Initial Floristic Composition Hypothesis Statement

Citation: Laurance WF, Nascimento HEM, Laurance SG, Andrade A, Ewers RM, Harms KE, et al. (2007) Habitat Fragmentation, Variable Edge Effects, and the Landscape-Divergence Hypothesis. PLoS ONE 2(10): e1017. https://doi.org/10.1371/journal.pone.0001017

Academic Editor: Peter Bennett, University of Kent, United Kingdom

Received: July 12, 2007; Accepted: September 21, 2007; Published: October 10, 2007

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

Funding: Support was provided by the U.S. National Science Foundation, NASA-LBA Program, A. W. Mellon Foundation, Conservation, Food and Health Foundation, World Wildlife Fund-U.S., MacArthur Foundation, National Institute for Amazonian Research, and Smithsonian Institution.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Habitat fragmentation is among the most important of all threats to global biodiversity [1], [2], and edge effects—diverse physical and biotic alterations associated with the artificial boundaries of fragments—are dominant drivers of change in many fragmented landscapes [2]–[10]. Edge effects can have serious impacts on species diversity and composition, community dynamics, and ecosystem functioning [11]–[17].

Many edge effects are variable in space and time [7], [9], [18]–[21]. Of course, the strength of edge effects diminishes as one moves deeper inside forests, but in addition, many edge phenomena vary markedly even within the same habitat fragment or landscape. Factors that might promote edge-effect variability include the age of habitat edges [22]–[25], edge aspect [26], [27], the combined effects of multiple nearby edges [28]–[31], fragment size [10], the structure of the adjoining matrix vegetation [32]–[34], seasonality [35], influxes of animals or plant propagules from surrounding degraded lands [9], [36]–[38], extreme weather events [39], [40], and fires [41], [42].

In the Brazilian Amazon, up to 50,000 km of new forest edge is being created annually [43] as a result of rapid clearing and fragmentation of forests for cattle ranching, soy production, slash-and-burn farming, industrial logging, and wildfires [44]–[47]. For nearly three decades, we and our colleagues have studied edge effects in Amazonian forests as part of the world's largest and longest-running experimental study of habitat fragmentation [e.g. 5], [ 13]–[15], [ 17]–[19], [ 23], [ 24], [ 27]–[30], [ 32], [ 36], [ 38]–[41], [ 48]–[61](Figure 1). Here we evaluate factors that instigate variability in edge phenomena, focusing on ten edge-related changes in forest dynamics, plant community composition, invasive species, and carbon storage. Our findings prompt us to present a new hypothesis about the behavior of fragmented ecosystems that, if valid, will have key implications for biodiversity conservation.

Figure 1. Study area in central Amazonia.

Shaded blocks indicate locations of forest fragments and intact-forest controls used in the study. Stippled areas are cattle pastures or regrowth forest, while unstippled areas are intact forest. Thick, solid lines are roads.

https://doi.org/10.1371/journal.pone.0001017.g001

Results

Variability in edge effects

Most of the edge-effect variables we evaluated (see Methods) exhibited pronounced spatial and temporal variability. For example, two of the most ecologically important parameters, the overall rates of tree mortality and recruitment, were spatially much more variable near forest edges (plot center<100 m from edge) than in forest interiors (>100 m from edge). Using standard deviations (SDs), among-plot variability was dramatically elevated for both mean mortality (F32,32 = 3.29, P = 0.0006) and recruitment (F32,32 = 8.13, P<0.0001; F-tests). These differences did not simply result from higher mean mortality and recruitment rates near edges (Figure S1), because coefficients of variation (CV), which adjust for differences in mean values, were also elevated near edges (mortality: 40.5% vs. 34.1%; recruitment: 47.9% vs. 27.9%).

