Abstract
Anderson, M.J. 2008. Animal-sediment
relationships
revisited: characterising species’
distributions
along an environmental gradient using canonical analysis and quantile regression splines. Journal of Experimental
Marine Biology and Ecology.
in press.
Benthic
soft-sediment organisms generally show strong relationships with the
grain-size
characteristics of the sediments they inhabit. These relationships,
when characterised from field data, tend
to be asymmetrical,
non-linear and heteroscedastic, due to the
existence
of multiple other potentially important and interacting factors, some
of which
are inevitably unmeasured. For multivariate data, canonical analysis of
principal coordinates (CAP) can be used to isolate particular gradients
of
interest, despite the presence of other potentially important factors.
For univariate abundance data, models
focusing on upper quantiles of species'
distributions can ameliorate the
problem of heterogeneity induced by other variables. Here, a
multivariate model
of the relationship between benthic inter-tidal estuarine soft-sediment
assemblages (sampled over a period of 3 years from 70 sites across the Auckland region)
and the
percentage of mud in the sediments was generated using CAP. To characterise changes in assemblage structure, quantile regression splines
(of
the 0.95 quantile) were used to model each
of the twenty
most abundant individual taxa along the
gradient in
percentage mud. This approach provided an effective instrumental
quantitative
predictive model of species' turnover, while allowing for the
asymmetric,
non-linear animal-sediment relationships and heterogeneous scatter
observed in
species' abundances along the mud gradient.
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Abstract
Lear,
G., Anderson,
M.J., Smith, J.P., Boxen, K. and Lewis,
G.D. 2008. Spatial and temporal heterogeneity of
the bacterial communities in
stream epilithic biofilms.
FEMS Microbiology Ecology 65: 463-473.
The
spatial and temporal variability in bacterial communities within
freshwater
systems is poorly understood. The bacterial composition of stream epilithic biofilms
across a range
of different spatial and temporal scales both within and between
streams and
across the profile of individual stream rocks was characterized using a
community DNA-fingerprinting technique (Automated Ribosomal Intergenic
Spacer Analysis ARISA). The differences in bacterial community
structure
between two different streams were found to be greater than the spatial
variability within each stream site, and were larger than the weekly
temporal
variation measured over a 10-week study period. Greater variations in
bacterial
community profiles were detected on different faces of individual
stream rocks
than between whole rocks sampled within a 9-m stream section. Stream
temperature was found to be the most important determinant of bacterial
community variability using distance-based redundancy analysis (dbRDA) of ARISA data, which may have broad
implications for
riparian zone management and ecological change as a consequence of
global
warming. The combination of ARISA with multivariate statistical methods
and
ordination, such as multidimensional scaling (MDS), permutational
MANOVA and RDA, provided rapid and effective methods for quantifying
and
visualizing variation in bacterial community structure, and to identify
potential drivers of ecological change.
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Abstract
Cullen, L.E., Adams, M.A., Anderson,
M.J. and Grierson, P.F. 2008.
Analyses of d13C
and d18O
in tree rings of Callitris columellaris
provide evidence of a change in stomatal
control of
photosynthesis in response to regional changes in climate. Tree
Physiology 28: 1525-1533.
We
examined relationships between stable isotopes of carbon (δ13C)
and oxygen (δ18O) in tree rings of Callitris columellaris
F. Muell
in the semi-arid Pilbara region of north-western Australia. To test the
hypothesis
that stomatal control of photosynthesis
decreases
during drier periods, we developed δ13C and δ18O
chronologies spanning 1919–1999, and used a permutation regression
approach to relate a 21-year running correlation between δ13C
and δ18O to rainfall and temperature at Marble Bar and our
study site. The relationship between δ13C and δ18O
switched from being always negative before 1955 to being consistently
positive
after 1976, suggesting an increase in stomatal
control of photosynthesis in recent decades. Changes in the δ13C–δ18O
relationship reflected changes in rainfall, which has increased in the
region
by 30% since 1976. The correlation between δ13C and δ18O
was positively related to the 21-year running mean of normalized
rainfall
anomalies at both the study site (P =
0.045, Adj. r2 = 0.47) and
Marble Bar (P = 0.046, Adj. r2
= 0.48). In addition, the
δ13C–δ18O correlation was negatively
related (P = 0.047, Adj. r2
= 0.61) to temperatures at
Marble Bar. Our interpretation of the role of changes in climate
affecting the
relationship between tree-ring δ13C and δ18O is
supported by evidence from the isotope composition of foliage samples:
foliar
δ13C and δ18O were negatively correlated with
log stomatal conductance (δ13C,
r = –0.41; δ18O, r =
–0.42), whereas the
correlation between foliar δ13C and δ18O was
positive
(r = 0.63, P = 0.027) after the summer
wet period. Our data indicate that stomatal
control of photosynthesis in Callitris
adjusts to region-wide
changes in climate and that, in a warmer and drier world, trees might
adapt by
increasing non-stomatal control of
photosynthesis.
