Fortin MJ, Keitt TH, Maurer BA, Taper ML, Kaufman DM, Blackburn TM. Species' geographic ranges and distributional limits: pattern analysis and statistical issues. OIKOS. 108 :7–17.Abstract
With the increasing concern about species conservation, a need exists for quantitaive characterization of species' geographic range and their borders. In this paper, we survey tools appropriate for the quantification of static spatial patterns related to geographical ranges and their borders. We then build on these static methods to consider the problem of changes in geographic range through time. Methods discussed are illustrated using lark sparrow data from the North American Breeding Bird Survey. While there is no such thing as the ``best\''\ or ``only\''\ method to analyze species geographical range and border, we show that a series of methods can be used in sequence to provide complementary and useful quantitative information for species occupancy of range. Indeed, the location of species' borders estimated at different times can be compared to identify locations where species expand or go locally extinct. The ability to delineate accurately species' ranges will be useful to conservation biologists, managers and ecologists.
Holt RD, Keitt TH, Lewis MA, Maurer BA, Taper ML. Theoretical models of species’ borders: single species approaches. Oikos [Internet]. 108 :18–27. Publisher's Version
Keitt TH. Network theory: an evolving approach to landscape conservation. In: Dale VH Ecological Modeling for Resource Management. New York: Springer ; pp. 125–134. Publisher's Version
Brown MT, McMahan EA, Mitsch WJ, Diamond C, Winasrky I, Chandler R, Carstenn S, McLachlan-Karr J, Nixon S, Tilley DR, et al. Prof. Howard T. Odum 1924-2002. ENERGY. 28 :293–301.
Keitt TH. Spatial autocorrelation, dispersal and the maintenance of source-sink populations. ECOLOGICAL STUDIES. :225–238.
Keitt TH, Bjornstad ON, Dixon PM, Citron-Pousty S. Accounting for spatial pattern when modeling organism-environment interactions. Ecography. 25 :616–625.Abstract
Statistical models of environment-abundance relationships may be influenced by spatial autocorrelation in abundance, environmental variables, or both, Failure to account for spatial autocorrelation can lead to incorrect conclusions regarding both the absolute and relative importance of environmental variables as determinants of abundance. We consider several classes of statistical models that are appropriate for modeling environment-abundance relationships in the presence of spatial autocorrelation, and apply these to three case studies: 1) abundance of voles in relation to habitat characteristics; 2) a plant competition experiment; and 3) abundance of Orbatid mites along environmental gradients. We find that when spatial pattern is accounted for in the modeling process, conclusions about environmental control over abundance can change dramatically. We conclude with five lessons: 1) spatial models are easy to calculate with several of the most common statistical packages; 2) results from spatially-structured models may point to conclusions radically different from those suggested by a spatially independent model; 3) not all spatial autocorrelation in abundances results from spatial population dynamics; it may also result from abundance associations with environmental variables not included in the model; 4) the different spatial models do have different mechanistic interpretations in terms of ecological processes - thus ecological model selection should take primacy over statistical model selection; 5) the conclusions of the different spatial models are typically fairly similar - making any correction is more important than quibbling about which correction to make.
Keitt TH, Amaral LAN, Buldyrev SV, Stanley HE. Scaling in the growth of geographically subdivided populations: invariant patterns from a continent-wide biological survey. Phil. Trans. R. Soc. Lond. B. 357 :627–633.
Keitt TH, Lewis MA, Holt RD. Allee Effects, Invasion Pinning, and Species' Borders. The American Naturalist. 157 :203–216.
Urban D, Keitt T. Landscape connectivity: a graph-theoretic perspective. Ecology [Internet]. 82 :1205–1218. Publisher's Version
Kendall BE, Bjornstad ON, Bascompte J, Keitt TH, Fagan WF. Dispersal, environmental correlation, and spatial synchrony in population dynamics. The American Naturalist. 155 :628–636.