Tree mortality and recruitment rates were also temporally far more variable near edges. When among-census variation was quantified for each plot using SDs (Figure 2A), values for both mortality (rs = −0.440, P = 0.0002) and recruitment (rs = −0.670, P<0.00001) were sharply elevated near edges (Spearman rank correlations). CVs for mortality and recruitment also rose markedly nearer fragment margins (Figure 2B), indicating that both were temporally hyper-variable near edges.

Figure 2. Pronounced temporal variability of tree mortality and recruitment rates near Amazonian forest edges.

This variability is measured by (A) standard deviations and (B) coefficients of variation of among-census variation for 1-ha plots. In (B), the solid regression line is for mortality (F1,64 = 5.68, R2 = 8.2%, P = 0.02) and the dashed line for recruitment (F1,64 = 27.30, R2 = 29.9%, P<0.0001).

https://doi.org/10.1371/journal.pone.0001017.g002

Most other edge parameters exhibited similar trends. On average, tree densities fluctuated more dramatically over time near forest edges than in interiors (P = 0.0023, Mann-Whitney U-test), and these fluctuations were more spatially variable near edges (F32,32 = 8.14, P<0.00001; F-test based on variances in CV values). Likewise, edge plots had sharply elevated spatial variability in overall tree-community change (F18,20 = 17.76, P<0.0001), floristic trajectories 1 and 2 (both F18,20>9.08, P<0.0001), the abundance of pioneer and invasive trees (F32,32 = 11.59, P<0.00001), and tree-species turnover (F18,20 = 15.25, P<0.0001), relative to forest interiors (all F-tests comparing variances in edge vs. interior plots). Only liana abundance (F32,32 = 1.35, P = 0.20) and the average rate of biomass change (F32,32 = 1.19, P = 0.31) did not increase in spatial variability on edges relative to interiors, and even these had somewhat (17–19%) higher SDs on edges.

Predictors of variability

Three variables, cattle ranch, distance to forest edge, and the number of nearby edges, were the most important predictors of spatial variation in edge phenomena, having significant effects on six, five, and two edge-effect variables, respectively (Table 1). Analyses explained 38–60% of the total variation in edge variables. As expected, edge phenomena increased in intensity closer to forest edges and with more nearby edges. In pairwise comparisons among the three cattle ranches, tree mortality and recruitment, fluctuations in tree abundance, and the abundance of pioneer and invasive trees were all significantly (P<0.05) higher in fragments at Dimona than Esteio, with Porto Alegre being intermediate (Porto Alegre also had significantly higher recruitment than Esteio; Tukey's tests). Soil factors, slope, and fragment area per se had no significant influence on edge-effect variables.

Spatial and temporal variability in tree mortality evidently helps to drive variability in several other edge-effect phenomena. First, in simple (Bonferroni-corrected) correlations among the edge and predictor variables, tree mortality was strongly (r>0.60, P<0.00001) correlated with all other edge-effect parameters except liana abundance (Table S1). Second, when the GLM analyses were repeated but with tree mortality included as a potential predictor, model performance improved (explaining 42–91% of the variation in edge parameters) and tree mortality was a significant predictor for all edge variables except liana abundance (Table S2). Model improvement was greatest for four floristic variables (overall change in tree-community composition, floristic vectors 1 and 2, and the rate of tree-species turnover). Finally, for several edge-effect variables, such as floristic vector 2 (Figure 3A) and tree-species turnover (Figure 3B), tree mortality was a highly significant covariate when the variables were contrasted among cattle ranches.

Figure 3. Ecological differences among forest fragments in three Amazonian cattle ranches.

Differences among the ranches are shown for (A) floristic change (floristic vector 2) and (B) tree-species turnover, using the mean tree-mortality rate in each plot as a covariate.

https://doi.org/10.1371/journal.pone.0001017.g003

Given the apparently important impacts of tree mortality on forest ecology, we evaluated how tree-mortality rates vary over time, using data from the repeated censuses of our 66 plots. Two trends were apparent. First, although tree mortality was generally elevated near forest edges (Figure S1), it was also highly episodic, varying markedly among different census intervals. This is illustrated by the strong tendency for plots with high mean mortality rates (averaged over the entire study) to have significantly elevated CVs (Figure 4A). Second, mortality rates tended to decline somewhat with fragment age, at least among edge plots, which had the highest overall mortality rates (Figure 4B).