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Abstract
Watson, D.L., Harvey,
E.S.,
Kendrick, G.A., Nardi, K. and Anderson, M.J.
2007. Protection from
fishing alters the species composition of fish assemblages in a
temperate-tropical transition zone. Marine
Biology 152: 1197-1206.
Closure
of areas to fishing is expected to result in an increase in the
abundance of
targeted species; however, changes to populations of species not
targeted by
fishermen will depend upon their role in the ecosystem and their
relationship
with targeted species. The effects of protection on targeted and
non-targeted
reef fish species at the Houtman Abrolhos
Islands, Western Australia were studied using baited remote underwater
stereo–video cameras. Video images were collected from shallow (8–12
m) and deep (22–26 m) reef sites inside a Marine Protected Area (MPA)
at
each of three island groups and from three replicate fished locations
at each
of these groups that span a temperate-tropical transition area. The MPAs were established in 1994 and vary in size
from 13.72
km2 at the Pelsaert group in
the south to
22.29 km2 at the Easter group to 27.44 km2 at the
Wallabi group in the north. The relative
abundances of 137
fish species from 42 families were recorded. Large differences in fish
assemblage structure existed between MPA and fished locations, and also
between
shallow and deep regions. Targeted fish species Plectropomus leopardus,
Lethrinus miniatus, Lethrinus nebulosus, Pagrus auratus and Glaucosoma hebraicum were more
abundant inside MPAs than in areas open to
fishing. Their abundance inside MPAs was
between 1.13 and 8 times greater than their
abundance at fished locations. For non-targeted fish species many were
more
abundant in areas open to fishing, e.g. Coris auricularis, Thalassoma lutescens,
Thalassoma lunare, Dascyllus trimaculatus, however
others were
conversely more abundant inside MPAs, e.g.
Gymnothorax spp, Kyphosus sydneyanus, Scarus microhinos, Chromis westaustralis,
Chaetodon
spp. This study demonstrates that the removal of abundant targeted
species from
an ecosystem by fishing can indirectly impact non-fished species and
alter the trophic structure of fish
assemblages.
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Abstract
McGill,
B., Etienne, R., Gray, J., Alonso, D., Anderson,
M., Benecha, H., Dornelas,
M., Enquist, B., Green, J., He, F., Hurlbert, A., Magurran,
A., Marquet, P., Maurer, B., Ostling,
A., Soykan, C., Ugland,
K.,
White, E. 2007. Species abundance distributions: moving beyond single
prediction
theories to integration within an ecological framework. Ecology
Letters 10: 995-1015.
Species
abundance distributions (SADs) follow one
of ecology’s
oldest and most universal laws – every community shows a hollow curve
or
hyperbolic shape on a histogram with many rare species and just a few
common
species. Here, we review theoretical, empirical and statistical
developments in
the study of SADs. Several key points
emerge. (i) Literally dozens of models have
been proposed to explain
the hollow curve. Unfortunately, very few models are ever rejected,
primarily
because few theories make any predictions beyond the hollow-curve SAD
itself.
(ii) Interesting work has been performed both empirically and
theoretically,
which goes beyond the hollow-curve prediction to provide a rich variety
of
information about how SADs behave. These
include the
study of SADs along environmental
gradients and
theories that integrate SADs with other
biodiversity
patterns. Central to this body of work is an effort to move beyond
treating the
SAD in isolation and to integrate the SAD into its ecological context
to enable
making many predictions. (iii) Moving forward will entail understanding
how
sampling and scale affect SADs and
developing
statistical tools for describing and comparing SADs.
We are optimistic that SADs can provide
significant
insights into basic and applied ecological science.
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Abstract
Atalah, J., Otto, S., Anderson,
M.J., Costello, M.J., Lenz, M. and Wahl, M. 2007. Temporal variance of
disturbance did not affect diversity and structure of a marine fouling
community in north-eastern New Zealand. Marine
Biology 153: 199-211.
Natural
heterogeneity in ecological parameters, like population abundance, is
more
widely recognized and investigated than variability in the processes
that
control these parameters. Experimental ecologists have focused mainly
on the
mean intensity of predictor variables and have largely ignored the
potential to
manipulate variances in processes, which can be considered explicitly
in
experimental designs to explore variation in causal mechanisms. In the
present
study, the effect of the temporal variance of disturbance on the
diversity of
marine assemblages was tested in a field experiment replicated at two
sites on
the northeast coast of New Zealand. Fouling
communities grown on
artificial settlement substrata experienced disturbance regimes that
differed
in their inherent levels of temporal variability and timing of
disturbance
events, while disturbance intensity was identical across all levels.
Additionally, undisturbed assemblages were used as controls. After 150
days of
experimental duration, the assemblages were then compared with regard
to their
species richness, abundance and structure. The disturbance effectively
reduced
the average total cover of the assemblages, but no consistent effect of
variability in the disturbance regime on the assemblages was detected.
