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Disturbance Hypothesis (disturbance + hypothesis)
Kinds of Disturbance Hypothesis Selected AbstractsEffects of repeated burning on species richness in a Florida pine savanna: A test of the intermediate disturbance hypothesisJOURNAL OF VEGETATION SCIENCE, Issue 1 2000Brian Beckage Wunderlin (1982) except for Aristida beyrichiana; which follows Peet (1993). Vouchers for each species were collected and deposited at the University of Central Florida herbarium Abstract. We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaike's Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model. [source] Testing the intermediate disturbance hypothesis: when will there be two peaks of diversity?DIVERSITY AND DISTRIBUTIONS, Issue 1 2005Karin Johst ABSTRACT Succession after disturbances generates a mosaic of patches in different successional stages. The intermediate disturbance hypothesis predicts that intermediate disturbances lead to the highest diversity of these stages on a regional scale resulting in a hump-shaped diversity,disturbance curve. We tested this prediction using field data of forest succession and hypothetical succession scenarios in combination with analytical and simulation models. According to our study the main factors shaping the diversity,disturbance curve and the position of the diversity maximum were the transition times between the successional stages, the transition type, neighbourhood effects and the choice of diversity measure. Although many scenarios confirmed the intermediate disturbance hypothesis we found that deviations in the form of two diversity maximums were possible. Such bimodal diversity,disturbance curves occurred when early and late successional stages were separated by one or more long-lived (compared to the early stages) intermediate successional stages. Although the field data which met these conditions among all those tested were rare (one of six), the consequences of detecting two peaks are fundamental. The impact of disturbances on biodiversity can be complex and deviate from a hump-shaped curve. [source] The concepts of ,plant functional types' and ,functional diversity' in lake phytoplankton , a new understanding of phytoplankton ecology?FRESHWATER BIOLOGY, Issue 9 2003Guntram Weithoff Summary 1. This is a discussion of the applicability to the phytoplankton of the concepts of ,plant functional types' (PFTs) and ,functional diversity' (FD), which originated in terrestrial plant ecology. 2. Functional traits driving the performance of phytoplankton species reflect important processes such as growth, sedimentation, grazing losses and nutrient acquisition. 3. This paper presents an objective, mathematical way of assigning PFTs and measuring FD. Ecologists can use this new approach to investigate general hypotheses [e.g. the intermediate disturbance hypothesis (IDH), the insurance hypothesis and synchronicity phenomena] as, for example, in its original formulation the IDH makes its predictions based on FD rather than species diversity. [source] Validation of plant functional types across two contrasting landscapesJOURNAL OF VEGETATION SCIENCE, Issue 2 2002Michael Kleyer Disturbance; Fertility; Logistic regression; Trait; Urban landscape Abstract. The validation of plant functional type models across contrasting landscapes is seen as a step towards the claim that plant functional types should recur regionally or even globally. I sampled the vegetation of an urban landscape on a range of sites representing gradients of resource supply and disturbance intensity. A group of plants with similar attributes was considered a ,functional type', if the species significantly co-occurred in a certain segment of the gradient plane of resource supply and disturbance intensity. Vegetative and regeneration traits were considered. A similar study was performed in a nearby agricultural landscape (Kleyer 1999). The logistic regression models from the urban landscape were applied to the data set of the agricultural landscape and vice versa. Although the overall environment of the two landscapes was very different, recurrent patterns of several functional types were found. At high fertility and high disturbance levels, annual species predominated with a persistent seed bank, high seed output, and short vertical expansion. When disturbances changed from below-ground to above-ground, the sexual regeneration mode was replaced by the vegetative mode, while vertical expansion remained low. At medium disturbance intensities, the vertical expansion and vegetative regeneration increased with fertility, while the seed bank remained mostly transient to short-term persistent and lateral expansion and sexual regeneration was intermediate. At low disturbances and low resource supplies, seed bank longevity, and vertical and lateral expansion tended to be long. Diversity of groups of plants with similar attributes was highest at intermediate disturbance levels and low fertility. These results correspond with Grime's humped-back model and Connell's intermediate disturbance hypothesis. [source] Effects of repeated burning on species richness in a Florida pine savanna: A test of the intermediate disturbance hypothesisJOURNAL OF VEGETATION SCIENCE, Issue 1 2000Brian Beckage Wunderlin (1982) except for Aristida beyrichiana; which follows Peet (1993). Vouchers for each species were collected and deposited at the University of Central Florida herbarium Abstract. We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaike's Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model. [source] How predictable are reptile responses to wildfire?OIKOS, Issue 7 2008David B. Lindenmayer Natural disturbances are key processes in the vast majority of ecosystems and a range of ecological