstractCurrently, the Galapagos sea lion (GSL, Zalophus wollebaeki) and Galapagos fur seal (GFS, Arctocephalus galapagoensis) are among the most important endemic species for conservation in the Galapagos Archipelago. Both are classified as “Endangered” since their populations have undergone drastic declines over the last several decades. In this study we estimated the abundance of both otariids, and their population trends based using counts conducted between 2014 and 2018 in all their rookeries, and we analyzed the influence of environmental variability on pup production. The GSL population size in 2018 in the archipelago was estimated to be between 17,000 to 24,000 individuals and has increased at an average annual rate of 1% over the last five years after applying correction factors. The highest number of GSL counted in the archipelago was in 2014 followed by a population decline of 23.8% in 2015 that was associated with the El Niño event that occurred during that year. Following this event, the population increased mainly in the northern, central and southeastern rookeries. The GSL pup abundance showed a decreasing trend with the increase in intensity of the El Niño. The GFS population in 2018 was counted in 3,093 individuals and has increased at an annual rate of 3% from 2014 to 2018. A high number of GFS counted in 2014 was followed by a population decrease of 38% in 2015, mainly in the western rookeries. There was interannual population fluctuations and different growth trends among regions of the archipelago. GSL and GFS pup abundance has a strong decreasing tendency with the increase in the subthermocline temperature (ST) and the El Niño 1 + 2 index. Our results provide evidence that both species are highly vulnerable to periodic oceanographic-atmospheric events in the Galapagos Archipelago which impact prey abundance and the flow of energy in the unique Galapagos ecosystem.

Download Full-text

Contrasting Competitor and Predator Responses to a Short-Lived Southern Pine Beetle Outbreak: A Case Study

Forest Science ◽

10.1093/forsci/fxaa041 ◽

2020 ◽

Author(s):

Stephen R Clarke ◽

Jessica Hartshorn

Keyword(s):

Natural Enemy ◽

Bark Beetles ◽

Southern Pine Beetle ◽

National Forest ◽

Population Fluctuations ◽

Thanasimus Dubius ◽

Southern Pine ◽

Widespread Application ◽

Pine Beetle

Abstract The southern pine beetle (SPB) Dendroctonus frontalis Zimmermann, is the most important insect pest of pines in the southeastern United States, with outbreaks often resulting in thousands of hectares of pine mortality. Natural enemies and competitors have been cited as significant regulators of SPB populations and, therefore, outbreaks. A recent outbreak on the Homochitto National Forest (NF) in Mississippi provided an opportunity to undertake a case study comparing population fluctuations of SPB, its major predator Thanasimus dubius, and its competitors, Ips bark beetles. Trap catches of all three were tracked through the course of the outbreak on the Homochitto NF as well as in two other forests with low or no SPB activity. The number of predators collected initially increased on the Homochitto NF in response to the SPB outbreak, but their impact on reducing infestation numbers was unclear. Numbers of Ips trapped were similar across all three forests, indicating that other factors were regulating SPB populations. The outbreak only lasted a single year, and its brevity likely limited the availability of host resources for natural enemy and competitor populations. Additional studies are warranted to explore the mechanisms affecting the extent and duration of SPB outbreaks, such as active forest management. Study Implications: The widespread application of cut-and-leave treatments during a short duration southern pine beetle (SPB) outbreak on the Homochitto National Forest did not result in immediate increased collections of Ips bark beetles, competitors of SPB. Similar population trends of Ips bark beetles in areas with and without SPB infestations suggest that other factors, such as climate, regulate population numbers. Low numbers of the main SPB predator, Thanasimus dubius, immediately preceded an outbreak, and trap collections increased after outbreak onset, reaffirming the importance of this natural enemy in SPB population fluctuations.

Download Full-text