The
results of this study were corroborated by the outcomes from
simultaneous
replicate experiments carried out in each of eight different biogeographical regions around the world.
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Abstract
Wheldon, M.C., Anderson,
M.J. and
Johnson, B.W. 2007. Identifying treatment
effects in
multi-channel measurements in electroencephalographic studies:
multivariate
permutation tests and multiple comparisons. Australian
& New Zealand Journal of Statistics 49: 397-413.
A
versatile procedure is described comprising an application of
statistical
techniques to the analysis of the large, multi-dimensional data arrays
produced
by electroencephalographic (EEG) measurements of human brain function.
Previous
analytical methods have been unable to identify objectively the precise
times
at which statistically significant experimental effects occur, owing to
the
large number of variables (electrodes) and small number of subjects, or
have
been restricted to two-treatment experimental designs. Many time-points
are
sampled in each experimental trial, making adjustment for multiple
comparisons
mandatory. Given the typically large number of comparisons and the
clear
dependence structure among time-points, simple Bonferroni-type
adjustments are far too conservative. A three-step approach is
proposed: (i) summing univariate
statistics across
variables; (ii) using permutation tests for treatment effects at each
time-point; and (iii) adjusting for multiple comparisons using
permutation
distributions to control family-wise error across the whole set of
time-points.
Our approach provides an exact test of the individual hypotheses while
asymptotically controlling family-wise error in the strong sense, and
can
provide tests of interaction and main effects in factorial designs. An
application to two experimental data sets from EEG studies is
described, but
the approach has application to the analysis of spatio-temporal
multivariate data gathered in many other contexts.
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Abstract
Oppenheimer, S., Astheimer, L., Anderson, M.J. and Buttemer, B. 2007. Morphometric
measures as a moderate predictor of gender in
the White-browed Babbler Pomatostomus
superciliosus gilgandra.
Corella 31: 15-18.
White-browed Babblers have monomorphic
plumage but exhibit size and weight dimorphism. Males are heavier, have
longer
tarsi, wings, and culmens than females.
Two hundred
and eighty-three White-browed Babblers from the central western region
of NSW
were sexed using laparotomy, and discriminant
function analysis was used to determine the extent to which morphometric
data could be used to identify gender. Cross-validation using a
jackknife
procedure indicated that 81 percent of males and 84 percent of females
were
correctly identified using the resultant discriminant
function. Culmen length contributed most
to the
classification of gender, followed by wing length and tarsus length.
The discriminant function is presented as
a potentially useful,
non-invasive, and inexpensive tool for gender identification in
White-browed
Babblers.
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Abstract
Atalah, J., Anderson,
M.J. and
Costello, M.C. 2007. Temporal variability and intensity of grazing: a mesocosm experiment. Marine Ecology Progress
Series 341:
15-24.
Grazing has long been recognized as a
structuring force for
plant assemblages. Most of this knowledge comes from experiments where
grazers
have been excluded or their densities manipulated. However, the
intensity of
grazing can vary, in space and time. Recently, an increasing number of
studies
have stressed the importance of the variance around the mean of
ecological
processes, but the potential effects of temporal variability in grazing
in
marine systems have not yet been explored. Here, we examined the
separate
effects of intensity and temporal variability of gastropod grazing on
algal
assemblages in a mesocosm experiment. In
replicated
experiments, algal assemblages grown on artificial substrata were
subject to
grazing regimes with mean intensity and temporal variance as crossed
factors.
In the first experiment, the more variable regimes led to greater
reductions in
algal cover, regardless of the level of grazing intensity. In the
second
experiment, variability elicited a similar effect, but this effect was
larger
for the low- than for the high-intensity treatments. These results
indicate
that temporally variable grazing regimes may lead to greater effects on
algal
assemblages than those anticipated from changes in the mean intensity
of
grazing alone. Thus, we suggest that temporal variability is a
potentially
important aspect of grazing processes that should be examined and
incorporated
into predictive models.
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Abstract
Ford, R.B., Anderson,
M.J. and Kelly, S. 2007. Subtle and negligible effects of rainfall on
estuarine
infauna: evidence from three years of
event-driven
sampling. Marine Ecology Progress Series 340: 17-27.
Events of heavy rainfall can impact benthic
fauna in
estuaries. The occurrence of heavy rainfall is predicted to increase in
many
places due to climatic warming. It is therefore important to know the
likely
impact of events of heavy rainfall, both now and in the future,
particularly as
the discharge of some contaminants, such as sediments from large-scale
urban
developments, is correlated with such events. We tested for evidence of
any
impacts of rainfall on the structure of assemblages over a period of 3
years,
using event-driven sampling of macrofaunal
soft-sediment communities across 5 estuaries in the Auckland region. Changes in
assemblage
structure that was correlated with gradients in rainfall were detected
at only
2 of the 50 sites sampled. These site-specific impacts were only
detected in
one estuary and did not coincide with the largest amount of rainfall
measured
in the region over that period. Impacts were characterised
by a short-term increase in the number of taxa,
which
probably resulted from deposition of fauna transported with bedload
eroded from upstream sites due to increased flow rates. This contrasts
with
results from previous studies, which reported catastrophic decreases in
biodiversity or abundance with storm events. Our work provides a
realistic
baseline against which potential future impacts of rainfall associated
with
land development can be tested. We suggest long-term monitoring studies
that
incorporate measurements of relevant physical variables, including
rainfall,
are needed in order to more effectively assess significant changes in
naturally
temporally variable communities.
