1,721,159 research outputs found
The effects of domestic cat (Felis catus) density on urban bird abundance and richness
No full textCat predation is considered the greatest causes of bird mortality worldwide. I predict the effect of cats should be greatest on birds that are less than 150 grams on average, nest or feed on or low to the ground, feed at bird feeders, or are migrants. I tested these predictions using OBC bird surveys and cat density estimates across residential Ottawa. I compared bird abundance and species richness with cat density for all birds and those hypothesized to have a strong or weak effect of cats for each trait. I found cat density had little effect on bird abundance or species richness. Migrants were the only group that showed a significant effect of cats. My results suggest cats have little impact on urban bird abundance and richness, at least in urban regions where cat density is low and cats spend a large part of the year indoors
Forty years of bias in habitat fragmentation research
No full textThis chapter evaluates biases that contribute to the common misrepresentation of fragmentation as a major threat to biodiversity. The idea that habitat fragmentation seriously threatens biodiversity is so widespread that it might be considered a “conservation biology principle.” However, effects attributed to habitat fragmentation are usually confounded with effects of habitat loss. A recent review of the effects of habitat fragmentation per se (effects independent of habitat loss) indicated that 76% of significant effects of fragmentation were positive, and in no situation were most effects negative. Comparing the abstracts of papers with the actual results reported in the body of each paper revealed that fewer than half of the authors who found only positive fragmentation effects actually discuss these positive effects in their abstracts. Thus, authors themselves reinforce the misrepresentation of the fragmentation literature, potentially because authors fear that their results could be incorrectly used to justify habitat destruction.</p
Simulation Methods for Developing General Landscape-Level Hypotheses of Single-Species Dynamics
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Ecological Responses to Habitat Fragmentation Per Se
No full text For this article, I reviewed empirical studies finding significant ecological responses to habitat fragmentation per se—in other words, significant responses to fragmentation independent of the effects of habitat amount (hereafter referred to as habitat fragmentation). I asked these two questions: Are most significant responses to habitat fragmentation negative or positive? And do particular attributes of species or landscapes lead to a predominance of negative or positive significant responses? I found 118 studies reporting 381 significant responses to habitat fragmentation independent of habitat amount. Of these responses, 76% were positive. Most significant fragmentation effects were positive, irrespective of how the authors controlled for habitat amount, the measure of fragmentation, the taxonomic group, the type of response variable, or the degree of specialization or conservation status of the species or species group. No support was found for predictions that most significant responses to fragmentation should be negative in the tropics, for species with larger movement ranges, or when habitat amount is low; most significant fragmentation effects were positive in all of these cases. Thus, although 24% of significant responses to habitat fragmentation were negative, I found no conditions in which most responses were negative. Authors suggest a wide range of possible explanations for significant positive responses to habitat fragmentation: increased functional connectivity, habitat diversity, positive edge effects, stability of predator–prey/host–parasitoid systems, reduced competition, spreading of risk, and landscape complementation. A consistent preponderance of positive significant responses to fragmentation implies that there is no justification for assigning lower conservation value to a small patch than to an equivalent area within a large patch—instead, it implies just the opposite. This finding also suggests that land sharing will usually provide higher ecological value than land sparing. </jats:p
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