Truman P. Young

Restoration ecology and conservation biology

Restoration ecology is undergoing rapid growth as an academic discipline, similar to that experienced by conservation biology over the last 15 years. Restoration ecology and conservation biology share many underlying biodiversity goals, but diAer in striking ways. Using data from published literature in these two fields, I document that conservation biology has been more zoological, more descriptive and theoretical, and more focused on population and genetic studies than restoration ecology, which has been more botanical, more experimental, and more focused on population, community and ecosystem studies. I also use documented trends in population, land use, and biodiversity awareness to suggest that in the future ecological restoration will play an increasing role in biodiversity conservation. The conservation mind set is one of loss on a relatively short time horizon, whereas the restoration mind set is one of long-term recovery. I suggest that a restoration mind set can provide useful insights into problems of conservation today, illustrated with examples examining edge eAects and integrated conservation and development projects. # 1999 Elsevier Science Ltd. All rights reserved.

Principles for the Conservation of Wild Living Resources

We describe broadly applicable principles for the conservation of wild living resources and mechanisms for their implementation. These principles were engendered from three starting points. First, a set of principles for the conservation of wild living resources (Holt and Talbot 1978) required reexamination and updating. Second, those principles lacked mechanisms for implementation and consequently were not as effective as they might have been. Third, all conservation problems have scientific, economic, and social aspects, and although the mix may vary from problem to problem, all three aspects must be included in problem solving. We illustrate the derivation of, and amplify the meaning of, the principles, and discuss mechanisms for their implementation. The principles are: Principle I. Maintenance of healthy populations of wild living resources in perpetuity is inconsistent with unlimited growth of human consumption of and demand for those resources. Principle II. The goal of conservation should be to secure present and future options by maintaining biological diversity at genetic, species, population, and ecosystem levels; as a general rule neither the resource nor other components of the ecosystem should be perturbed beyond natural boundaries of variation. Principle III. Assessment of the possible ecological and sociological effects of resource use should precede both proposed use and proposed restriction or expansion of ongoing use of a resource. Principle IV. Regulation of the use of living resources must be based on understanding the structure and dynamics of the ecosystem of which the resource is a part and must take into account the ecological and sociological influences that directly and indirectly affect resource use. Principle V. The full range of knowledge and skills from the natural and social sciences must be brought to bear on conservation problems. Principle VI. Effective conservation requires understanding and taking account of the motives, interests, and values of all users and stakeholders, but not by simply averaging their positions. Principle VII. Effective conservation requires communication that is interactive, reciprocal, and continuous. Mechanisms for implementation of the principles are discussed.

Measuring association between individuals or groups in behavioural studies

Association indices have been used by ecologists, particularly in botanical studies, for many years . An understanding of how these indices were derived is critical to an understanding of why most of them are inappropriate for use in behavioural studies (see review in Cairns & Schwager 1987) . In ecological studies, indices are used to measure association of two species in space: how often (in how many transect sites) do two species co-occur? In answering this question, an attempt is made to reconcile two different, but real values . For instance, a particular species of tree may be found only in the woodlands while a species of grass may be found in both woodlands and plains . Let us assume that an even number of sites are censused in each habitat. In all woodland plots, grass and tree co-occur, so the association of grass and tree from the perspective of the tree species is 100% . In all grassland plots, the grass is found without the tree, so the association of the grass with the tree is 50% . This inequality can be expressed mathematically (definitions in Table I) . In an index of association for ecological purposes, y a and Yb are usually unequal. Therefore, the proportion of quadrats containing species A in which A and B co-occur [x/ (x +y,)] usually does not equal the percentage of quadrats containing species B in which A and B are found [x/(x+yb)] . Different association indices reconcile these two values in different ways (reviewed in Hubalek 1982). A single index of association can be derived from the two measures of association using the maximum value, the minimum value, the arithmetic mean, the geometric mean, and, perhaps most widely used, a weighted mean known as Sorensens index or Dices index (Pielou 1969) . The

Breakdown of an Ant-Plant Mutualism Follows the Loss of Large Herbivores from an African Savanna

Mutualisms are key components of biodiversity and ecosystem function, yet the forces maintaining them are poorly understood. We investigated the effects of removing large mammals on an ant-Acacia mutualism in an African savanna. Ten years of large-herbivore exclusion reduced the nectar and housing provided by plants to ants, increasing antagonistic behavior by a mutualistic ant associate and shifting competitive dominance within the plant-ant community from this nectar-dependent mutualist to an antagonistic species that does not depend on plant rewards. Trees occupied by this antagonist suffered increased attack by stem-boring beetles, grew more slowly, and experienced doubled mortality relative to trees occupied by the mutualistic ant. These results show that large mammals maintain cooperation within a widespread symbiosis and suggest complex cascading effects of megafaunal extinction.