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Abstract
Terlizzi, A.,
Anderson, M.J., Fraschetti, S. and
Benedetti-Cecchi, L. 2007. Scales of spatial
variation in Mediterranean subtidal
sessile assemblages
at different depths. Marine Ecology Progress Series 332:
25-39.
Analyses of spatial patterns of distribution of
populations
and assemblages along environmental gradients are common in marine
ecology. How
these patterns vary at different spatial scales has seldom been
examined,
despite the fact that patterns in nature are intrinsically
scale-dependent.
This study quantified variability in subtidal
assemblages at a hierarchy of spatial scales along a depth gradient,
using
several univariate and multivariate
techniques.
Despite variation in the sizes of depth effects in time and space,
there were
large, significant and generally characterisable
differences in the structure of assemblages at different depths. The
sizes of
multivariate and univariate components of
variation
at different spatial scales were compared at each of 3 different depths
(5, 15
and 25 m), using a bias-corrected bootstrapping approach. The sizes of
variance
components at different spatial scales varied with depth and choice of
transformation.
In all cases, the largest component of variation was at the smallest
scale
(tens of centimeters). A pattern of decreasing residual variance with
depth was
seen for untransformed data, while a pattern of increasing residual
variance
with depth was seen for presence/absence data. In contrast, variation
among
locations (separated by >1 km) and among sites (separated by
hundreds of metres) was largest at
intermediate depths (~15 m),
regardless of the transformation used. The multivariate procedures used
here
offer several advantages over previously used techniques, providing
suitable
quantitative methods for analysing, at
multiple
scales, the patchy and complex nature of rocky subtidal
assemblages.
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Abstract
Langlois, T.J., Anderson, M.J. and Babcock, R.C. 2006. Inconsistent effects of
reefs on
different size classes of macrofauna in
adjacent sand
habitats. Journal of Experimental Marine Biology and Ecology
334:
269-282.
In soft-sediment communities near reefs, a
variety of
patterns have been described with distance from the reef edge. Various
studies
have observed contrasting patterns and one study has reported different
patterns for different size classes of macrofauna.
This study in northeastern New Zealand obtained
samples from 24 randomly
allocated sites across three locations in a large-scale mensurative
sampling design. At each location, there was a manipulation of
reef-associated
predator populations provided by established marine reserves. A
concurrent
study using the same sites found large macrofauna
(>4 mm) to vary with distance from the reef and relative to predator
density. The present study sampled small-bodied infauna
(<4 mm and >0.5 mm), which was also predicted to change with
distance
from the reef and predator density. In contrast to patterns found for
larger
fauna and to previous studies of small macrofauna,
no
consistent patterns were found for small-bodied infauna.
These results suggest that models of community structure need to
consider
different size classes of macrofauna
separately and
that multiple sampling methods will assist their investigation. The
‘haloes’ in small-bodied macrofauna
around reefs may not be as widespread or consistent as previous studies
have
suggested, particularly in mobile sediments on open coasts.
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Abstract
Anderson, M.J., Ellingsen,
K.E., McArdle, B.H. 2006. Multivariate dispersion as
a measure of
beta diversity. Ecology Letters 9: 683-693.
Beta diversity can be defined as the variability
in species
composition among sampling units for a given area. We propose that it
can be
measured as the average dissimilarity from individual observation units
to
their group centroid in multivariate
space, using an
appropriate dissimilarity measure. Differences in beta diversity among
different areas or groups of samples can be tested using this approach.
The
choice of transformation and dissimilarity measure has important
consequences
for interpreting results. For kelp holdfast assemblages from New Zealand,
variation in species composition was greater in smaller holdfasts,
while
variation in relative abundances was greater in larger holdasts.
Variation in community structure of Norwegian continental shelf macrobenthic fauna increased with increases in
environmental heterogeneity, regardless of the measure used. We propose
a new
dissimilarity measure which allows the relative weight placed on
changes in
composition vs. abundance to be specified explicitly.
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Abstract
Langlois, T.J., Anderson, M.J., Brock, M. and Murman, G. 2006.
Importance of rock lobster size-structure for trophic
interactions: choice of soft-sediment bivalve prey. Marine Biology
149: 447-454.
Ecologists are becoming increasingly interested
in how
variation in predator demographics influences prey communities. In
northeastern
New Zealand,
the contrasting populations of previously exploited predators in highly
protected marine reserves and fished areas have been used to
investigate the
effects of predation in soft-sediment habitats. However, these
experiments have
been unable to separate the role of predator size from that of density.
