Factors regulating kit fox populations

1997 ◽  
Vol 75 (12) ◽  
pp. 1982-1988 ◽  
Author(s):  
P. J. White ◽  
Robert A. Garrott
Keyword(s):  
Population Dynamics ◽  
Interference Competition ◽  
Survival Rates ◽  
Prey Abundance ◽  
Short Term ◽  
Density Dependent ◽  
Kit Fox ◽  
Vulpes Macrotis ◽  
Predominant Factor ◽  
Major Factors

Recent declines in several populations of kit foxes (Vulpes macrotis) have been attributed to decreased prey abundance and increased coyote-related mortalities. However, it is not known if short-term fluctuations in prey abundance or interference competition by coyotes can regulate the population dynamics of kit foxes. We coalesced data from all pertinent studies of kit and swift foxes and examined their numerical responses to changes in prey abundance. We also explored the influence of coyote-related mortalities on fox population dynamics. Fox density was positively correlated with leporid abundance, and fox reproduction rates were density-dependent at low prey densities. The proportion of the fox population killed by coyotes increased linearly over low to moderate fox densities, and survival rates of adult foxes decreased as the proportion of mortalities caused by coyotes increased. Hence, prey abundance and interference competition by coyotes may regulate fox populations. We suspect that prey abundance, and behavioral spacing mechanisms, are the major factors regulating fox densities. Coyote-related mortalities may be a less predominant factor, but could still act in concert with prey abundance to reduce the amplitude of fox population dynamics and keep foxes at lower densities than they might otherwise attain.

Population dynamics of kit foxes

1999 ◽  
Vol 77 (3) ◽  
pp. 486-493 ◽  
Author(s):  
P J White ◽  
Robert A Garrott
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Field Studies ◽  
High Amplitude ◽  
Short Term ◽  
Juvenile Mortality ◽  
Kit Fox ◽  
Fundamental Causes ◽  
Amplitude Fluctuations ◽  
Reproductive Rates

We evaluated data from field studies of kit foxes to identify factors that strongly influence or regulate their population dynamics. Two density-dependent regulating mechanisms were detected. First, the rate of juvenile recruitment was inversely related to the density of adult foxes because a higher proportion of juveniles were killed by coyotes at higher fox densities. The mortality rates of adult foxes were independent of population density. Second, populations of kit foxes are bounded by their territorial spacing behavior, which limits recruitment at high densities. These regulatory factors may operate in concert to curtail population growth at high densities, whereas decreased juvenile mortality by coyotes can operate independently to increase population growth at low densities. Despite the presence of these strong regulating factors, density-independent variations in reproductive rates often result in population crashes or irruptions that are the fundamental causes of instability in populations of kit foxes. Desert systems are characterized by unpredictable fluctuations in precipitation, which contribute to high-frequency, high-amplitude fluctuations in the abundance of mammalian prey (leporids, rodents) for kit foxes. These fluctuations subsequently contribute to density-independent variations in fox reproductive rates, which are strongly influenced by food supply. Projection models of a kit fox population showed that unpredictable, short-term fluctuations in precipitation and, in turn, prey abundance could generate longer term, aperiodic fluctuations in the density of foxes. Consequently, high amplitude fluctuations in the abundance of kit foxes may be intrinsic to the desert systems that they inhabit and need not reflect special or persistent causes such as predation or disease.

Persistence of giants: population dynamics of the limpet Scutellastra laticostata on rocky shores in Western Australia

2020 ◽  
Vol 646 ◽  
pp. 79-92
Author(s):  
RE Scheibling ◽  
R Black
Keyword(s):  
Population Dynamics ◽  
Western Australia ◽  
Size Structure ◽  
Survival Rates ◽  
Maximum Size ◽  
High Rate ◽  
Adult Survival ◽  
Rocky Shores ◽  
Adult Size ◽  
Decadal Time Scale

Population dynamics and life history traits of the ‘giant’ limpet Scutellastra laticostata on intertidal limestone platforms at Rottnest Island, Western Australia, were recorded by interannual (January/February) monitoring of limpet density and size structure, and relocation of marked individuals, at 3 locations over periods of 13-16 yr between 1993 and 2020. Limpet densities ranged from 4 to 9 ind. m-2 on wave-swept seaward margins of platforms at 2 locations and on a rocky notch at the landward margin of the platform at a third. Juvenile recruits (25-55 mm shell length) were present each year, usually at low densities (<1 m-2), but localized pulses of recruitment occurred in some years. Annual survival rates of marked limpets varied among sites and cohorts, ranging from 0.42 yr-1 at the notch to 0.79 and 0.87 yr-1 on the platforms. A mass mortality of limpets on the platforms occurred in 2003, likely mediated by thermal stress during daytime low tides, coincident with high air temperatures and calm seas. Juveniles grew rapidly to adult size within 2 yr. Asymptotic size (L∞, von Bertalanffy growth model) ranged from 89 to 97 mm, and maximum size from 100 to 113 mm, on platforms. Growth rate and maximum size were lower on the notch. Our empirical observations and simulation models suggest that these populations are relatively stable on a decadal time scale. The frequency and magnitude of recruitment pulses and high rate of adult survival provide considerable inertia, enabling persistence of these populations in the face of sporadic climatic extremes.