theories have been developed in an attempt to predict biotic responses to them. However, empirical support for these theories has been inconsistent and considerable additional work remains to be done to better understand the response of biodiversity to natural disturbance. We tested predictions from the intermediate disturbance hypothesis and the habitat accommodation model of succession for reptile responses to fire history and a single major fire event. We focused our work on a broad range of vegetation types spanning sedgeland to temperate rainforest located within a national park in south-eastern Australia. We found no significant relationships between reptile species richness and the number of fires over the past 35 years, the time since the last fire, or the severity of a major fire in 2003. Thus, we found no strong evidence to support the intermediate disturbance hypothesis. A correspondence analysis of reptile assemblages revealed a gradient in species responses to fire history. However, we found limited evidence for an ordered succession of reptiles. Nor could the responses of individual species be readily predicted from life history attributes. Thus, our findings were generally not consistent with predictions from the habitat accommodation model of succession. A possible explanation for the absence of a predictable sequence of recovery following disturbance might be the rapidity of post-fire recovery of many components of native vegetation cover that were found to be important for reptiles (e.g. the extent of grass cover). This would have limited the time for early successional conditions to prevail and limited opportunities for species associated with such conditions. We found that most reptile species responses were much more strongly linked to vegetation type than fire variables, emphasizing a need to understand relationships with vegetation before being able to understand possible fire effects (if and where they exist). We found the disturbance concepts we examined were limited in their ability to accurately predict reptile responses to past fire history or the impacts of a single major fire in 2003. Practical management might be best guided not by disturbance theory, but by carefully setting objectives to meet conservation goals for particular individual species of reptiles. [source] Predicting invertebrate diversity from disturbance regimes in forest streamsOIKOS, Issue 1 2002Russell G. Death The link between substrate disturbance and stream invertebrate species richness is often complicated by the fact that substrate disturbance removes both invertebrates and periphyton (a potential food source). It is never clear whether disturbance acts directly on species diversity by removing animals or indirectly by reducing one of their food sources. To examine this relationship invertebrate diversity patterns were examined in 25 forest streams in Urewera National Park, New Zealand, where light attenuation from the forest canopy was postulated to limit periphyton biomass and remove the confounding influence of periphyton on the link between substrate disturbance and invertebrate diversity. Invertebrate species richness declined linearly with increasing substrate disturbance. Although periphyton biomass was comparatively low, species richness was more strongly related to periphyton biomass than to any disturbance measure. The highly mobile nature and terrestrial reproductive stage of many lotic invertebrates suggest that colonisation dynamics may have a more important influence on diversity patterns than monopolisation of resources for population growth. Although both the intermediate disturbance hypothesis and the dynamic equilibrium model encompass colonisation as a critical determinant of diversity both models also require a trade-off between the colonising and competitive ability of individual species; a phenomenon which does not appear to occur widely in lotic communities. Rather, it is postulated that resource levels will set an upper limit to the species richness of a benthic community that can be achieved through colonisation of taxa in the absence of disturbance, while disturbance removes taxa and resets the colonisation process. [source] Sequence effects of disturbance on community structureOIKOS, Issue 2 2001Tadashi Fukami The sequence in which disturbance events occur has the potential to affect the structure of ecological communities, but its role has been generally overlooked. Most disturbance studies have focused on the frequency or intensity of disturbance, probably reflecting the influence of the intermediate disturbance hypothesis. To investigate the effects of disturbance sequence on community structure, I created laboratory microcosms of protists and small metazoans analogous to communities found in water-filled bamboo stumps. Using drought (disturbance D) and larval mosquito addition (disturbance M), I examined the following five treatments of disturbance sequence: D-M-D-M, D-D-M-M, M-D-M-D, M-M-D-D, and no disturbance as a control. The response of species to disturbance varied between disturbance types (D or M) as well as among species, and disturbance effects depended on previous disturbance events. As a result, disturbance sequence drove the microcosms onto different successional trajectories, sometimes leading to divergence in final community states in terms of species richness or species composition and relative abundance. This divergence occurred even under the same frequency and intensity of disturbance. These results suggest that historical information on disturbance sequence can be essential for explaining variation in community structure. The interaction of sequence with frequency and intensity likely enhances the role played by disturbance in ecological communities. [source] | ||||||||||