This
study provides evidence to support the model that foraging by different
sizes
of the rock lobster Jasus edwardsii affects soft-sediment bivalve
populations in
different ways. Feeding trials were conducted to investigate whether
rock
lobsters of different sizes vary in their choice of taxa
and size of their bivalve prey. Trials with two morphologically similar
species, Dosinia subrosea
and Dosinia anus, indicated
that
lobsters of all sizes choose D. subrosea
more
frequently than the heavier shelled D. anus. Further results
indicated
that both large (>130 mm carapace length (CL)) and small (<100 mm
CL)
lobsters are capable of preying on a wide size range of D. subrosea
(20–60 mm). However, small lobsters more frequently chose smaller
shells
(<30 mm) and large lobsters more frequently chose larger shells
(>40 mm).
Patterns in the abundance and size class distributions of these two
bivalve
species at protected and fished sites supported the feeding choices
observed in
the laboratory. These results suggest that populations of rock lobsters
with
large individuals inside reserves are capable of controlling the
demography of
bivalve populations in adjacent soft-sediment systems.
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Terlizzi, A., Scuderi,
D., Fraschetti, S. and Anderson, M.J. 2005. Quantifying effects of
pollution on
biodiversity: a case study of highly diverse molluscan
assemblages in the Mediterranean.
Marine
Biology 148: 293-305.
Structured sampling designs are important in the
assessment
of environmental impacts of variable ecological systems. Recent
developments
have provided a useful framework extending existing univariate
techniques into a multivariate context. Measures of taxonomic
relatedness have
also been introduced which complement existing measures of diversity of
assemblages. In this study, the potential effects of sewage discharge
on
spatial patterns of highly diverse molluscan
assemblages in a Mediterranean rocky subtidal
habitat
were investigated. Nine 20cm x 20cm quadrats
were
taken from each of 3 sites (80-100 m apart) within a putatively
impacted
location near a sewage outfall (I) and at each of two control
locations
(Cs) by destructive sampling by SCUBA divers at a depth of 3-4
m. A
total of 5507 specimens of 151 species were collected. The average and
the
variance in total abundance of molluscs
were greater,
on average, at I than at Cs.
Higher
abundances at the sewage outfall were largely driven by greater numbers
of
juvenile molluscs. The Shannon
diversity of molluscs (H') was
significantly lower at
I, but no difference among locations was detected for the
total number
of species (S). In addition, the taxonomic distinctness (∆*) of molluscs was greater at Cs, although it
was more
variable at I. Multivariate analyses showed that there was a
significant
difference in the structure of assemblages at I compared with Cs.
The location near the outfall was characterized by greater abundances
of
several species, including especially the gastropods Pusillina
philippi, Bittium latreilli
and B. reticulatum. There was also
greater
variability in the structure of assemblages among sites and among quadrats at control locations compared to those
near the
outfall. Using a suite of univariate
and multivariate measures, including diversity indices, detailed
information on
taxonomic structure and analyses of variability at different spatial
scales,
provided useful insights into the effects of sewage impacts on these
diverse
assemblages. These results also highlighted the importance of analysing measures of variance as well as mean
in
considering effects of stress in natural communities.
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Abstract
Watson, D.L., Harvey,
E.S., Anderson,
M.J. and
Kendrick, G.A. 2005. A comparison of temperate
reef fish
assemblages recorded by three underwater stereo-video techniques.
Marine
Biology 148: 415-425.
Three underwater stereo-video techniques were
used to sample
the relative densities and species richness of temperate reef fish
assemblages
at three reef locations and two habitats (high and low-relief reef)
within
Hamelin Bay, south-western Australia. The three techniques compared
were
diver-operated stereo-video strip transects, baited remote stereo-video
and unbaited remote stereo-video. While unbaited
remote stereo-video and diver operated stereo-video transects recorded
greater
species richness at high compared to low-relief reefs, baited remote
stereo-video recorded similar species richness at the two habitat
types. The
diver operated stereo-video system was manoeuvred
through caves and under overhangs recording small, cryptic,
cave-dwelling
species that were not recorded by either remote video technique (Trachinops noarlungae,
Trachinops brauni,
Chromis klunzingeri,
Trachichthys australis).
Both remote video techniques recorded greater species richness and
relative
density of the most common species of Labridae,
Ophthalmolepsis lineolatus.
Baited remote video recorded the rarer, large predatory fish species
(e.g. Seriola hippos, Glaucosoma
hebraicum, Heterodontus
portusjacksoni). None of the
techniques sampled
small cryptic fish families such as Gobiidae
or Blenniidae. A combination of survey
techniques is recommended
for comprehensive fishery-independent studies that aim to sample broad
components of fish assemblages.
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Abstract
Anderson, M.J. 2006.
Distance-based tests for homogeniety
of multivariate dispersions. Biometrics 62: 245-253
The traditional likelihood-based test for
differences in
multivariate dispersions is known to be sensitive to nonnormality.