Figure 4. Temporal variability in tree mortality.

(A) Tree mortality is highly episodic in Amazonian forest fragments, as shown by the strong relationship between the mean and CV of mortality rates, based on repeated censuses of 1-ha plots (F1,64 = 13.17, R2 = 17.1%, P = 0.0006). (B) Mortality rates decline with fragment age, but only among plots near forest edges (F1,31 = 6.49, R2 = 17.3%, P = 0.016), which have the highest overall mortality rates (there was no significant trend for forest-interior plots; F1,31 = 0.42, R2 = 1.3%, P = 0.52; linear regressions).

https://doi.org/10.1371/journal.pone.0001017.g004

Collectively, these analyses suggest that elevated tree mortality partially drives changes in several other edge-effect phenomena, especially those relating to the intensity and pace of floristic change in fragments. Tree mortality is highly variable temporally and spatially, and tends to decline somewhat as fragments become older, especially among plots near forest edges. Although many edge phenomena were significantly affected by the proximity and number of nearby forest edges, as expected, they also differed to a surprisingly extent among the three large cattle ranches in our study area.

Discussion

Causes of variability in edge effects

For nearly three decades, we and our colleagues have studied ecological changes in forest fragments within a 1000-km2 experimental landscape, comprised by three large, isolated cattle ranches that were carved out of intact forest (Figure 1). Within these fragments, edge effects are clearly the dominant drivers of ecological change [5], [55], but the diverse edge phenomena we evaluated were often strikingly variable in space and time. Why?

Part of the pronounced spatial variability we observed arises from local factors such as the proximity and number of nearby forest edges (Tables 1, S1, and S2). Plots with two or more neighboring edges, such as those in small (1-ha) fragments and on the corners of larger fragments, have significantly greater tree mortality and biomass loss, fewer old-growth-tree seedlings [29], and higher abundances of pioneer and invasive tree species [30] and lianas [53], than do those with just one nearby edge. These patterns clearly support additive models of edge effects [28], which suggest that the intensity of edge phenomena is compounded by multiple nearby edges.

Edge age also influences edge effects. Edge-related tree mortality is especially intense in the first few years after edge creation (Figure 4)[5], [55], [62], in part because microclimatic changes are especially strong near newly formed edges, which are structurally open and thus highly permeable to the penetration of heat, light, and wind from outside degraded lands [24], [63]. In addition, most trees along newly formed edges are not physiologically acclimated to the sudden heat and desiccation stress, and many simply drop their leaves and die standing [5], [62]. Over time, the edge is partially sealed by proliferating vines and second growth, and microclimatic gradients lessen in intensity [7], [63]. Rates of tree death from physiological stress likely decline over time, both because older edges are less permeable and because trees that are poorly adapted for edge conditions (or in poor health generally) tend to die and be replaced by more desiccation-tolerant species [15]. These changes probably explain the moderate decline in tree-mortality rates with edge age observed in this study (Figure 4B).

Another driver of both spatial and temporal variability in edge effects is extreme weather events. The abrupt, artificial boundaries of forest fragments are especially vulnerable to windstorms, which can exert strong lateral-shear forces on exposed trees and create downwind turbulence for at least 2–10 times the height of the forest edge [64], [65]. In the Amazon, the most intense wind blasts come from convectional thunderstorms, which can cause severe but localized forest disturbance [66], [67]. Such windstorms are largely random events [66] that interact with local topography, leading to spatially complex patterns of forest disturbance [68]. Since our study commenced in 1979, fragments in the Dimona and, to a lesser extent, Porto Alegre ranches have been heavily damaged by windstorms, whereas those in Esteio ranch have remained largely unscathed [30], [38](Figure 1). These episodic wind disturbances cause considerable spatial and temporal variability in tree mortality and other correlated edge effects, such as floristic change and forest-biomass loss (Tables S1 and S2).

