Grantee Research Project Results

2002 Progress Report: Assessment of Extinction Risk in Dynamic Landscapes

EPA Grant Number: R829090
Title: Assessment of Extinction Risk in Dynamic Landscapes
Investigators: With, Kimberly A.
Institution: Kansas State University
EPA Project Officer: Hahn, Intaek
Project Period: October 29, 2001 through October 28, 2003
Project Period Covered by this Report: October 29, 2001 through October 28, 2002
Project Amount: $219,415
RFA: Wildlife Risk Assessment (2001) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems , Biology/Life Sciences

Objective:

The current global extinction crisis coincides with a period when landscapes are being transformed faster than ever before. Extinction risk thus needs to be assessed within a dynamic landscape context. Our primary goal is to develop insights into how multiple stressors of landscape change (the rate, magnitude, and degree of habitat fragmentation) affect the extinction risk for neotropical migratory songbirds, a species group of conservation concern. Our specific objectives are to: (1) assess the extinction risk for different species types in landscapes undergoing different rates of chronic habitat loss and fragmentation; (2) identify vulnerability thresholds for species in dynamic landscapes; (3) determine the relative effects of different aspects of the disturbance regime on extinction risk; (4) develop screening criteria to provide a general assessment of extinction risk for species in dynamic landscapes; and (5) identify scenarios where adaptive responses to landscape change might occur and mitigate extinction risk.

Progress Summary:

Preliminary Results. In the first phase of this research project, we addressed the problem of assessing the extinction risk for different types of migratory songbirds that varied in their sensitivity to habitat fragmentation by coupling a spatially structured avian demographic model with theoretical landscapes that were subjected to chronic habitat loss and fragmentation. The vulnerability threshold was defined as the point where the population growth rate () declined by 1 percent per annum habitat loss, analogous to the most conservative World Conservation Union criteria for assessing extinction risk. Counter to expectation, species appeared to persist across a greater range of habitat destruction when habitat loss was rapid (5 percent/year versus 0.5 percent/year). This paradox results from a lagged population response to landscape change. With a 5 percent habitat loss/year, the landscape is changing more rapidly than the demographic potential of the species. Demographically, the population already has crossed the vulnerability threshold, but consists of the “living dead;” individuals persist, but there is insufficient habitat remaining to produce offspring to support a viable population. It takes up to three times longer to reach this threshold in landscapes subjected to 0.5 percent/year habitat loss, which would potentially provide more time for developing and implementing conservation strategies for reversing population declines. A species’ sensitivity to edge effects (the rate at which reproductive success declines in habitat fragments owing to increased nest predation and brood parasitism in small fragments) had the greatest effect on extinction risk, but species with intermediate edge sensitivity exhibited the greatest sensitivity to habitat fragmentation (greatest shift in vulnerability threshold). We have made significant progress toward the completion of the first four objectives of this research project by: (1) assessing the effect of dynamic landscape change on extinction risk in Neotropical migrants; (2) identifying the vulnerability thresholds for various species in a dynamic landscape context; (3) determining the relative effects of different aspects of the landscape disturbance regime on extinction risk (the rate of disturbance had the greatest effect); and (4) developing simple screening criteria for assessing species' extinction risk (edge sensitivity is the most important predictor of extinction risk). With the appropriate demographic data (species' edge sensitivity and pertinent life-history parameters pertaining to clutch size, longevity, and survivorship) and information on the rate, magnitude, and duration of habitat destruction, this modeling approach could be implemented as an assessment tool to evaluate the extinction risk for real species in real landscapes.

We now are addressing the magnitude of habitat restoration required to reverse population declines and recover populations to a viable state, which represents an application related to the initial problem (i.e., determining the possibility of restoring landscapes to recover or stabilize populations identified at risk of extinction). We anticipate that restoration efforts may be ineffective below some critical level of landscape disturbance and rate of population decline (restoration thresholds). Habitat restoration is being simulated as a best-case scenario, in which the landscape is instantaneously renewed to 100 percent habitat before, at, or after the species' vulnerability threshold. The failure to stabilize or recover a population under this best-case scenario of habitat restoration would indicate that more modest levels and rates of restoration would not be sufficient for affecting a successful recovery. In preliminary results, habitat restoration was most effective for species with low to medium edge sensitivities and in landscapes that had not previously experienced extensive fragmentation. For species in heavily fragmented landscapes or in species that are highly edge sensitive, restoration needed to be initiated long before the vulnerability threshold (e.g., 20 years) to stabilize populations. Because of the erosion of demographic potential caused by habitat loss and fragmentation, populations cannot be recovered past this point through restoration alone (i.e., the restoration threshold), but likely would require additional conservation measures to increase survivorship, fecundity, or immigration rates among populations.

Significance of Findings. Assessments of extinction risk based on current landscape patterns may not be accurate without information on the history of landscape change. A species' risk of extinction on landscapes that appear structurally similar might be very different depending on the rate of disturbance and amount of time the landscape required to reach that state. Thus, traditional static landscape metrics based on the current amount and fragmentation of habitat may not be sufficient for evaluating extinction risk without invoking the "ghost of landscapes past." Identification of "vulnerability thresholds" ( 1 percent change in population growth rates per annum habitat loss) provides a more conservative measure of extinction risk than the extinction (persistence) threshold and thus would permit action to be taken sooner resulting in a proactive, rather than reactive, response to the conservation of declining populations.

Habitat restoration often is recommended as a means of conserving declining species. Rigorous assessments are seldom completed for habitat restoration to recover target populations. Our findings suggest that for species that are very sensitive to habitat fragmentation, habitat restoration would need to be initiated well before the population is assessed as being at risk of extinction (i.e., before the vulnerability threshold is crossed). Therefore, by the time a species is identified as being at risk of extinction (using a very conservative criterion), it already may be too little too late. In this case, such species are demographically limited rather than habitat limited, and thus habitat restoration cannot restore the population to a viable state. Other conservation measures would be needed to boost reproductive output or immigration rates and survivorship.

Future Activities:

During the remainder of this research project, we will address the following objectives: (1) how landscape connectivity affects the source-sink potential of landscape populations and thus extinction risk in a dynamic context (metalandscape analysis). There should be some critical level of connectivity (in terms of immigration rates) that is capable of mitigating extinction risk even in landscape undergoing chronic habitat destruction; and (2) the adaptive potential of populations in response to landscape change. Adaptive responses may be less important in well-connected landscapes and may not evolve in any case owing to dilution by immigrants from source populations where selective pressures are less severe.

We anticipate that Objective 1 will be completed during the summer of 2003 (June-August), and Objective 2 will be completed by January 2004. Thus, this research project should be completed within 2 months of the projected end date.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Publications Views

Other project views:	All 13 publications	7 publications in selected types	All 3 journal articles

Publications

Type	Citation	Project	Document Sources
Journal Article	Schrott GR, With KA, King ATW. On the importance of landscape history for assessing extinction risk. Ecological Applications.	R829090 (2002)	not available

Supplemental Keywords:

ecological effects, animal, population, terrestrial, ecology, modeling., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, wildlife, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, Habitat, Ecological Risk Assessment, Ecology and Ecosystems, ecological exposure, habitat dynamics, landscapes, extinction risk, dynamic landscapes, assessment models, adverse impacts, stressors, environmental stressor, extinction risk in dynamic landscapes, habitat disturbance, habitat loss, invasive species, assessment methods

Relevant Websites:

http://www.ksu.edu/withlab Exit

Progress and Final Reports:

Original Abstract

Final Report