Exam 3 Vocab Flashcards
bisect
a scale drawing of the vegetation along a transect—time-consuming, typically not done when looking at many different plots
phanerophytes
trees (buds high above ground)
Chamaephytes
shrubs
Hemicryptophytes
grasses
Cryptophytes
perennial forbs
species richness
number of species in the community
evenness
extent to which spp in community are equally abundant
Species frequency
Percentage of quadrats (plots) in which species occurs (Inaccurate for rare or spatially clumped species; Uninformative for very common species)
Species cover
Percentage of the ground covered by a given species (can use Basal cover or Basal area; Canopy cover)
Density (e.g., stem density)
Number of individuals of a species per unit area
Species importance value
Relative cover + Relative density + Relative frequency
Species biomass
Requires destructive sampling/weighing in the lab, or calculations based on detailed field allometric measurements (never as accurate as weighing)
Univariate statistics
compare spp abundance among communities (using a single dependent variable)
-can help to see environmental factors/site history changes altering spp composition
Multivariate statistics
compare spp composition among communities–comparing different spp and communities to each other (using multiple dependent variables)
-can graph as triangles to measure dissimilarity in terms of Euclidean distance (Pythagorean theorem)
Similarity Indices
used to measure differences among communities
-presence/absence indices bt 2 sites: (# of spp—many options; Jaccard index, etc)
-abundance indices: use abundance of individual spp (% similarity, Bray-Curtis index, etc)
-reducing dimensionality of data using ordination (N spp = N dimensions for similarity calculations)
-can collapse data (from many diff spp) into 2-3 dimensions to help better visualize compositional differences among plots; and to identify the major gradients in composition (whether spp related linearly or not—line of best fit)
Ordination—aka indirect gradient analysis
-the stands are ordered by their similarity in species composition and the environmental factors responsible for the resulting patterns are inferred
– requires predetermining which environmental factors are important first
–tends to be biased toward factors that can be easily measured
–patterns imposed by biotic interactions (e.g., competition, herbivory) are ignored
EX: looking at woody composition in a tropical dry forest
-step 1: samples ordered by similarity in spp composition
-step 2: look for envr factors responsible for variation
Direct gradient analysis
-DEVELOPED BY ROBERT WHITTAKER
–the ecologist chooses environmental axes and orders vegetation samples (stands) along those axes, examining the resulting patterns *uses compositional differences to infer environmental & other gradients from species compositional changes
–can include a large number of environmental factors
–includes biotic interactions & site history
EX: looking at 63 lodgepole pine stands in the Canadian Rockies along 2 gradients (moisture & elevation)
-step 1: order samples along a few known envr gradients (ex: Jasper & Banff 63 lodgepole stands in Canada—Whittaker)
-Step 2-cluster data until certain rules are met (to make it more reasonable number of clustered communities
-step 3: relate community comp to known envr gradients & use supplemental statistics
Rarefaction
to standardize to a common number of individuals or samples
Euclidean distance
The measure of the difference between each pair of communities
dimension reduction
taking highly multivariate data and collapsing them into a small number of dimensions
multiple regression
This technique determines the relationship of the abundance of our species to each environmental variable while correcting for correlations among the environmental variables themselves
indicator species
An ideal indicator species is found in all communities of a given type and not in any other community type. The use of indicator species makes classification of communities much easier.
ground-truthing operations
in which randomly selected sites are surveyed to see whether their actual species composition matches that predicted by the remote sensing classification.
Plant Succession
directional change in community structure or composition over time
Climax Community
communities in equilibrium with their environment
Progressive Succession
diversity & biomass increase over time, envr chgs toward mesic conditions
Retrogressive succession
diversity & biomass decrease over time, environment change to more extremes (hydric or xeric)
Autogenic succession
change in community composition driven by organisms themselves (increased shading by canopy trees, more nutrients by N-fixers/leaf litter)
Allogenic succession
change in community caused by external forces, not organisms (climate chg etc)
Relay Floristics Theory of Succession
idea was groups of spp gradually change to replace each other (like in a relay race)—earlier spp facilitate establishment/growth of later spp *Clementsian
Initial Floristic Composition Theory of Succession (Egler 1954)
all spp present at beginning—spp change in abundance based on life histories/how they express themselves in community (ex: trees take longer) *Gleasonian
Monoclimax or Climatic Climax Theory
(Clements 1916): only one uniform climax plant community type determined solely by climate. Succession modifies envr to overcome envr conditions
Polyclimax Theory
(Tansley 1935) climax veg of a region consists of more than 1 vegetation climax controlled by soil moisture, nutrients, topography, slope aspect, fire, animals activity, etc
Climax Pattern Theory
(Whittaker 1953) variety of climaxes governed by responses of spp pops to biotic and abiotic conditions. (envr determines plant composition of climax by affecting spp responses to these factors as well as propagule availability in space and time, disturbance. Climax vegetation can change as envr changes.
Alternative Stable States Theory
plant communities can exist in multiple “stables states”. Each is represented by a unique combo of biotic and abiotic conditions. Alternative stable states may transition from one to the another.