Periodic droughts also contribute to the temporal variability of edge effects, given the inherent vulnerability of rainforest edges to desiccation [23], [27]. Large areas of the Amazon are affected by the El Niño-Southern Oscillation (ENSO), which typically causes droughts or rainfall deficits at 3–7 year intervals. During the strong 1997 ENSO drought, dry-season rainfall was less than a third of average in our study area, and tree mortality and leaf-shedding by drought-stressed trees rose markedly near forest edges [40], [54]. In addition, destructive, edge-related forest fires proliferated dramatically across the Amazon [16], [42].

Finally, the structure and composition of the adjoining matrix vegetation can have a strong influence on edge effects. In our study area, forest edges adjoined by young regrowth forest, which helps to provide a physical buffer from wind and light, suffered less-intensive edge-related changes in microclimate [24] and lower tree mortality [32] than did those adjoined by cattle pastures. The species composition of the matrix vegetation is also important, because it influences the seed rain entering fragments [4], [27]. In our study area, tree species regenerating in fragments adjoined by Vismia-dominated regrowth were very different (more diverse and less dominated by the pioneer Cecropia sciadophylla) from those in fragments bordered by Cecropia-dominated regrowth [38]. Such differences can propel surprisingly rapid changes in the floristic composition of fragments [4], [15].

The ‘Landscape-Divergence Hypothesis’

In this study, several of the factors described above manifested themselves as important differences in edge effects among our three large cattle ranches (Table 1, Figure 3). Such differences initially surprised us. Our three sprawling ranches (Figure 1) were carved out of the surrounding old-growth forest almost simultaneously, as part of the same government-sponsored program to promote large-scale cattle ranching in the central Amazon. The three ranches had broadly similar vegetation and climate (despite certain differences in soils, slope, and their initial tree-community composition; see Methods and Protocol S1). Moreover, given that our study is a carefully controlled experiment, none of the ranches was subject to various complicating pressures, such as wildfires, selective logging, and overhunting, that plague many human-dominated landscapes [2], [69]. Yet despite such similarities, the fragments within the three landscapes have undertaken remarkably different trajectories of change. Why have these landscapes diverged?

The reason is that even small initial differences among the ranches quickly multiplied into much larger differences. Parts of the Porto Alegre and Esteio ranches were cleared in 1983, when an early wet season prevented burning of the felled forest [48]. Tall and floristically diverse Cecropia-dominated regrowth quickly developed in these areas, whereas areas cleared in other years became cattle pastures or, eventually, scrubby Vismia-dominated regrowth [70]. The differing matrix vegetation had major impacts on both the dynamics and trajectories of floristic change [15], [30], [38] and the composition of faunal communities [36], [48] in nearby fragments. These differences were magnified by subsequent windstorms, which severely damaged some fragments at Dimona and to a lesser extent at Porto Alegre, yet left the Esteio fragments unscathed. Even identically sized fragments in the three ranches have had remarkably different dynamics (Figure S1) and trajectories of compositional change.

The apparently acute sensitivity of fragments to local landscape and weather dynamics—even within a study area as initially homogeneous as ours—prompts us to propose a new hypothesis about the functioning of fragmented ecosystems. We suggest that fragments within the same landscape will tend to have similar dynamics and trajectories of change in species composition, which will often differ from those in other landscapes. Over time, we believe, this process will act as a homogenizing force for fragments within the same landscape, and will promote increasing ecological divergence among fragments in different landscapes (as a corollary, fragments that experience similar matrix, disturbance, and environmental conditions are predicted to converge in composition, even if they are not in the same vicinity). This concept is illustrated by the rapidly changing tree communities in our study area, which appear to be diverging in composition among the three cattle ranches (Figure 5), and by other key differences in ecological dynamics among the ranches (Table 1, Figure 3).

