Population dynamics of the southern short-tailed opossum (Monodelphis dimidiata) in the Pampas of Argentina

2012 ◽  
Vol 60 (4) ◽  
pp. 238 ◽  
Author(s):  
Alejandro V. Baladrón ◽  
Ana I. Malizia ◽  
María S. Bó ◽  
María S. Liébana ◽  
Marc J. Bechard
Keyword(s):  
Population Dynamics ◽  
Average Density ◽  
Sudden Increase ◽  
Vegetative Cover ◽  
Reproductive Seasonality ◽  
Pampean Region ◽  
Live Trapping ◽  
Native Grassland ◽  
Polygynous Mating System ◽  
Stable Populations

The genus Monodelphis is one of the most species rich among Neotropical marsupials. Despite this, little is known about most of the species. One of the most enigmatic species is M. dimidiata, a small terrestrial opossum that inhabits the Pampean region of Argentina, which is suspected to be a semelparous breeder. From 2005 to 2008, we conducted seasonal live trapping in near-pristine marshy grasslands and agroecosystems of the Pampean region in order to evaluate the population trends of this species and the occurrence of semelparity. M. dimidiata was characterised by a low abundance in the study area. The average density was higher in grasslands than in agroecosystems, and it appeared to be influenced by vegetative cover. The onset of the breeding season occurred during spring when the opossums showed a sudden increase in body size. Given that mature individuals were not found beyond autumn, the findings suggest an annual cycle for this species. In addition, this abrupt maturation resulted in a pronounced sexual dimorphism that, together with the strong reproductive seasonality and a likely polygynous mating system, supported previous claims that the species is semelparous. Our results also emphasise the importance of native grassland habitat for the maintenance of stable populations of M. dimidiata.

A simple model for ferret population dynamics and control in semi-arid New Zealand habitats

2001 ◽  
Vol 28 (1) ◽  
pp. 87 ◽  
Author(s):  
N. D. Barlow ◽  
G. L. Norbury
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Current Density ◽  
Average Density ◽  
Intrinsic Rate Of Increase ◽  
Data Sets ◽  
Data Set ◽  
Rate Of Increase ◽  
Semi Arid ◽  
Over Time

Introduced ferrets (Mustela furo) in New Zealand are subject to population control to reduce their threat to native fauna and the incidence of bovine tuberculosis (Tb) in livestock. To help in evaluating control options and to contribute to a multi-species model for Tb dynamics, a simple Ricker model was developed for ferret population dynamics in a semi-arid environment. The model was based on two data sets and suggested an intrinsic rate of increase for ferrets of 1.0–1.3 year–1 and a carrying capacity of 0.5–2.9 km–2. There was evidence for direct density-dependence in both data sets and the effect appeared to act mainly on recruitment. Dependence of the rate of increase of predators on the density of wild rabbits (Oryctolagus cuniculus) was exhibited in one of the two data sets, together with a numerical response relating current density of predators asymptotically to current density of rabbits, their primary prey. Predators in this data set included both cats and ferrets, estimated from spotlight counts, but the other data set demonstrated a direct proportionality between predator (cat and ferret) spotlight counts and minimum ferrets known to be alive by trapping. The model suggested, firstly, that populations are hard to suppress by continuous culling, with at least a 50% removal per year necessary to effect a suppression of 50% in long-term average density. Secondly, if control is episodic rather than continuous, culling in autumn gives a greater degree of suppression over time (280%, accumulated over time) than culling in spring (180%). A differential equation version of the model provides a component for a general Anderson/May bovine Tb/wildlife (possum/deer/ferret) model.

The ecology of the deer mouse Peromyscus maniculatus in a coastal coniferous forest. I. Population dynamics

1974 ◽  
Vol 52 (1) ◽  
pp. 107-118 ◽  
Author(s):  
B. G. Petticrew ◽  
R. M. F. S. Sadleir
Keyword(s):  
Population Dynamics ◽  
Breeding Season ◽  
Deer Mouse ◽  
Coniferous Forest ◽  
Deer Mice ◽  
Population Parameters ◽  
Male Behavior ◽  
Mature Forest ◽  
Live Trapping ◽  
Breeding Seasons

A 3-year live-trapping study of deer mice was carried out on separate 1-hectarc (ha) grids located in a mature forest, a recently logged area, and a young plantation. Despite apparent gross differences in the habitats, populations on the recently logged area were similar in numbers, survival, and recruitment to those in the mature forest. There were greater differences in population parameters between years than between these two areas. Populations of deer mice in the young plantation were lower in numbers and eventually went to extinction in the summer of 1970. This appeared to be due rather to the presence of numerous Microtus oregoni in this area than to the habitat being less suitable for deer mice.On the basis of this and previous studies it is proposed that the numbers of deer mice in a population are regulated as follows. During breeding seasons the numbers of males and juveniles are regulated by agonistic male behavior while the numbers of females may be a function of the length of the breeding season. During non-breeding seasons the changes in numbers of all deer mice are regulated by the length of such seasons.