—ecological feedback mean communities display resistance to state shifts, or multiple state may persist under equal envr conditions (hysteresis)
–closer to current understanding—we have complex system behaviors, stochastic processes dominate, succession is unpredictable
Patch Dynamics
plant community as a dynamic mosaic of patches
Ex: Watt (1947) looked at distribution of heather, bearberry, lichen, & bare soil in Scottish moors—found that there were alternating strips of each, pointing against Clementsian theory of succession—more individualistic due to conditions & competition
-spp respond to spatial or temporal variation, stochastic models influenced by chance events, nonlinear dynamics with multiple equilibrium points
Lottery Model
Lottery models assume that many species are competing simultaneously, so the competition between any particular pair of species is fairly weak. If some species are very similar to one another, they may compete much more strongly.
looks at spatial & temporal variation in environment & thus in spp coexistence. Diffuse asymmetric competition between different spp. Stochasticity in mortality & recruitment (first-come, first-served)
-has disperser pool and models competition between juveniles, looks at adult age/life span; stochastic event probabilities, etc (ex: Forest Gap models)
species pool
the species available for colonization
dendrochronology
the study of tree rings
surface fire
runs along the soil surface or ground vegetation and destroys only herbaceous plants or low-growing shrubs
crown fire
spreads from the canopy of one tree to another, killing most of the canopy trees as well as most of the shrubs and other vegetation
fuel load
the amount of combustible plant material (living and dead) in the community.
Pyrogenic
that is, their accumulated leaf or twig litter tends to promote fire more than one would expect based on the mass of the litter alone.
Windthrows
range from blowdowns of branches or large parts of trees to losses of single trees and neighboring groups of trees.
cryptogamic crust
a thin layer of mosses, fungi, various unicellular photosynthetic organisms, lichens, and cyanobacteria
serotiny
in which they retain their seeds in tightly sealed cones for many years, releasing them only after exposure to fire
safe site
a favorable spot for their germination and growth
hysteresis
when simply reversing or eliminating the cause of a change may not cause the system to quickly return to its previous state
Seral communities
preclimax communities
storage effect
The reproductive potential of each population is “stored” between generations ex: if one spp can only reproduce during warm & wet conditions, only certain generations/populations/even individuals with right conditions may have high reproductive potential
Resistance
ability to weather disturbance without change
Resilience
rate of recovery after disturbance
Constancy (Tilman)
degree of temporal stability
Paradox of Enrichment
diversity frequently tends to decline in highly productive envr (also changes in density, size of individuals, and/or composition)
–lots of variability, often hump-shaped (lowest productivity with medium diversity), sometimes positive
–different patterns can be observed in large-scale experiments than at small-scale due to differing factors among plant communities (envr factors, available resources, spp composition, site history/successional age, etc) *Loreau (2000)
Niche Differentiation Effect
more spp better exploits available resources (aka niche partitioning effect/complementarity effect)
-more spp = many different factors and niches filled, so more likely that spp present will be able to use resources more fully (fewer unexploited habitat/resources)
Sampling Effect
productive spp are more likely to be present at high diversity (aka selection effect)—can lead to paradox of enrichment
-more diversity = better competitors (with greater productivity), this causes dominance by the best competitors (therefore potentially lower overall diversity/spp richness of community)
-depends on size and random factors in choosing species/communities sampled
Portfolio Effect
summed variation across many spp is less than variation of any individual spp—community variability decreases w added spp
-each spp varies from each other (individualistic Gleasonian responses)—community variation will decline
Negative Covariance Effect
spp with niche overlaps compete—thus when 1 spp declines the other can increase (aka competitive compensation)
—negative correlation between these spp
Overyielding Effect
biomass of each spp declines proportionately to diversity/richness as the total community biomass is divided amongst more spp
–spp biomass decline is oftentimes disproportionate amongst spp with increasing spp richness—but there can be underyielding or overyielding spp within the community (doing either worse or better than expected in models)
-more productive spp are more likely to over-yield (ex: C4 grasses or N-fixers)
intermediate disturbance hypothesis
species diversity should be highest at intermediate levels of disturbance
Abundance curves
compare spp abundance across different plant communities
-ranks spp from most to least abundant -most common to left of graph (most abundant is ranked as 1); uncommon to right -can help to predict abundancy in certain ecosystems without actual surveying *may suggest competitive hierarchy---but testing needs to rule out other causes
Trade-off
efficiency of exploiting a particular niche vs niche breadth
Theory—high specialization should cause rarity elsewhere (outside of specific niche)
-local abundance should be neg correlated with # of occupied habitats
Bounded Ranges Hypothesis (Null Model)
species ranges are bounded by geometric constraints
-latitudinal—spp bounded by N & S poles—more spp at equator where ranges freely overlap
-longitudinal—spp ranges bounded by coasts—more spp mid-continent where ranges overlap
-elevational gradient—spp ranges bounded by mountaintops and deserts at low elevation—more spp in mid-elevations
Ecological Equivalency
Phylogenetically unrelated species that occupy similar habitats (environmental conditions) in different parts of the world resemble each other due to convergent evolution. These species can become invaders outside of their native ranges in environmental conditions that they evolved in (cf. the same climate zones in different parts of the world).
Biotic resistance
more diverse communities consume more resources, leave less available to potential invaders (due to local factors – niche relations, other?)
Spatial pattern
Non-random, repetitive organization in space
Spatial process
Mechanism that causes spatial patterns
metapopulation theory
The population size of a species on any given island is a result of local population dynamics plus immigration minus emigration