Figure 5. Increasing divergence of tree-community composition in three fragmented landscapes.

Tree communities in forest-edge plots (<100 m from the nearest edge) are shown before forest fragmentation and 13–18 years after fragmentation, based on a single ordination of all plots and censuses in the study area. The ordination used importance values for all 267 tree genera found in the plots.

https://doi.org/10.1371/journal.pone.0001017.g005

This ‘landscape-divergence hypothesis’ can be contrasted with the principle of nested subsets [71], [72], which predicts that habitat fragments across a region will converge in species composition—regardless of their disturbance history or local landscape features. According to the nested-subsets concept, the biota in low-diversity fragments will comprise a proper subset of those in higher-diversity fragments or intact habitat. Although the predictions of the landscape-divergence and nested-subsets hypotheses differ markedly, they are not mutually exclusive: habitat fragments in different landscapes could increasingly diverge over time, but still support subsets of the same high-diversity species pool found in intact habitat. Landscape divergence might help to explain, for example, the weakly nested structure observed in some fragmented communities [see 72 and references therein].

If our hypothesis is correct, then different fragmented landscapes may tend to diverge not only in species composition but also in ecosystem functioning. Differences in characteristics such as forest dynamics, carbon storage, functional-guild composition, and species invasions could gradually accumulate over time, leaving an increasingly pervasive signature of divergence on community composition and functioning. In practice, however, discriminating the effects of landscape divergence from preexisting patterns of beta diversity may not be straightforward, at least in the absence of pre-fragmentation data. Statistical techniques such as additive partitioning [73], [74] might be useful for apportioning variation in species diversity within and among landscapes, and thus for contrasting certain predictions of the nested-subsets versus landscape-divergence hypotheses.

Potential Implications

We conclude by highlighting three potential implications of our findings. First, the striking variability in edge effects we observed suggests that short-term or small-scale studies may fail to detect important edge phenomena, or may characterize them inadequately [7], [9]. In this study, our confidence was bolstered by the fact that we had pre-fragmentation data on tree-species distributions, stand structure, and biomass across our entire network of study plots. Even so, further replication would have been helpful for characterizing spatial variability in edge phenomena. Because of such inherent variability, it has been suggested that the known penetration-distance of edge effects should be doubled for management purposes [75], such as when designing buffer zones for nature reserves.

Second, our landscape-divergence hypothesis suggests that, rather than simply homogenizing biotas via selective extinctions, habitat fragmentation could also promote important landscape-scale differences among biotas. If so, this phenomenon should be incorporated into conservation planning, as it could imply, for example, that protected areas in different landscapes could preserve biologically and functionally different components of ecosystems.

Finally, our findings highlight the key impact of matrix vegetation on fragment dynamics [see also 76]. In the Amazon, among the worst (and unfortunately most common) land-use practices is one in which forest fragments are encircled by pastures, which are regularly burned by ranchers to control weeds and promote a flush of green grass for cattle. These fires destroy secondary vegetation and continually raze and re-open fragment edges, thereby maximizing the intensity of edge-related microclimatic stresses. Like a scab that is continually picked at, the forest edge cannot heal itself. During drought years, moreover, the rancher-lit fires can penetrate deep into fragments, greatly increasing forest degradation [41], [42]. In such contexts, protecting forest edges and their adjoining matrix is probably the single most important strategy for reducing the deleterious impacts of habitat fragmentation.

Materials and Methods

Study area and plots

The Biological Dynamics of Forest Fragments Project (BDFFP) is a 1000-km2 experimental landscape, dominated by non-flooded rainforest, located 80 km N of Manaus, Brazil (2°30′S, 60°W) at 50–100 m elevation (see Protocol S1 for details). The study area has three large (3,000–4,000 ha) cattle ranches, named Dimona, Porto Alegre, and Esteio, that contain a series of replicated forest fragments ranging from 1–100 ha in area. The fragments were created in the early-mid 1980s by felling and burning the surrounding forest to create cattle pastures. Nearby study sites in intact forest serve as experimental controls.