scholarly journals Effects of Vegetative Cover on the Population Dynamics of Meadow Voles

1996 ◽  
Vol 77 (3) ◽  
pp. 857 ◽  
Author(s):  
John D. Peles ◽  
Gary W. Barrett
Keyword(s):  
Population Dynamics ◽  
Vegetative Cover ◽  
Meadow Voles

Effect of resident vegetation on establishment of surface sown pasture species at Glen Innes, New South Wales

1978 ◽  
Vol 18 (92) ◽  
pp. 411
Author(s):  
PM Dowling
Keyword(s):  
Field Experiment ◽  
Festuca Arundinacea ◽  
New South ◽  
New South Wales ◽  
Trifolium Subterraneum ◽  
Quadratic Equation ◽  
Vegetative Cover ◽  
South Wales ◽  
Native Grassland ◽  
The Relationship

The influence of resident vegetative cover on the establishment of surface sown seed was determined in a field experiment at Glen Innes, New South Wales. Seed was sown on 25 occasions over a period of 2 years spanning the period November 1969 to January 1972. Species sown were Phalaris aquatica, Festuca arundinacea, Medicago sativa and Trifolium subterraneum. The relationship between mean per cent establishment and vegetative cover was significant and was described by the quadratic equation y = 0.8064 � 9.8342x - 0.8829x2. Presence of vegetative cover significantly increased mean establishment on 22 occasions. Presence of Sorghum leiocladum plants as a component of the resident vegetation had a larger influence on establishment of surface sown species than Bothriochloa ambigua and Poa sieberana. It was concluded that the best means of obtaining maximum establishment of surface sown pasture species in native grassland areas on the Northern Tablelands of New South Wales was by sowing into vegetative cover (approximately 5000 kg ha-1) and sowing during the period May-July.

scholarly journals Small-scale spatial structure influences large-scale invasion rates

2019 ◽  
Author(s):  
Michael J. Plank ◽  
Matthew J. Simpson ◽  
Rachelle N. Binny
Keyword(s):  
Population Dynamics ◽  
Spatial Structure ◽  
Large Scale ◽  
Spatial Scales ◽  
Mean Field ◽  
Average Density ◽  
Small Scale ◽  
Local Interactions ◽  
Mean Field Model ◽  
Species Invasions

AbstractLocal interactions among individual members of a population can generate intricate small-scale spatial structure, which can strongly influence population dynamics. The two-way interplay between local interactions and population dynamics is well understood in the relatively simple case where the population occupies a fixed domain with a uniform average density. However, the situation where the average population density is spatially varying is less well understood. This situation includes ecologically important scenarios such as species invasions, range shifts, and moving population fronts. Here, we investigate the dynamics of the spatial stochastic logistic model in a scenario where an initially confined population subsequently invades new, previously unoccupied territory. This simple model combines density-independent proliferation with dispersal, and density-dependent mortality via competition with other members of the population. We show that, depending on the spatial scales of dispersal and competition, either a clustered or a regular spatial structure develops over time within the invading population. In the short-range dispersal case, the invasion speed is significantly lower than standard predictions of the mean-field model. We conclude that mean-field models, even when they account for non-local processes such as dispersal and competition, can give misleading predictions for the speed of a moving invasion front.

Reproduction of Richardson's ground squirrel (Spermophilus richardsonii) in southern Saskatchewan

1972 ◽  
Vol 50 (12) ◽  
pp. 1577-1581 ◽  
Author(s):  
D. H. Sheppard
Keyword(s):  
Sex Ratio ◽  
Litter Size ◽  
Ground Squirrel ◽  
Ground Squirrels ◽  
Spermophilus Richardsonii ◽  
Live Trapping ◽  
Native Grassland ◽  
Adult Sex Ratio ◽  
The Mean ◽  
Sexually Mature

Adult Richardson's ground squirrels (n = 238) were collected near Regina, Saskatchewan in April and May of 1969 and 1970. The adult sex ratio (males: females) of collected animals was 1:3.3 compared with a juvenile sex ratio of 1:1 obtained by live trapping in 1967and 1968. The breeding season extended from 3 to 28 April but 77.8% of all conceptions occurred between 7 and 16 April. All yearlings seemed to be sexually mature and the mean litter size for all females baaed on living embryos was 6.93 ± 0.18. Mortality of embryos was 6.83%. Yearlings were smaller than adults but mean litter sizes of yearlings and adults did not differ. Ground squirrels collected from cropland had a significantly larger mean litter size, were somewhat heavier, and had significantly longer humeri than those from native grassland.

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