It is also impossible to use when the number of variables exceeds the
number of
observations. Many biological and ecological data sets have many
variables, are
highly skewed, and are zero-inflated. The traditional test and even
some more
robust alternatives are also unreasonable in many contexts where
measures of
dispersion based on a non-Euclidean dissimilarity would be more
appropriate.
Distance-based tests of homogeneity of multivariate dispersions, which
can be
based on any dissimilarity measure of choice, are proposed here. They
rely on
the rotational invariance of either the multivariate centroid
or the spatial median to obtain measures of spread using principal
coordinate
axes. The tests are straightforward multivariate extensions of Levene’s test, with P-values obtained either
using
the traditional F-distribution or using permutation of either
least-squares or
LAD residuals. Examples illustrate the utility of the approach,
including the
analysis of stabilizing selection in sparrows, biodiversity of New Zealand
fish assemblages, and the response of Indonesian reef corals to an El
Niño. Monte Carlo simulations
from the real data sets show that
the distance-based tests are robust and powerful for relevant
alternative
hypotheses of real differences in spread.
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Abstract
Anderson,
M.J.,
Millar, R.B., Blom, W.M. and Diebel,
C.E. 2005. Nonlinear multivariate models of successional
change in community structure using the von Bertalanffy
curve. Oecologia 146:
279-286.
Von Bertalanffy curves were used to describe the
nonlinear
relationship between assemblages inhabiting holdfasts of the kelp, Ecklonia radiata,
and the volume of the holdfast. This was done using nonlinear canonical
analyses of principal coordinates (NCAP). The volume of the holdfast is
a proxy
for the age of the plant and, thus, the canonical axis is a proxy for
succession in the marine invertebrate community inhabiting the
holdfast.
Analyses were done at several different taxonomic resolutions on the
basis of
various dissimilarity measures. Assemblages in relatively large
holdfasts
demonstrated ongoing variation in community structure with increasing
volume
when the dissimilarity used was independent of sample size. Smaller
holdfasts
had proportionately greater abundances of ophiuroids
and encrusting organisms (bryozoans, sponges, ascidians) while larger
holdfasts
were characterized by proportionately greater abundances of
crustaceans, polychaetes and molluscs.
Such linear and nonlinear
multivariate models may be applied to analyse system-level responses to
the growth
of many habitat-forming organisms, such as sponges, coral reefs,
coralline
algal turf, or forest canopies.
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Abstract
Langlois, T.J., Anderson,
M.J. and Babcock, R.C. 2006.
Marine
reserves demonstrate trophic interactions
across
habitats. Oecologia 147: 134-142.
Several infaunal bivalve taxa
show
patterns of decreased biomass in areas with higher densities of
adjacent
reef-associated predators (the snapper, Pagrus
auratus and rock lobster, Jasus
edwardsii). A caging experiment was
used to test
the hypothesis that patterns observed were caused by predation, using
plots
seeded with a known initial density of the bivalve Dosinia
subrosea to estimate survivorship. The
caging
experiment was replicated at several sites inside and outside two
highly
protected marine reserves: predators are significantly more abundant
inside
these reserves. Survivorship in fully caged, partially caged and open
plots
were then compared at sites having either low (non reserve) or high
(reserve)
predator density. The highest rates of survivorship of the bivalve were
found
in caged plots inside reserves and in all treatments outside reserves.
However,
inside reserves, open and partially caged treatments exhibited low
survivorship. It was possible to specifically attribute much of this
mortality
to predation by large rock lobsters, due to distinctive marks on the
valves of
dead D. subrosea. This suggests
that predation
by large rock lobster could indeed account for the distributional
patterns
previously documented for certain bivalve populations. Our results
illustrate
that protection afforded by marine reserves is necessary to investigate
how
depletion through fishing pressure can change the role of upper-level
predators
and trophic processes between habitats.
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Abstract
Anderson, M.J., Diebel,
C.E., Blom, W.M and Landers, T.J. 2005. Consistency and variation in kelp holdfast
assemblages: spatial
patterns of biodiversity for the major phyla at different taxonomic
resolutions. Journal of Experimental Marine Biology and Ecology
320: 35-56.
The focus of this study was to measure natural spatial variability in
the
biodiversity of fauna inhabiting kelp holdfasts in northeastern New Zealand
at
several spatial scales: from meters up to hundreds of kilometers. We
wished to
test the hypothesis that multivariate variation and biodiversity would
vary
significantly at different spatial scales in different ways for the
major phyla
in the holdfast community (Arthropoda, Annelida, Mollusca
and Bryozoa). Biodiversity was considered
in terms of richness,
total abundance, structural composition (as measured by the Bray-Curtis
dissimilarity measure) and taxonomic breadth for each major phylum and
for the
assemblage as a whole. We also examined the effect of taxonomic
resolution on
multivariate patterns. Species richness and total abundance increased
with
increases in holdfast volume. Multivariate variation was greatest at
the
smallest spatial scale for all phyla, but different phyla showed
different
patterns of multivariate variation at different spatial scales.