The three ranches in the study area are separated by expanses of primary forest and differ in certain respects [15], [30], [38], [48]. The ranches vary somewhat in slope, sand content, and soil-carbon content, and even before the fragments were created there were certain differences in tree abundance and species composition, but not tree-species richness, among the ranches (see Protocol S1). These initial disparities were greatly magnified by subsequent differences in land-use history among the ranches, which strongly influenced the amount and species composition of regrowth forest surrounding the fragments, and by wind disturbances, which had widely varying effects on the three ranches.

Prior to fragment isolation, standardized surveys of trees, mammals, birds, amphibians, many invertebrate groups, and other taxa were conducted in all fragment and control sites, and these and other taxa have since been monitored regularly. The ten edge-effect variables we evaluated were collected within a network of 66 1-ha permanent plots, arrayed across nine fragments and eight intact-forest sites. Plots were sampled at regular (typically 4–6 year) intervals, from the early-mid 1980s through 2004 (see Protocol S1). Nearly 1300 tree species or morphospecies have been identified in these plots.

Edge-effect variables

For each plot, data were collected on (1) annual rate of tree mortality, (2) annual rate of tree recruitment, (3) the CV in tree density across censuses, (4) annual rate of change in aboveground tree biomass, (5) liana abundance, (6) overall density of pioneer and invasive tree species (belonging to the genera Annona, Bellucia, Cecropia, Croton, Goupia, Jacaranda, Miconia, Pourouma, and Vismia), (7) mean rate of tree-species turnover, (8) overall rate of change in tree-community composition (using Euclidean distances to measure change in importance values for 267 tree genera), and (9 and 10) two vectors of floristic change in the plots (using an ordination analysis to assess trajectories of floristic change; see Protocol S1). These ten variables describe edge-related changes in forest dynamics and carbon storage (parameters 1–4), the abundance of key plant-functional groups (parameters 5–6), and plant species composition (parameters 7–10) in each plot.

Previous studies [11]–[13], [47]–[51] have revealed that all of these parameters are significantly altered near forest edges, but did not explicitly evaluate patterns of spatial and temporal variability in the parameters. All ten edge parameters were used to assess spatial (among-plot) variability in edge phenomena. Temporal (within-plot) variability was also evaluated for two of the most important edge phenomena, tree mortality and recruitment rates, because values could be generated for the individual plot censuses. In addition to these new analyses of edge-effect variability, this study includes five years of previously unpublished forest-dynamics data for our plots.

Predictor variables

We assessed the efficacy of seven key landscape, soil, and topographic factors to explain spatial variability in our edge-effect variables (see Protocol S1). These included (1) fragment/reserve area, (2) linear distance of each plot to the nearest forest edge, (3) the number of nearby forest edges, (4) cattle ranch (Dimona, Porto Alegre, Esteio), (5) soil percent sand content, (6) soil organic-carbon content, and (7) mean slope of each plot. Predictors 1, 3, and 4 were treated as categorical variables; all others were continuous.

Data analysis

General linear models (GLM) were employed to assess effects of predictor variables on edge-effect parameters, using Systat version 10. None of the predictors was strongly (R2>50%) intercorrelated. Log and arcsine-squareroot transformations were used as needed to improve data normality. GLM performance was assessed by comparing standardized residuals to the fitted values and to each significant predictor.

Acknowledgments

We thank Raphael Didham, Norman Kenkel, William Magnusson, and an anonymous referee for comments on the manuscript. This is publication number 493 in the BDFFP technical series.

Author Contributions

Conceived and designed the experiments: WL. Performed the experiments: WL SL. Analyzed the data: WL. Contributed reagents/materials/analysis tools: HN SL AA KH JR RL. Wrote the paper: WL. Other: Helped to conceptualize findings: RE.