scholarly journals Robotic and laparoscopic liver surgery for colorectal liver metastases: an experience from a German Academic Center

2020 ◽  
Vol 18 (1) ◽  
Author(s):  
Mirhasan Rahimli ◽  
Aristotelis Perrakis ◽  
Vera Schellerer ◽  
Andrew Gumbs ◽  
Eric Lorenz ◽  
...  
Keyword(s):  
Abdominal Surgery ◽  
Minimally Invasive ◽  
Liver Surgery ◽  
Colorectal Liver Metastases ◽  
Survival Rates ◽  
Long Term Outcomes ◽  
Short Term ◽  
Minimally Invasive Liver Surgery ◽  
Previous Abdominal Surgery

Abstract Background Minimally invasive liver surgery (MILS) in the treatment of colorectal liver metastases (CRLM) is increasing in incidence. The aim of this work was to present our experience by reporting short-term and long-term outcomes after MILS for CRLM with comparative analysis of laparoscopic (LLS) and robotic liver surgery (RLS). Methods Twenty-five patients with CRLM, who underwent MILS between May 2012 and March 2020, were selected from our retrospective registry of minimally invasive liver surgery (MD-MILS). Thirteen of these patients underwent LLS and 12 RLS. Short-term and long-term outcomes of both groups were analyzed. Results Operating time was significantly longer in the RLS vs. the LLS group (342.0 vs. 200.0 min; p = 0.004). There was no significant difference between the laparoscopic vs. the robotic group regarding length of postoperative stay (8.8 days), measured blood loss (430.4 ml), intraoperative blood transfusion, overall morbidity (20.0%), and liver surgery related morbidity (4%). The mean BMI was 27.3 (range from 19.2 to 44.8) kg/m2. The 30-day mortality was 0%. R0 resection was achieved in all patients (100.0%) in RLS vs. 10 patients (76.9%) in LLS. Major resections were carried out in 32.0% of the cases, and 84.0% of the patients showed intra-abdominal adhesions due to previous abdominal surgery. In 24.0% of cases, the tumor was bilobar, the maximum number of tumors removed was 9, and the largest tumor was 8.5 cm in diameter. The 1-, 3- and 5-year overall survival rates were 84, 56.9, and 48.7%, respectively. The 1- and 3-year overall recurrence-free survival rates were 49.6 and 36.2%, respectively, without significant differences between RLS vs. LLS. Conclusion Minimally invasive liver surgery for CRLM is safe and feasible. Minimally invasive resection of multiple lesions and large tumors is also possible. RLS may help to achieve higher rates of R0 resections. High BMI, previous abdominal surgery, and bilobar tumors are not a barrier for MILS. Laparoscopic and robotic liver resections for CRLM provide similar long-term results which are comparable to open techniques.

scholarly journals Individual-based modelling of resource competition to predict density-dependent population dynamics: a case study with white storks

Oikos ◽  
2014 ◽  
Vol 124 (3) ◽  
pp. 319-330 ◽  
Author(s):  
Damaris Zurell ◽  
Ute Eggers ◽  
Michael Kaatz ◽  
Shay Rotics ◽  
Nir Sapir ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Resource Competition ◽  
Density Dependent ◽  
White Storks

Evolution of Surgical Approaches in the Treatment of Petroclival Meningiomas: A Retrospective Review

2007 ◽  
Vol 61 (suppl_5) ◽  
pp. ONS202-ONS211 ◽  
Author(s):  
Nicholas C. Bambakidis ◽  
U. Kumar Kakarla ◽  
Louis J. Kim ◽  
Peter Nakaji ◽  
Randall W. Porter ◽  
...  
Keyword(s):  
Survival Rates ◽  
Progression Free Survival ◽  
Surgical Approaches ◽  
Single Institution ◽  
Short Term ◽  
Total Resection ◽  
Free Survival ◽  
Petroclival Meningioma ◽  
Petroclival Meningiomas

Abstract Objective: We examined the surgical approaches used at a single institution to treat petroclival meningioma and evaluated changes in method utilization over time. Methods: Craniotomies performed to treat petroclival meningioma between September of 1994 and July of 2005 were examined retrospectively. We reviewed 46 patients (mean follow-up, 3.6 yr). Techniques included combined petrosal or transcochlear approaches (15% of patients), retrosigmoid craniotomies with or without some degree of petrosectomy (59% of patients), orbitozygomatic craniotomies (7% of patients), and combined orbitozygomatic-retrosigmoid approaches (19% of patients). In 18 patients, the tumor extended supratentorially. Overall, the rate of gross total resection was 43%. Seven patients demonstrated progression over a mean of 5.9 years. No patients died. At 36 months, the progression-free survival rate for patients treated without petrosal approaches was 96%. Of 14 patients treated with stereotactic radiosurgery, none developed progression. Conclusion: Over the study period, a diminishing proportion of patients with petroclival meningioma were treated using petrosal approaches. Utilization of the orbitozygomatic and retrosigmoid approaches alone or in combination provided a viable alternative to petrosal approaches for treatment of petroclival meningioma. Regardless of approach, progression-free survival rates were excellent over short-term follow-up period.

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