Variations
among locations at the largest spatial scale were primarily due to
differences
in the composition and richness of bryozoans and molluscs.
Location effects became less and less distinct with decreases in
taxonomic
resolution. There were very few significant differences in richness or
abundance for holdfasts of a given volume, taxonomic breadth did not
vary
significantly across locations, nor did the proportional abundances of
phyla.
These consistencies across large spatial scales in the absence of
environmental
impacts and results from other studies suggest that holdfast
communities in New
Zealand
systems would provide a useful model assemblage against which future
impacts
may be detected as changes in proportions of component phyla. In
addition, high
variability detected at small and large scales at the species level,
especially
for bryozoans and molluscs, suggest that
these
communities may also provide unique opportunities for studying and
understanding sources and functions of marine biodiversity.
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Abstract
Anderson, M.J., Connell, S.D.,
Gillanders, B.M., Diebel,
C.E., Blom, W.M., Landers, T.J. and
Saunders, J.E.
2005. Relationships
between taxonomic resolution and spatial scales of multivariate
variation in
kelp holdfast assemblages. Journal of Animal Ecology 74: 636-646.
Summary
1. We
investigated the
effects of changes in taxonomic resolution on analyses of patterns of
multivariate variation at different spatial scales for the highly
diverse fauna
inhabiting holdfasts of the kelp Ecklonia radiata.
2. Multivariate analyses were done using several transformations
to
examine differences in spatial patterns of variation from meters up to
hundreds
of kilometers for composition versus relative abundance in assemblages.
3. The greatest variability in assemblages occurred at the
smallest
spatial scale, from plant to plant, pointing to the existence of
important
small-scale processes. The proportional amount of variation at the
smallest
spatial scale decreased with decreasing taxonomic resolution (i.e.,
from
species through to phyla). For composition, the next-greatest source of
variation was at the largest spatial scale (hundreds of kilometers),
while for
relative abundance, the next-greatest source of variation was at the
level of
sites (hundreds of meters to kilometers).
4. For abundance data, location-level variation became less
important and
site-level variation became more important with decreasing taxonomic
resolution, while for compositional data, the opposite pattern
occurred. This
suggests that variation in the presence of species or taxa
at a particular location along the coast is driven by large-scale
processes,
while variation in relative abundances within locations is driven by
medium-scale processes.
5. The lack of significant variation in the proportional
abundances of
phyla at large spatial scales suggests that some consistency of pattern
may
emerge at larger scales (spatial and/or taxonomic), even in the
presence of high
small-scale variability. These findings strengthen the idea that
substantial
local variation need not preclude the existence of broad-scale
organization in
ecological patterns and biodiversity.
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Abstract
Millar, R.B., Anderson,
M.J. and Zunun, G. 2005. Fitting nonlinear
environmental
gradients to community data: a general distance-based approach. Ecology
86: 2245-2251.
A distance-based method is provided for the analysis and modeling of
multivariate community data in response to a nonlinear gradient. Any
reasonable
dissimilarity measure can be used, and the method provides a natural
extension
from canonical analysis of principal coordinates (CAP) to nonlinear
canonical
analysis through the use of a link function, much like the extension of
linear
models to generalized linear models. The form of the nonlinear link
function
needs to be specified and will depend on the particular ecological
system and
the nature of the gradient. For example, an exponential decay curve
could be
used to model community structure after an environmental impact as a
nonlinear
function of time. This curve is used in our first example, where
community
structure is modeled as a nonlinear function of habitat size. Our
second
example uses a logistic curve to model change in community structure
through a
region of habitat transition from grassland to woodland.
Computationally, this
methodology uses a standard nonlinear optimization procedure to find
the values
of the parameters that maximize the correlation of the principal
coordinates
(obtained from an appropriately chosen distance measure) with the
chosen form
of nonlinear gradient. A simple randomization procedure is used to test
the
significance of the fitted nonlinear gradient over and above the fit of
the
linear gradient, and bootstrap confidence intervals for parameters are
readily
obtained. Any reasonable form of nonlinear gradient can be used, and it
can be
modeled as a nonlinear function of multiple environmental variables,
making
this a very flexible and versatile procedure for modeling multivariate
ecological systems.
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Abstract
Langlois, T.J., Anderson,
M.J. and Babcock, R.C. 2005.
Reef-associated predators influence adjacent soft-sediment communities.
Ecology
86: 1508-1519.