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Term
Definition
predictable and orderly changes in the composition or structure of an ecological community.
Term
Definition
Succession that result from the formation of new soil (usually lava flow or retreat of glacier)
Term
Definition
Succession started by an even such as a fire or hurricane that reduced an established population to a smaller population of species
Term
Definition
the management of human activities so that ecosystems, their structure, function, composition and physical chemical and biological processes that shaped them continue to function.
Term
Explain how ecological and natural area management can be thought of as the manipulation of successional
processes, disturbances, or both.
Definition
Human influence on an area disrupts the natural process of succession (prevention of forest fires)
Term
Definition
describes a succession where the stimulus for change is an external one.

i.e. volcano, humans, grazing animal, flooding
Term
Definition
describes a succession where the stimulus for change is an internal one

i.e. soil improvement that allows a new species to develep
Term
How do the characteristics (plant functional type, biomass, density, plant morphology/longevity etc.)
change as succession progresses?
Definition
Term
Definition
In succession, a site begins with two pioneer species. As the forest the species that grows best w/o much shade will prosper. After this species is established the shade tolerant species will eventually take over as it receives more shade underneath the canopy of the other species and prospers.
Term
initial floristic composition?
Definition
suggests that species composition of vegetation following disturbance is determined by the propagules that exist on the site at the time of the disturbance and those which arrive early in the process of stand development. Changing species dominance over time results from differential growth and development of species present
Term
What is/are the main difference(s) between relay floristics and initial floristic composition?
Definition
The initial floristic composition will be a combination of the plants/seeds that were left after the disturbance events. Eventually plants more fit for the area will take over.
Term
Definition
weedy species, most energy goes to reproduction
Term
Definition
(Late succession species)tolerant, good competitors, tolerates shade, perennial
Term
What ingredients necessary for fire are present?
Definition
Wildfires occur when the necessary elements of a fire triangle intersect: an ignition source is brought into contact with a combustible material such as vegetation, that is subjected to sufficient heat and has an adequate supply of oxygen from the ambient air.
Term
Why does fire frequency (the number of fires over time in a given area) or fire return interval (time
between successive fires) vary with latitude and elevation? How do the characteristics of the vegetation
change associated with shifts in elevation/latitude?
Definition
Higher elevation/latitude = colder temps, less moisture, snow doesn't melt. Tree lines will grow up to the point where the environment can support tree life.

edge of treeline will also normally be warped from wind/lack of protection from elements
Term
What types of services are provided free of charge by ecosystems/species?
Definition
Clean drinking water, decomposition of waste, pharmaceuticals, energy
Term
What is colony collapse disorder and what species/organism is being impacted? Why is this a problem?
Definition
phenomenon in which worker bees in a hive suddenly disappear,(European honey bee) it is significant because bees pollinate many different crops
Term
How valuable are ecosystem services?
Definition
Very; clean water, decomposition of waste, pharmaceuticals
Term
How are ecologists beginning to convince people that ecosystem services are important?
Definition
Term
How does the Sixth Great Extinction differ from the previous five?
Definition
large spatial extent, impacting more organisms, human driven
Term
Why did some large organisms go extinct in North America around 10,000 years ago while others
survived?
Definition
human migration, rapid climate change (warming), hyperdisease (disease brought by humans that had a large effect on mammals 100 lbs +)
Term
Definition
Habit loss, Invasive species, populations (over population), pollution, over-consumption,climate change
Term
Linnaean Shortfall - what is it and what makes it problematic
Definition
Describes the difference between known species and species that exist. Most taxonomists live in cold climates; therefor only organisms in cold areas are discovered/observed
Term
Definition
extinctions of unknown species
Term
How many species are on earth that we know of (named) and how many species do we think exist?
Definition
1.7 million now named, 10-25 million estimated
Term
What is the background rate of extinctions and how does this differ from today?
Definition
10-100 species a years, now it is 30,000 species per year
Term
Pleistocene Overkill Hypothesis
Definition
about 14,000 years ago ancestors of native americans entered North America where the large predators had no previous interactions w/ humans and didn't see them as a threat which lead to over hunting to the point of extinction
Term
What is meant by the term minimum viable population and how is it defined?
Definition
minimum amount of organisms needed to exist w/o facing extinction from natural disasters, environmental, or genetic stochasticity (randomness)
Term
What are four sources of uncertainty that can influence small populations?
Definition
Term
Why are invasive species so much more common today than they have been in the past?
Definition
Human need to control environment - this wasn't a concern in the past (planting of gardens, introducing new species)
Term
How do we get invasive species (that is, what are main the reasons we have invasive species). You should
be able to provide an example species for each category.
Definition
Deliberate introductions - economic reasons, Asian carp and Nutria

