■ Abstract The literature on effects of habitat fragmentation on biodiversity is huge. It is also very diverse, with different authors measuring fragmentation in different ways and, as a consequence, drawing different conclusions regarding both the magnitude and direction of its effects. Habitat fragmentation is usually defined as a landscape-scale process involving both habitat loss and the breaking apart of habitat. Results of empirical studies of habitat fragmentation are often difficult to interpret because (a) many researchers measure fragmentation at the patch scale, not the landscape scale and (b) most researchers measure fragmentation in ways that do not distinguish between habitat loss and habitat fragmentation per se, i.e., the breaking apart of habitat after controlling for habitat loss. Empirical studies to date suggest that habitat loss has large, consistently negative effects on biodiversity. Habitat fragmentation per se has much weaker effects on biodiversity that are at least as likely to be positive as negative. Therefore, to correctly interpret the influence of habitat fragmentation on biodiversity, the effects of these two components of fragmentation must be measured independently. More studies of the independent effects of habitat loss and fragmentation per se are needed to determine the factors that lead to positive versus negative effects of fragmentation per se. I suggest that the term “fragmentation” should be reserved for the breaking apart of habitat, independent of habitat loss.

/pdf/effects-of-habitat-fragmentation-on-biodiversity-4qxfu95ock.pdf

Effects of Habitat Fragmentation on Biodiversity

https://www.whoi.edu/cms/files/Ecological_Modelling_2002_Boyce_53558.pdf

Evaluating resource selection functions

▪ Abstract Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ...

https://www.kora.ch/malme/05_library/5_1_publications/C/Cote_et_al_2004_Ecological_impacts_of_deer_overabundance.pdf

Ecological Impacts of Deer Overabundance

Contrasting treatment‐specific survival using double‐robust estimators

How much habitat is enough

Recent declines in numbers and juvenile recruitment in many elk (Cervus elaphus) herds in the western U.S. has sparked interest in factors that may cause these declines. Inadequate nutrition or delayed parturition, the latter of which may be caused by inadequate numbers of mature bulls (i.e., highly skewed sex ratios), may have separate or synergistic effects on population dynamics and productivity. We evaluated the implications of late parturition and summer-autumn nutrition on reproduction and survival of Rocky Mountain elk (C. e. nelsoni) using a captive herd of 57 cow elk.



We induced early (Sep) and late breeding (Oct) and 3 levels of summer-autumn nutrition on the cows. Food was offered ad libitum at 3 levels of digestible energy (DE): high = 2.9-3.0 kcal of DE/g of diets, medium = 2.6-3.0 kcal/g, and low = 2.3-3.0 kcal/g. Within these ranges, DE content was gradually reduced from late June through early November to mimic seasonal changes in the wild. During summer and autumn, we measured calf growth; body mass, nutritional condition, and breeding dynamics of cows; and growth and pregnancy of yearlings. We also measured carry-over (i.e., time-lag) responses including over-winter calf and cow survival and parturition date and birth mass, as functions of previous summer-autumn nutrition and previous parturition date. Between autumn 1995 and spring 1998, we conducted 2 years of parturition-date, summer-autumn nutrition experiments, 2 winters of calf survival experiments, and 1 winter of cow survival experiments.



Early birth provided calves with more time to grow before onset of winter. This “head-start” advantage was maintained through late autumn, but its magnitude was diluted in some instances due to faster growth of some late-born calves. Body mass, body fat, and timing and probability of conception by cows in autumn were little influenced by parturition date the previous spring.



Summer-autumn nutrition significantly affected calves and their mothers. Growth of calves in the low and medium nutrition groups ceased by mid-September and late October. By December, calves in the high nutrition group were 40% and 70% heavier than calves in the medium and low groups, respectively. Cows in the high nutrition group accumulated about 75% and 300% more fat than cows in the medium and low groups by mid-October. Eighty percent of cows in the low nutrition group failed to conceive, and those in the medium group bred 10–14 days later than cows in the high group. Summer-autumn nutrition of calves influenced their probability of becoming pregnant as yearlings. Probability of pregnancy approached 100% for those yearlings that had high summerautumn nutrition as calves and yearlings, despite near starvation their first winter of life.



Winter survival of calves was related to their size at the onset of winter. Smaller calves lost more body mass daily than did large calves, and thus they survived fewer days through winter. Summer-autumn nutrition largely determined calf body size at the start of winter and, consequently, determined the proportion of winter survived. Survival of cows over winter was as related to body fat at the onset of winter as it was to nutrition during winter.



Carry-over effects of summer-autumn nutrition and parturition date on birth characteristics the following spring were minor. We detected no significant carry-over effect of summer-autumn nutrition or autumn condition on birth mass, although reduced condition in autumn delayed subsequent parturition date. Extent of body fat depletion in cows during the winter-survival experiments in 1998 accounted for 45% of the variation in parturition date. Ninety percent depletion delayed parturition an average of 34 days.



