Plant networks are more connected by invasive brome and native shrub facilitation in Central California drylands

Dominant vegetation in many ecosystems is an integral component of structure and habitat. In many drylands, native shrubs function as foundation species that benefit other plants and animals. However, invasive exotic plant species can comprise a significant proportion of the vegetation. In Central California drylands, the facilitative shrub Ephedra californica and the invasive Bromus rubens are widely dispersed and common. Using comprehensive survey data structured by shrub and open gaps for the region, we compared network structure with and without this native shrub canopy and with and without the invasive brome. The presence of the invasive brome profoundly shifted the network measure of centrality in the microsites structured by a shrub canopy (centrality scores increased from 4.3 under shrubs without brome to 6.3, i.e. a relative increase of 42%). This strongly suggests that plant species such as brome can undermine the positive and stabilizing effects of native foundation plant species provided by shrubs in drylands by changing the frequency that the remaining species connect to one another. The net proportion of positive and negative associations was consistent across all microsites (approximately 50% with a total of 14% non-random co-occurrences on average) suggesting that these plant-plant networks are rewired but not more negative. Maintaining resilience in biodiversity thus needs to capitalize on protecting native shrubs whilst also controlling invasive grass species particularly when associated with shrubs.

The Overlooked Role of Facilitation in Biodiversity Experiments

Past research has demonstrated that decreased biodiversity often reduces ecosystem productivity, but variation in the shape of biodiversity-ecosystem function (BEF) relationships begets the need for a deeper mechanistic understanding of what drives these patterns. While mechanisms involving competition are often invoked, the role of facilitation is overlooked, or lumped within several less explicitly defined processes (e.g., complementarity effects). Here, we explore recent advances in understanding how facilitation affects BEF relationships and identify three categories of facilitative mechanisms that can drive variation in those relationships. Species interactions underlying BEF relationships are complex, but the framework we present provides a step toward understanding this complexity and predicting how facilitation contributes to the ecosystem role of biodiversity in a rapidly changing environment.

Positive interactions in communities

Current concepts of the role of interspecific interactions in communities have been shaped by a profusion of experimental studies of interspecific competition over the past few decades. Evidence for the importance of positive interactions - facilitations - in community organization and dynamics has accrued to the point where it warrants formal inclusion into community ecology theory, as it has been in evolutionary biology.

Autopsy in dementing illness: who participates?

The frequency of occurrence of various types of dementing disorders has been ascertained primarily from autopsied series. Since autopsy is voluntary, it is unknown if these series are representative of the entire demented population. To assess this issue, all deaths occurring over a 5-year period in our Memory Disorders Clinic were reviewed, and clinical variables and diagnoses were compared between patients who were autopsied and those who were not. Sixty-nine patients died; 43% (n = 30) underwent autopsy, and 57% (n = 39) did not. Race (no black patients were autopsied), age of disease onset, age of presentation to the clinic, age of death, and interval between last clinic contact and death (significantly less for nonautopsied patients) were found to differ between the two groups. However, clinical diagnosis of dementia was similar in the two groups. The clinical diagnosis was confirmed in 84% of autopsied patients. These results suggest that there are no major differences between clinical diagnoses for autopsied and non-autopsied patients and that the frequency of occurrence of various dementias obtained through autopsied series are representative of the demented population.

The relationship of high-intensity signals on magnetic resonance images to cognitive and psychiatric state in Alzheimer's disease

In Alzheimer's disease (AD), the relationship between white-matter changes on magnetic resonance images and behavior are unclear. Therefore, magnetic resonance images, cognition, and psychiatric state were assessed in patients with AD with depression (AD/DEP; n = 18) and without depression (AD; n = 45), older depressed patients (n = 12) and older normal individuals (n = 25). High-intensity signals in the cortex and subcortical regions were similar in number and proportions among all groups, even when hypertensive patients were excluded. No correlations to cognitive or psychiatric state were found. Periventricular signals were categorized using a 1- (absent) to 6- (thick, irregular caps and stripes) point scale. The categories were similar among groups except that patients with AD exhibited more category 5 changes than did normal subjects, neuropsychological performance was significantly worse in patients with AD who had category 5 and 6 changes when compared to those in category 1. These results suggest that periventricular changes may predict poor neuropsychological performance in patients with AD. However, neither deep white-matter lesions nor periventricular changes are useful for diagnostic purposes.

The clinical validity of the Mattis Dementia Rating Scale in staging Alzheimer's dementia

Considerable heterogeneity exists in the criteria used for the establishment of stages of impairment for patients with dementia. The valid distinction of stages is important both for clinical interpretation and the study of dementia. This study reports on the use of the Mattis Dementia Rating Scale (DRS) in staging dementia. Using a sample of 42 patients diagnosed with Alzheimer-type dementia, DRS performance and a rating of Instrumental Activities of Daily Living (IADL) were compared with clinical ratings of dementia severity. Total DRS score provides a clinically valid measure of stage of impairment and appeared to provide a better distinction among stages than IADL score. However, use of the IADL score in conjunction with total DRS may improve correspondence with clinical staging over use of the total DRS score alone. Normative data for the DRS are also provided.

The effect of long-term physostigmine administration in Alzheimer's disease

We assessed the effect of chronic long-term physostigmine in 20 patients with probable Alzheimer's disease. Initially, all patients went through a dose-finding phase and a double-blind crossover period, and were subsequently classified as physostigmine responders or nonresponders based on an a priori classification system. We then offered all patients long-term treatment with physostigmine regardless of their initial classification. Results revealed that responders spent significantly (p less than 0.0005) longer time periods on drug (36.1 +/- 4.6 months) than nonresponders (10.8 +/- 3.2). During a 2nd crossover period, 18 months into treatment, responders still demonstrated behavioral improvement, as assessed with the Sandoz Clinical Assessment-Geriatric Scale, whereas there were no behavioral changes observed in nonresponders. There were no effects on formal neuropsychological assessment. The results suggest that a subgroup of Alzheimer's patients benefits from long-term physostigmine therapy.

Biological and neuropsychological characterization of physostigmine responders and nonresponders in Alzheimer's disease

To assess the efficacy of oral physostigmine for the treatment of Alzheimer's disease, 20 patients were entered into a clinical trial. All patients underwent a dose-finding phase (two weeks), followed by an open trial (two weeks), and a double-blind crossover phase (two weeks drug, two weeks placebo). Extensive neuropsychological testing (Buschke Selective Reminding procedure, category generation, picture recognition, finger tapping) and measurement of systemic cholinergic parameters were measured during each of these phases. Patients were classified as physostigmine responders and nonresponders based on a priori established criteria. Using these, nine patients were found to respond to physostigmine, while 11 were classified as nonresponders. During baseline conditions, responders when compared to nonresponders were found to have higher concentrations of red blood cell (RBC) choline (Ch) and higher ratios of RBC Ch to plasma Ch. Neuropsychological tests were found to fall into one of three categories. The first group of tests were sensitive to drug effects and differentiated physostigmine responders from nonresponders; the second group was found to predict responsiveness; and the third group was neither predictive nor sensitive to drug effects.

Magnetic resonance imaging and the diagnosis of dementia

We describe seven patients with clinical, laboratory, and CT evidence of primary degenerative dementia (Alzheimer's, Pick's). Magnetic resonance imaging demonstrated regions in the white matter consistent with cerebral infarction. MRI may be a sensitive way to differentiate multi-infarct dementia and primary degenerative dementia.