Ants on swollen-thorn acacias: species coexistence in a simple system

Abstract On the black cotton soils of the Laikipia ecosystem in Kenya, two swollen-thorn acacia species support nine ant species, four of which are apparently obligate plant-ants. Among the ants, there are five species of Crematogaster, two species of Camponotus, and one each of Tetraponera and Lepisota. Acacia drepanolobium is host to four ant species that are both common and mutually exclusive. These four ant species, and an additional non-exclusive ant species, tend to occur on trees of different sizes, implying a succession of ant occupants. Nonetheless, all four exclusive species occur in substantial proportions on trees of intermediate size. There is direct evidence that an early successional ant species (Tetraponera penzigi) is actively evicted by two late successional ant species in the genus Crematogaster. There was also some evidence of height differentiation among ant species resident on A. seyal. Different acacia-ant species had different direct effects on A. drepanolobium. Extrafloral nectaries were eaten and destroyed only on trees inhabited by Tetraponera. Axillary shoots were eaten only on trees inhabited by C. nigriceps (potentially another early successional ant). This was associated with more new terminal shoots and healthier leaves than other trees, but also the virtual elimination of flowering and fruiting. Different resident acacia-ant species also had characteristic relationships with other insects. Among the four mutually exclusive ant species, only Crematogaster sjostedti was associated with two species of Camponotus, at least one of which (C. rufoglaucus) appears to be a foraging non-resident. A. drepanolobium trees occupied by C. sjostedti were also far more heavily infested with leaf galls than were trees occupied by other ant species. A. drepanolobium trees occupied by C. mimosae and C. sjostedti uniquely had tended adult scale insects. This diversity of ant inhabitants, and their strikingly different relationships with their hosts and other insect species, are examples of coexisting diversity on an apparently uniform resource.

Crown Asymmetry, Treefalls, and Repeat Disturbance of Broad-Leaved Forest Gaps

Gap—edge trees were significantly more likely to fall into pre—existing gaps than in other directions in a moist tropical forest on Barro Colorado Island (BCI), Panama. Trees not at gap edges were more likely to fall away from near neighbors than toward them. We show that gross asymmetries of tree crowns were the rule rather than the exception for all trees. The crowns of most gap—edge trees were strongly asymmetrical into their adjoining gaps, and trees not at gap edges were strongly asymmetrical way from near neighbors. Trees had a strong and significant tendency to fall on these heavy sides. Such treefalls, and related limbfalls, can result in redistribution of gaps and a retardation of gap regeneration. An analysis of 5 yr of canopy height data from a mapped 50—ha plot on BCI revealed that sites within larger gaps were significantly more likely to be redisturbed by secondary treefalls than were sites in the smallest gaps or nongap quadrats. These results suggest that treefall gaps in tropical forest may be more persistent disturbances than previously thought.

Thorns as induced defenses: experimental evidence

SummaryWe report evidence from controlled experiments that long straight thorns deter herbivory by browsers. Cut branches of three woody species that had their thorns removed suffered significantly greater herbivory by a tethered goat than did paired intact branches. Branches on living Acacia seyal plants that had their thorns removed suffered significantly greater herbivory by a wild population of free-ranging giraffes than did intact branches on the same plants. These differences in herbivory resulted in long term losses of branch length in clipped as opposed to control branches. In addition, branches within reach of giraffes produced longer thorns and a greater density of thorns than did higher branches. These results imply that increased thorn length is an induced defense.

Herbivore-initiated interaction cascades and their modulation by productivity in an African savanna

Despite conceptual recognition that indirect effects initiated by large herbivores are likely to have profound impacts on ecological community structure and function, the existing literature on indirect effects focuses largely on the role of predators. As a result, we know neither the frequency and extent of herbivore-initiated indirect effects nor the mechanisms that regulate their strength. We examined the effects of ungulates on taxa (plants, arthropods, and an insectivorous lizard) representing several trophic levels, using a series of large, long-term, ungulate-exclusion plots that span a landscape-scale productivity gradient in an African savanna. At each of six sites, lizards, trees, and the numerically dominant order of arthropods (Coleoptera) were more abundant in the absence of ungulates. The effect of ungulates on arthropods was mediated by herbaceous vegetation cover. The effect on lizards was simultaneously mediated by both tree density (lizard microhabitat) and arthropod abundance (lizard food). The magnitudes of the experimental effects on all response variables (trees, arthropods, and lizards) were negatively correlated with two distinct measures of primary productivity. These results demonstrate strong cascading effects of ungulates, both trophic and nontrophic, and support the hypothesis that productivity regulates the strength of these effects. Hence, the strongest indirect effects (and thus, the greatest risks to ecosystem integrity after large mammals are extirpated) are likely to occur in low-productivity habitats.

KLEE: A long‐term multi‐species herbivore exclusion experiment in Laikipia, Kenya

Abstract Livestock and wildlife share much of their respective ranges throughout the semi‐arid ecosystems of the world. As the profitability of livestock production becomes more marginal and wildlife values increase, there is a need to understand the interactions between livestock and wild large mammalian herbivores (and other indigenous biodiversity). To address this, we have established a long‐term multi‐species herbivore exclusion experiment in the Laikipia ecosystem in Kenya. Using a series of semi‐permeable barriers, we are differentially excluding various combinations of cattle, large wild mammalian herbivores, and mega‐herbivores (giraffes and elephants) from a series of replicated four‐hectare plots. We are monitoring soil, plant, and animal responses to these treatment characteristics. This multi‐disciplinary project is one of the first to include controlled, replicated exclusion of combinations of multiple guilds of rangeland herbivores in the same place at the same time. We report here (1) the ...

Alternative Outcomes of Natural and Experimental High Pollen Loads

Seed production is usually assumed to be a positive monotonic function of pollen deposition and/or pollinator visitation. If this assumption were correct, there would be only two outcomes of excess pollen levels: an increase in fruit or seed set, or no increase. However, a substantial minority of the studies reviewed here has found that seed production declines with increased pollen loads, both under experimental and natural conditions. To explain this decrease, we propose the following mechanisms: pollen tube crowding, pollen removal or stigma damage by pollen thieves or pollinators, stigma damage during hand- pollination, application of low-diversity or local pollen, effects of bagging flowers, missed stigma receptivity, and the application of inviable pollen. These mechanisms can be dis- tinguished through more complete and more careful experimental designs and incremental pollen supplementation.