Aesthetics - people moving and bringing familiar plants with them

biological control - cane toad, using one species to try and keep another species under control (usually doesn't work)

Accidental species introduction - boats moving from lake to lake w/o cleaning off the bottom of boat
Term
What are some possible ecosystem and species level traits that lead to successful invaders?
Definition
low amount of competitors/predators

short generation times/produce many offspring; helps w/ dispersal

broad niche

community vulnerability

underutilized niches
Term
Definition
Evolution of increased competitive ability - invasive species are not initially at an advantage, after a while they are able to take advantage of unused resources.

natural selection favors the reallocation of resources
Term
What are some explanations for how some organisms have become invasive? Examples?
Definition
Term
Why is it so hard to generalize concerning invasive species?
Definition
Unsure of the effects they will have in predation and competition....????
Term
If dispersal is a natural process, how are invasive species any different? What’s different today?
Definition
Human interaction w/ dispersal???
Term
Definition
1824; Given we have constant sunlight on the Earth, why isn’t it constantly heating up
Discovered that the atmosphere traps (and releases) energy
Term
Definition
1862; Discovers that particular gasses block radiation
Changes in concentration of ggases can change temperature
CO2
Term
Definition
1896;Published the first calculation of Earth’s temp if Co2 were doubled
-5 degrees C
Term
Definition
1938; Discovered first evidence of a temperature increase
Related to concentrations to CO2 in the the atmosphere
Term
How does the greenhouse effect work? What are the main gases that trap outgoing radiation?
Definition
CO2 and radiatively important trace (rits) trap out going infrared energy

CO2 and GHG’s are increasing
-200 parts per mil in 1900
-384 ppm today
-Methane: 25 more effecteive about 150%
-N2O (Nitrous oxide) 300 x Better at trapping energy
-Up 20%
Term
Why are CO2 and methane rising?
Definition
Humans - use of fossil fuels....more?
Term
What is the IPCC? Who comprises it and what do they do?
Definition
International Panel on Climate Change; evaluates the risk of climate change caused by human activity. Don't actually write anything, just summarize and approve based on vote
Term
What do climate models that use only natural forcing agents depict compared with models that incorporate
anthropogenic greenhouse gas emissions?
Definition
Term
Of all the things that influence temperatures, which have the largest impact (see slide from 12/03:
Attribution of Warming).
Definition
????? We didn't have class on 12/3, I can't find this slide
Term
What is the atmospheric concentration of CO2 today? How does this compare with the past and how do we
know what the concentrations were in the past?
Definition
384 parts/million today; 200 parts/million in 1900. How do we know?
Term
What characteristics of warming temperatures today appear to be different from warm periods of the past
(hint: think rate and area impacted).
Definition
Change is much more rapid and widespread
Term
How does climate change impact ecosystems?
Definition
force certain species out of their habitat while others flourish, may cause a mass extinction event as snow and water levels continue to change
Term
National Academy of Sciences
Definition
perform an unparalleled public service by bringing together experts in all areas of science. address critical national issues

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