Bunn A, Urban DL, Keitt TH. Landscape connectivity: A conservation application of graph theory. Journal of Environmental Management [Internet]. 59 :265–278. Publisher's Version
STANLEY H, AMARAL L, Gopikrishnan P, IVANOV P, Keitt T, Plerou V. Scale invariance and universality: organizing principles in complex systems. Physica A: Statistical Mechanics and its Applications [Internet]. 281 :60–68. Publisher's Version
Keitt TH. Spectral representation of neutral landscapes. Landscape Ecology [Internet]. 15 :479–494. Publisher's Version
Holt RD, Keitt TH. Alternative causes for range limits: a metapopulation perspective. Ecology Letters [Internet]. 3 :41–47. Publisher's Version j.1461-0248.2000.00116.x.pdf
Micheli F, Cottingham KL, Bascompte J, Bjornstad ON, Eckert GL, Fischer JM, Keitt TH, Kendall BE, Klug JL, Rusak JA. The dual nature of community variability. Oikos [Internet]. 85 :161––169. Publisher's Version
Keitt THTH, Stanley HE. Dynamics of North American breeding bird populations. Nature [Internet]. 393 :257–260. Publisher's Version
Keitt TH. Stability and complexity on a lattice: coexistence of species in an individual-based food web model. ECOLOGICAL MODELLING. 102 :243–258.Abstract
Theoretical studies of the stability of food webs have generally not incorporated space as a contingency affecting coexistence of species. Here, I considered the importance of spatial heterogeneity on the stability of an individual-based food web model. Individual agents diffused on a lattice of cells and interacted according to a set of probabilistic interaction coefficients. Simulations were run on both uniform and non-uniform lattices. The model had two modes: 1. a mean-field mode with global interactions, and 2. a spatially localized mode in which species interacted within local neighborhoods. Equilibrium number of species were compared among different simulations varying web connectance, interaction strength, and lattice heterogeneity. Local interactions resulted in more species rich webs, indicating greater stability. The addition of spatial heterogeneity to the lattice further altered relationships among species richness, web connectance, and interaction strength, and increased coexistence among species. The results did not support the stability criterion derived by May. However, an inverse relationship between web connectance and species richness was observed suggesting that the product of connectance and species richness may govern the stability of real, finite webs. (C) 1997 Elsevier Science B.V.
Keitt TH. Population dynamics in ecological space and time. Complexity. 3 :58.
Keitt TH, Urban DL, Milne BT. Detecting Critical Scales in Fragmented Landscapes. Conservation Ecology. 1 :4. conservation_ecology-_detecting_critical_scales_in_fragmented_landscapes.pdf
Milne BT, Johnson AR, Keitt TH, Hatfield CA, David J, Hraber PT. Detection of critical densities associated with pinon-juniper woodland ecotones. ECOLOGY. 77 :805–821.Abstract
The interfaces between pifion-juniper canopies and grasslands in the southwestern USA present an opportunity to use the modern theory of spatial phase transitions as a formal characterization of ecotone structure. The theory requires an estimation of a critical value of tree cover at which the woodlands switch abruptly from a fragmented collection of small patches of trees to a network of connected canopies. Presumably, this transition is associated with critical environmental conditions that regulate the ecologies of trees vs. grasses. We developed and tested a new method to estimate the critical cover value of woodlands on complex terrain. The method was based on multiscale assessments of the associations between local tree coverage and two types of patch edge. Tests on artificial gradient percolation maps revealed an interaction between the type of edge used (''hull edge,'' which is based on only the orthogonal connections between canopy-occupied cells, vs. `'accessible edge,'' which is based on both orthogonal and diagonal connections beween canopy-occupied cells) and the neighborhood rule used to define a cluster (von Neumann 5-cell or Moore 9-cell). When applied to digitized, geographically referenced aerial photographs, the method indicated that areas less than or equal to 6.6 ha exhibited the theoretical critical value of 59.3% cover predicted for square lattices and the 5-cell neighborhood. Construction of both edge types on a given map can reveal locations of steep environmental gradients that may be buffered against modest climate fluctuations. The edges can be used in the calibration of independent variables to predict tree cover. The agreement between the expected and observed critical densities will motivate extensions of phase transition theory to studies of ecotones in real landscapes.