The harvester ant M. wasmanni collects seeds for food and builds a nest composed mainly of seed husks. C. bicolor is a heat-tolerant desert foraging ant which eats dead insects and other arthropods. Interest focuses on whether there is evidence in the data for intra-species competition between Messor nests (i.e. competition for resources) and for preferential placement of Cataglyphis nests in the vicinity of Messor nests.
The full dataset is displayed in Figure 1 of Harkness \& Isham (1983).
See Usage below to produce a comparable plot.
It comprises 97 nests (68 Messor and 29 Cataglyphis)
inside an irregular convex polygonal boundary, together with
annotations showing a foot track through the region,
the boundary between field and scrub areas inside the
region, and indicating the two rectangular subregions
A and B used in their analysis.
Rectangular subsets of the data were analysed by
Harkness \& Isham (1983), Isham (1984), Takacs \& Fiksel
(1986), S\"arkk\"a (1993, section 5.3),
H\"ogmander and S\"arkk\"a (1999) and Baddeley \& Turner (2000).
The full dataset (inside its irregular boundary) was first analysed
by Baddeley \& Turner (2005b).
The dataset ants
is the full point pattern
enclosed by the irregular polygonal boundary.
The $x$ and $y$ coordinates are eastings (E-W) and northings (N-S)
scaled so that 1 unit equals 0.5 feet.
This is a multitype point pattern object, each point carrying a mark
indicating the ant species (with levels Cataglyphis
and Messor
).
The dataset ants.extra
is a list of auxiliary
information:
A
and B
trackNE
and trackSW
fieldscrub
side
function(x,y)
that determines whether the location
(x,y)
is in the scrub or the field. The function can be applied
to numeric vectors x
and y
, and returns a factor
with levels "scrub"
and "field"
.
This function is useful as a spatial covariate.
plotit
data(ants)
ants
is an object of class "ppp"
representing the full point pattern of ants' nests.
See ppp.object
for details of the format.
The coordinates are scaled so that 1 unit equals 0.5 feet.
The points are marked by species (with levels Cataglyphis
and Messor
). ants.extra
is a list with entries
"ppp"
"ppp"
list(x=numeric(2),y=numeric(2))
giving the two endpoints of line markingslist(x=numeric(2),y=numeric(2))
giving the two endpoints of line markingslist(x=numeric(2),y=numeric(2))
giving the two endpoints of line markingsx,y
www.jstatsoft.org
, ISSN: 1548-7660.Baddeley, A. and Turner, R. (2005b) Modelling spatial point patterns in R. In: A. Baddeley, P. Gregori, J. Mateu, R. Stoica, and D. Stoyan, editors, Case Studies in Spatial Point Pattern Modelling, Lecture Notes in Statistics number 185. Pages 23--74. Springer-Verlag, New York, 2006. ISBN: 0-387-28311-0.
Harkness, R.D. and Isham, V. (1983) A bivariate spatial point pattern of ants' nests. Applied Statistics 32, 293--303.
Hogmander, H. and Sarkka, A. (1999) Multitype spatial point patterns with hierarchical interactions. Biometrics 55, 1051--1058.
Isham, V.S. (1984) Multitype Markov point processes: some approximations. Proceedings of the Royal Society of London, Series A, 391, 39--53.
Takacs, R. and Fiksel, T. (1986) Interaction pair-potentials for a system of ants' nests. Biometrical Journal 28, 1007--1013.
Sarkka, A. (1993) Pseudo-likelihood approach for pair potential estimation of Gibbs processes. Number 22 in Jyvaskyla Studies in Computer Science, Economics and Statistics. University of Jyvaskyla, Finland.
# Equivalent to Figure 1 of Harkness and Isham (1983)
data(ants)
ants.extra$plotit()
# Data in subrectangle A, rotated
# Approximate data used by Sarkka (1993)
angle <- atan(diff(ants.extra$fieldscrub$y)/diff(ants.extra$fieldscrub$x))
plot(rotate(ants.extra$A, -angle))
# Approximate window used by Takacs and Fiksel (1986)
tfwindow <- boundingbox(Window(ants))
antsTF <- ppp(ants$x, ants$y, window=tfwindow)
plot(antsTF)
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