Delayed parturition, of a magnitude expected due to highly skewed sex ratios (3 weeks under extreme conditions), probably has only a weak influence on vital rates of free-ranging elk. In contrast, fat accretion and probability of pregnancy of cows, and growth and overwinter survival of calves, were sensitive to small (10–20%) differences in DE content of food. Digestible energy levels of our 2 lower nutrition levels reflect DE ranges reported for large ungulate herds during summer and autumn in western North America. Thus, our data suggest that limiting effects of summer-autumn nutrition on populations may be greater than often assumed, perhaps greater than those during winter in some ecosystems, and consequently indicate a need for greater understanding of nutrition's influence on population dynamics and how this influence varies across space and time. To enhance future research, we present animal- and vegetation-based guidelines for evaluating nutritional influences on elk populations.

/pdf/effects-of-summer-autumn-nutrition-and-parturition-date-on-fm1o396v4a.pdf

Effects of summer‐autumn nutrition and parturition date on reproduction and survival of elk

We analyzed demographic data from northern spotted owls (Strix occidentalis caurina) from 14 study areas in Washington, Oregon, and California for 1985–2003. The purpose of our analyses was to provide an assessment of the status and trends of northern spotted owl populations throughout most of their geographic range. The 14 study areas made up approximately 12% of the range of the subspecies and included federal, tribal, private, and mixed federal and private lands. The study areas also included all the major forest types that the subspecies inhabits. The analyses followed rigorous protocols that were developed a priori and were the result of extensive discussions and consensus among the authors. Our primary objectives were to estimate fecundity, apparent survival (φ), and annual rate of population change (λ) and to determine if there were any temporal trends in these population parameters. In addition to analyses of data from individual study areas, we conducted 2 meta-analyses on each demograph...

/pdf/status-and-trends-in-demography-of-northern-spotted-owls-uhbhfq9ohy.pdf

Status and trends in demography of northern spotted owls, 1985-2003

Spherical densiometers produce biased estimates of forest canopy cover

Des donnees demographiques montrent que de nombreuses populations de Wapitis des Rocheuses (Cervus elaphus nelsoni) et de Wapitis de Roosevelt (Cervus elaphus roosevelti) ont connu un declin au cours des dernieres decennies. De recents travaux semblent indiquer que la qualite du fourrage et son effet sur l’etat nutritionnel de l’animal, notamment a la fin de l’ete et au debut de l’automne, influencent la reproduction et la survie du wapiti. Nous avons estime l’etat nutritionnel saisonnier de 861 femelles dans 21 troupeaux au cours de 2 114 campagnes de capture realisees dans les etats de Washington, de l’Oregon, du Wyoming, du Colorado et du Dakota du Sud entre 1998 et 2007. Nous avons estime le taux de lipides sans ingesta et la masse corporelle et avons etabli l’âge, le taux de gestation et le taux de lactation. Pour la plupart des troupeaux, nous avons fait nos estimations a la fin de l’hiver/au debut du printemps (fin fev.-debut avr.) et a l’automne (nov.-debut dec.) afin de determiner si l’etat nutritionnel des individus variait au cours des saisons. Nos donnees semblent indiquer que les wapitis ont un regime alimentaire inadequat en ete et qu'il s'agit d'une situation generalisee. Les aires de repartition estivales de seulement 3 troupeaux sont parvenus a soutenir un taux de lipides et un taux de gestation relativement eleves en automne (taux de lipides de 11-13% et taux de gestation >90%), meme parmi les femelles qui avaient reussi, annee apres annee, a elever un petit. La plupart des autres aires de repartition soutenaient un taux de lipides peu eleve en automne (5% a 9%), et il etait courant de voir des pauses reproductives (taux de gestation <80%). Dans l'ensemble, nos donnees n'ont pas reussi a demontrer deux hypotheses repandues: 1) les conditions de fourrage en ete et au debut de l'automne sont generalement satisfaisantes pour prevenir les carences nutritionnelles chez les adultes en matiere d'accretion des lipides, de taux de gestation et de croissance des petits et des jeunes wapitis d'un an; et 2) l'alimentation et les conditions meteo hivernales sont les principaux facteurs limitatifs dans la reproduction du wapiti. Au contraire, nos donnees ont montre qu'il existait une tres forte correlation entre le regime alimentaire d'ete, le taux de lactation et la probabilite d'accouplement, correlation qui etait peu influencee par les conditions hivernales. C'etait plutot le caractere adequat du regime alimentaire d'ete qui regissait la performance reproductive des wapitis femelles et la croissance et le developpement de leur progeniture dans les montages des regions du nord-ouest et des Rocheuses. Nos travaux demontrent la necessite de mettre davantage l'accent sur les habitats d'ete dans les plans d'amenagement forestier en ce qui concerne les wapitis.

Larry L. Irwin

Papers

Effects of summer‐autumn nutrition and parturition date on reproduction and survival of elk

Status and trends in demography of northern spotted owls, 1985-2003

Spherical densiometers produce biased estimates of forest canopy cover

Regional and seasonal patterns of nutritional condition and reproduction in elk

Elk Habitat Use Relative to Forest Succession in Idaho