Marine reserves provide a large-scale manipulation of predator
densities, which
provides a means to investigate the potential effects of predation. The
effects
of reef-associated predators were examined in northeastern New Zealand
by
comparing soft-sediment assemblages at sites having different densities
of
large predators. Large rock lobsters (Jasus
edwardsii) were 3.8 times more abundant
and large
snapper (Pagrus auratus)
12 times more abundant, on average, at reserve sites compared with
non-reserve
sites. The overall structure of infaunal
communities
differed between areas with high predator densities (reserve) and those
with
lower densities (fished). Sites with consistently higher densities of
snapper
and lobster were found to have lower biomass of two bivalve species and
the
greatest decreases were found near the reef edge (2-5 m). For several
fauna a
strong gradient in their density with distance from the reef was
observed at
both reserve and non-reserve sites. The hermit crab Pagurus
novizelandiae occurred more frequently
near the
reef edge, whilst the heart urchin Echinocardium
cordatum and bivalve Dosinia
subrosea occurred more frequently
further away
from the reef. The results suggest that certain species in this
assemblage are
affected differently by a combination of physical and biological
forces. We
concluded that, where reef predators are removed by fishing pressure, a
resultant indirect effect is an increase in prey species in adjacent
soft-sediment assemblages.
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Abstract
Millar, R.B. and Anderson,
M.J. 2004. Remedies
for pseudoreplication. Fisheries
Research
70: 397-407
Pseudoreplication is the failure of a
statistical
analysis to properly incorporate the true structure of randomness
present in
the data. It has been well documented and studied in the ecological
literature
but has received little attention in the fisheries literature. Avoiding
pseudoreplication in analyses of fisheries
data can be
difficult due to the complexity of the statistical procedures required.
However, recent developments in statistical methodology are decreasing
the
extent to which pseudoreplication has to
be
tolerated. Seven examples are given here, beginning with simple
design-based
remedies and progressing to more challenging examples including the
model-based
remedies of mixed-effects modelling,
generalized
linear mixed models, state-space models, and geostatistics.
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Abstract
Hewitt, J.E., Anderson, M.J.
and Thrush, S.F. 2005.
Assessing and monitoring ecological community health in
marine systems. Ecological Applications 15:
942-953.
The increased potential for long-term degradative
change associated with large-scale diffuse impacts highlights the need
to
develop methods for assessing the ecological significance of any
observed
changes. The approach used in this study defines relative
“health” based on the range of communities present in locations not
considered affected by anthropogenically-derived
inputs. Such a definition should serve to identify both acute
effects and
broader-scale degradation. Three multivariate
constrained-ordination
techniques were used to assess changes in communities occurring along
an anthropogenic
disturbance gradient of storm-water pollution in two different
habitats.
All three techniques detected changes, even with data sets that were
not
specifically designed for the purpose. Comparison with five
diversity
indices suggested that the multivariate approach was more
successful.
Moreover, the information could easily be examined for changes in
individual
species, or for changes in function, trophic
status
or biomass/size structure. The approach allows for monitoring
changes
over time in community composition to determine whether sites are
improving or
degrading. While this study occurred in one region only, the
approach
itself is not confined to this area and should be able to be utilised in other marine (or freshwater or
terrestrial) systems
where commensurable regional-scale multivariate databases exist.
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Abstract
Terlizzi, A., Benedetti-Cecchi,
L., Bevilacqua, S., Fraschetti,
S., Guidetti, P. and Anderson, M.J. 2005.
Multivariate and univariate asymmetrical
analyses in
environmental impact assessment: a case study of Mediterranean subtidal sessile assemblages. Marine Ecology
Progress
Series 289: 27-42.
Characterizing the potential effects of human activities on natural
systems is
a central problem in applied ecology. This requires the development of
analytical procedures able to separate human perturbation from natural spatio-temporal variability displayed by most
populations.
Beyond-BACI experimental designs provide a framework to address these
issues
but, to date, their use is limited to the
analysis of
human impacts on the abundance of single species or other univariate
measures. Here, we describe in detail an asymmetrical design that
included 1
impact location (I) and a set of 3 controls (Cs), sampled at a
hierarchy of
spatial scales 4 times over a period of 15 mo. We focused on shallow subtidal assemblages of sessile organisms
exposed to sewage
discharge along a stretch of coast in southern Italy.
The purpose of this paper is
to illustrate (1) the comparison of variance components for the
assessment of
impacts and (2) the use of recently developed multivariate methods
(distance-based premutational MANOVA) in
the analysis
of multivariate species data in response to a complex asymmetrical
design.
Results indicated that temporal changes in the whole assemblage at I
were
distinct from those occurring at Cs, and that the nature of this
difference
(although not its size) was fairly consistent through time. A suite of taxa was identified as important in
characterizing the
differences found between I and Cs. Some
algae (e.g. Colpomenia sinuosa,
Gelidium sp. and Pterocladiella
sp.), in particular, occurred uniquely at I. Univariate
analyses indicated significant Time × I-v-Cs interactions for
several taxa, and significantly smaller
spatial variation at the
scale of quadrats at I compared to Cs. In
contrast,
the small-scale spatial variation in the number of taxa
was significantly greater at I than at Cs.
The
findings of this study have important implications for future
multivariate and univariate analyses in
environmental impact assessment.
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Abstract
Geffen, E., Anderson,
M.J. and Wayne, R.K. 2004. Climate and habitat barriers to dispersal in the highly
mobile gray
wolf. Molecular Ecology 13:
2481-2490.