Background and Aims Ontogenetic changes in anti-herbivore defences are common and result from variation in resource availability and herbivore damage throughout plant development. However, little is known about the simultaneous changes of multiple defences across the entire development of plants, and how such changes affect plant damage in the field. The aim of this study was to assess if changes in the major types of plant resistance and tolerance can explain natural herbivore damage throughout plant ontogeny. Methods An assessment was made of how six defensive traits, including physical, chemical and biotic resistance, simultaneously change across the major transitions of plant development, from seedlings to reproductive stages of Turnera velutina growing in the greenhouse. In addition, an experiment was performed to assess how plant tolerance to artificial damage to leaves changed throughout ontogeny. Finally, leaf damage by herbivores was evaluated in a natural population. Key Results The observed ontogenetic trajectories of all defences were significantly different, sometimes showing opposite directions of change. Whereas trichome density, leaf toughness, extrafloral nectary abundance and nectar production increased, hydrogen cyanide and compensatory responses decreased throughout plant development, from seedlings to reproductive plants. Only water content was higher at the intermediate juvenile ontogenetic stages. Surveys in a natural population over 3 years showed that herbivores consumed more tissue from juvenile plants than from younger seedlings or older reproductive plants. This is consistent with the fact that juvenile plants were the least defended stage. Conclusions The results suggest that defensive trajectories are a mixed result of predictions by the Optimal Defence Theory and the Growth-Differentiation Balance Hypothesis. The study emphasizes the importance of incorporating multiple defences and plant ontogeny into further studies for a more comprehensive understanding of plant defence evolution.

Resumen: La orientación de la ladera modifi ca las condiciones microclimáticas de los sitios. A pesar de este conocido patrón son pocas las evidencias de su efecto sobre las poblaciones de plantas y son aún más escasas para las cactáceas. En este estudio se determinó el efecto de la orientación de la ladera norte y sur sobre algunos atributos poblacionales (el área total del tallo, la densidad y la estructura de tamaños) y la ecomorfología (número y orientación de las ramas) de Neobuxbaumia tetetzo (Cactaceae) mayores a 1.5 m de alto en el Valle de Zapotitlán, Puebla. En la ladera sur se presentó una mayor densidad de tetechos y una mayor tendencia a orientar sus ramas hacia el noreste, que los tetechos de la ladera norte. Mientras que en la ladera norte los tetechos mostraron más ramifi caciones y hubo un menor número de tetechos de tamaño pequeño en comparación con la población de tetechos de la ladera sur. Se concluye que la orientación de la ladera afectó claramente la densidad, la estructura de tamaños y la ecomorfología de N. tetetzo; sin embargo, se requieren de estudios sobre los parámetros microclimáticos del sitio para poder hacer una generalización. Palabras clave: densidad, estructura de tamaños, orientación de las ramas, tetechos.Abstract: Slope orientation modifi es fi eld microclimatic conditions. Despite this well-known pattern, there is few empirical evidence of its infl uence on plant populations, and even lesser for cactus populations. Our goals were to determine the effect of N and S slope orientation on some population attributes (total stem area, density and size structure) and ecomorphology (number branch and orientation) of Neobuxbaumia tetetzo (Cactaceae) taller than 1.5 m in Valle de Zapotitlán, Puebla. In southerly slope, N. tetetzo showed higher density and a higher tendency of branches to northeast orientation than N. tetetzo in northerly slope. In the northern slope cacti had a higher number of branches than in the southern one. We conclude that slope orientation showed a remarkable effect on density, size structure, and ecomorphology of N. tetetzo; nevertheless, it is needed to obtain microclimatic records at the study site to clarify our understanding about slope orientation effect on N. tetezo population.